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<h1>Apache Kudu Prior Version Release Notes</h1>
<div id="preamble">
<div class="sectionbody">
<div class="paragraph">
<p>This section reproduces the release notes for new features and incompatible
changes in prior releases of Apache Kudu.</p>
</div>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
The list of known issues and limitations for prior releases are not
reproduced on this page. Please consult the
<a href="http://kudu.apache.org/releases/">documentation of the appropriate release</a>
for a list of known issues and limitations.
</td>
</tr>
</table>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.5.0"><a class="link" href="#rn_1.5.0">Release notes specific to 1.5.0</a></h2>
<div class="sectionbody">
</div>
</div>
<div class="sect1">
<h2 id="rn_1.5.0_upgrade_notes"><a class="link" href="#rn_1.5.0_upgrade_notes">Upgrade Notes</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Kudu 1.5 now enables the optional ability to compute, store, and verify
checksums on all pieces of data stored on a server by default. Due to
storage format changes, downgrading to versions 1.3 or earlier is not
supported and will result in an error.</p>
</li>
<li>
<p>Spark 2.2+ requires Java 8 at runtime even though Kudu Spark 2.x integration
is Java 7 compatible. Spark 2.2 is the default dependency version as of
Kudu 1.5.0.</p>
</li>
<li>
<p>The kudu-spark-tools module has been renamed to kudu-spark2-tools_2.11 in
order to include the Spark and Scala base versions. This matches the pattern
used in the kudu-spark module and artifacts.</p>
</li>
<li>
<p>To improve security, world-readable Kerberos keytab files are no longer
accepted by default. Set <code>--allow_world_readable_credentials=true</code> to override
this behavior. See
<a href="https://issues.apache.org/jira/browse/KUDU-1955">KUDU-1955</a> for additional
details.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.5.0_deprecations"><a class="link" href="#rn_1.5.0_deprecations">Deprecations</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Support for Java 7 is deprecated as of Kudu 1.5.0 and may be removed in the
next major release.</p>
</li>
<li>
<p>Support for Spark 1 (kudu-spark_2.10) is deprecated as of Kudu 1.5.0 and may
be removed in the next minor release.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.5.0_new_features"><a class="link" href="#rn_1.5.0_new_features">New features</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Tablet servers are now optionally able to tolerate disk failures at
startup. This feature is experimental; by default, Kudu will crash if it
experiences a disk failure. When enabled, tablets with any data on the failed
disk will not be opened and will be replicated as needed. To enable this, set
the <code>--crash_on_eio</code> flag to <code>false</code>. Additionally, there is a configurable
tradeoff between a newly added tablet&#8217;s tolerance to disk failures and its
parallelization of I/O via the <code>--fs_target_data_dirs_per_tablet</code> flag.
Tablets that are spread across fewer disks are less likely to be affected by a
disk failure, at the cost of reduced parallelism. Note that the first
configured data directory and the WAL directory cannot currently tolerate disk
failures, and disk failures during run-time are still fatal.</p>
</li>
<li>
<p>Kudu server web UIs have a new configuration dashboard (/config) which
provides a high level summary of important security configuration values, such
as whether RPC authentication is required, or web server HTTPS encryption is
enabled. Other types of configuration will be added in future releases.</p>
</li>
<li>
<p>The <code>kudu</code> command line tool has two new features: <code>kudu tablet move</code> and
<code>kudu local_replica data_size</code>. The 'tablet move' tool moves a tablet replica
from one tablet server to another, under the condition that the tablet is
healthy. An operator can use this tool to rebalance tablet replicas between
tablet servers. The 'local replica data size' tool summarizes the space usage
of a tablet, breaking it down by type of file, column, and rowset.</p>
</li>
<li>
<p>kudu-client-tools now supports exporting CSV files and importing
Apache Parquet files. This feature is unstable and may change APIs and
functionality in future releases.</p>
</li>
<li>
<p>kudu-spark-tools now supports importing and exporting CSV, Apache Avro and
Apache Parquet files. This feature is unstable and may change APIs and
functionality in future releases.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.5.0_optimizations_improvements"><a class="link" href="#rn_1.5.0_optimizations_improvements">Optimizations and improvements</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>The log block manager now performs disk synchronization in batches.
This optimization can significantly reduce the time taken to copy tablet data
from one server to another; in one case tablet copy time is reduced by 35%.
It also improves the general performance of flushes and compactions.</p>
</li>
<li>
<p>A new feature referred to as "tombstoned voting" is added to the Raft
consensus subsystem to allow tablet replicas in the <code>TABLET_DATA_TOMBSTONED</code>
state to vote in tablet leader elections. This feature increases Kudu&#8217;s
stability and availability by improving the likelihood that Kudu will be able
to self-heal in more edge-case scenarios, such as when tablet copy operations
fail. See <a href="https://issues.apache.org/jira/browse/KUDU-871">KUDU-871</a> for
details.</p>
</li>
<li>
<p>The tablet on-disk size metric has been made more accurate. Previously, the
metric included only REDO deltas; it now counts all deltas. Additionally, the
metric includes the size of bloomfiles, ad hoc indexes, and the tablet
superblock. WAL segments and consensus metadata are still not counted. The
latter is very small compared to the size of data, but the former may be
significant depending on the workload (this will be resolved in a future
release).</p>
</li>
<li>
<p>The number of threads used by the Kudu tablet server has been further reduced.
Previously, each follower tablet replica used a dedicated thread to detect
leader tablet replica failures, and each leader replica used one dedicated
thread per follower to send Raft heartbeats to that follower. The work
performed by these dedicated threads has been reassigned to other threads.
Other improvements were made to facilitate better thread sharing by tablets.
For the purpose of capacity planning, expect the Kudu tablet server to create
one thread for every five "cold" (i.e. those not servicing writes) tablets,
and an additional three threads for every "hot" tablet. This will be further
improved upon in future Kudu releases.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.5.0_fixed_issues"><a class="link" href="#rn_1.5.0_fixed_issues">Fixed Issues</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>The Java Kudu client now automatically requests new authentication tokens
after expiration. As a result, long-lived Java clients are now supported. See
<a href="https://issues.apache.org/jira/browse/KUDU-2013">KUDU-2013</a> for more
details.</p>
</li>
<li>
<p>Multiple Kerberos compatibility bugs have been fixed, including support
for environments with disabled reverse DNS, FreeIPA compatibility, principal
names including uppercase characters, and hosts without a FQDN.</p>
</li>
<li>
<p>A bug in the binary prefix decoder which could cause a tablet server 'check'
assertion crash has been fixed. The crash could only be triggered in very
specific scenarios; see
<a href="https://issues.apache.org/jira/browse/KUDU-2085">KUDU-2085</a> for additional
details.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.5.0_wire_compatibility"><a class="link" href="#rn_1.5.0_wire_compatibility">Wire Protocol compatibility</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 1.5.0 is wire-compatible with previous versions of Kudu:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Kudu 1.5 clients may connect to servers running Kudu 1.0 or later. If the client uses
features that are not available on the target server, an error will be returned.</p>
</li>
<li>
<p>Rolling upgrade between Kudu 1.4 and Kudu 1.5 servers is believed to be possible
though has not been sufficiently tested. Users are encouraged to shut down all nodes
in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
</li>
<li>
<p>Kudu 1.0 clients may connect to servers running Kudu 1.5 with the exception of the
below-mentioned restrictions regarding secure clusters.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The authentication features introduced in Kudu 1.3 place the following limitations
on wire compatibility between Kudu 1.5 and versions earlier than 1.3:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>If a Kudu 1.5 cluster is configured with authentication or encryption set to "required",
clients older than Kudu 1.3 will be unable to connect.</p>
</li>
<li>
<p>If a Kudu 1.5 cluster is configured with authentication and encryption set to "optional"
or "disabled", older clients will still be able to connect.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.5.0_incompatible_changes"><a class="link" href="#rn_1.5.0_incompatible_changes">Incompatible Changes in Kudu 1.5.0</a></h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="rn_1.5.0_client_compatibility"><a class="link" href="#rn_1.5.0_client_compatibility">Client Library Compatibility</a></h3>
<div class="ulist">
<ul>
<li>
<p>The Kudu 1.5 Java client library is API- and ABI-compatible with Kudu 1.4. Applications
written against Kudu 1.4 will compile and run against the Kudu 1.5 client library and
vice-versa, unless one of the following newly added APIs is used:</p>
</li>
<li>
<p>The Kudu 1.5 C++ client is API- and ABI-forward-compatible with Kudu 1.4.
Applications written and compiled against the Kudu 1.4 client library will run without
modification against the Kudu 1.5 client library. Applications written and compiled
against the Kudu 1.5 client library will run without modification against the Kudu 1.4
client library.</p>
</li>
<li>
<p>The Kudu 1.5 Python client is API-compatible with Kudu 1.4. Applications
written against Kudu 1.4 will continue to run against the Kudu 1.5 client
and vice-versa.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.4.0"><a class="link" href="#rn_1.4.0">Release notes specific to 1.4.0</a></h2>
<div class="sectionbody">
</div>
</div>
<div class="sect1">
<h2 id="rn_1.4.0_upgrade_notes"><a class="link" href="#rn_1.4.0_upgrade_notes">Upgrade Notes</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>The Maintenance Manager now fully uses the threads it&#8217;s given (see the improvements
described further below), so it&#8217;s now able to generate a lot more IO by flushing and
compacting more often. Generally, the recommended ratio of MM threads to data
directories is 1:3; operators of clusters above that ratio should be mindful of
this when upgrading.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.4.0_new_features"><a class="link" href="#rn_1.4.0_new_features">New features</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>The C++ and Java client libraries now support the ability to alter the
storage attributes (e.g. encoding and compression) and default value
of existing columns. Additionally, it is now possible to rename
a column which is part of a table&#8217;s primary key.</p>
</li>
<li>
<p>The C++ client library now includes an experimental <code>KuduPartitioner</code> API which may
be used to efficiently map rows to their associated partitions and hosts.
This may be used to achieve better locality or distribution of writes
in client applications.</p>
</li>
<li>
<p>The Java client library now supports enabling fault tolerance on scanners.
Fault tolerant scanners are able to transparently recover from concurrent
server crashes at the cost of some performance overhead. See the Java
API documentation for more details on usage.</p>
</li>
<li>
<p>The <code>kudu</code> command line tool now includes a new advanced administrative
command <code>kudu remote_replica unsafe_change_config</code>. This command may be used
to force a tablet to perform an unsafe change of its Raft replication
configuration. This can be used to recover from scenarios such as a loss
of a majority of replicas, at the risk of losing edits.</p>
</li>
<li>
<p>The <code>kudu</code> command line tool now includes the <code>kudu fs check</code> command
which performs various offline consistency checks on the local on-disk
storage of a Kudu Tablet Server or Master. In addition to detecting
various inconsistencies or corruptions, it can also detect and remove
data blocks that are no longer referenced by any tablet but were not
fully removed from disk due to a crash or a bug in prior versions of Kudu.</p>
</li>
<li>
<p>The <code>kudu</code> command line tool can now be used to list the addresses and
identifiers of the servers in the cluster using either <code>kudu master list</code>
or <code>kudu tserver list</code>.</p>
</li>
<li>
<p>Kudu 1.4 now includes the optional ability to compute, store, and verify
checksums on all pieces of data stored on a server. Prior versions only
performed checksums on certain portions of the stored data. This feature
is not enabled by default since it makes a backward-incompatible change
to the on-disk formats and thus prevent downgrades. Kudu 1.5 will enable
the feature by default.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_optimizations_and_improvements"><a class="link" href="#_optimizations_and_improvements">Optimizations and improvements</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p><code>kudu cluster ksck</code> now detects and reports new classes of
inconsistencies and issues. In particular, it is better able to
detect cases where a configuration change such as a replica eviction
or addition is pending but is unable to be committed. It also now
properly detects and reports cases where a tablet has no elected
leader.</p>
</li>
<li>
<p>The default size for Write Ahead Log (WAL) segments has been reduced
from 64MB to 8MB. Additionally, in the case that all replicas of a
tablet are fully up to date and data has been flushed from memory,
servers will now retain only a single WAL segment rather than
two. These changes are expected to reduce the average consumption of
disk space on the configured WAL disk by 16x, as well as improve the
startup speed of tablet servers by reducing the number and size of
WAL segments that need to be re-read.</p>
</li>
<li>
<p>The default on-disk storage system used by Kudu servers (Log Block Manager)
has been improved to compact its metadata and remove dead containers.
This compaction and garbage collection occurs only at startup. Thus, the
first startup after upgrade is expected to be longer than usual, and
subsequent restarts should be shorter.</p>
</li>
<li>
<p>The usability of the Kudu web interfaces has been improved,
particularly for the case where a server hosts many tablets or a
table has many partitions. Pages that list tablets now include
a top-level summary of tablet status and show the complete list
under a toggleable section.</p>
</li>
<li>
<p>The Maintenance Manager has been improved to improve utilization of the
configured maintenance threads. Previously, maintenance work would
only be scheduled a maximum of 4 times per second, but now maintenance
work will be scheduled immediately whenever any configured thread is
available. This can improve the throughput of write-heavy workloads.</p>
</li>
<li>
<p>The Maintenance Manager will now aggressively schedule flushes of
in-memory data when memory consumption crosses 60% of the configured
process-wide memory limit. The backpressure mechanism which begins
to throttle client writes has been accordingly adjusted to not begin
throttling until reaching 80% of the configured limit. These two
changes together result in improved write throughput, more consistent
latency, and fewer timeouts due to memory exhaustion.</p>
</li>
<li>
<p>Many performance improvements were made to write performance. Applications
which send large batches of writes to Kudu should see substantially
improved throughput in Kudu 1.4.</p>
</li>
<li>
<p>Several improvements were made to reduce the memory consumption of
Kudu Tablet Servers which hold large volumes of data. The specific
amount of memory saved varies depending on workload, but the expectation
is that approximately 350MB of excess peak memory usage has been eliminated
per TB of data stored.</p>
</li>
<li>
<p>The number of threads used by the Kudu Tablet Server has been reduced.
Previously, each tablet used a dedicated thread to append to its WAL.
Those threads now automatically stop running if there is no activity
on a given tablet for a short period of time.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.4.0_fixed_issues"><a class="link" href="#rn_1.4.0_fixed_issues">Fixed Issues</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-2020">KUDU-2020</a>
Fixed an issue where re-replication after a failure would proceed
significantly slower than expected. This bug caused many tablets
to be unnecessarily copied multiple times before successfully
being considered re-replicated, resulting in significantly more
network and IO bandwidth usage than expected. Mean time to recovery
on clusters with large amounts of data is improved by up to 10x by this
fix.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1982">KUDU-1982</a>
Fixed an issue where the Java client would call <code>NetworkInterface.getByInetAddress</code>
very often, causing performance problems particularly on Windows
where this function can be quite slow.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1755">KUDU-1755</a>
Improved the accuracy of the <code>on_disk_size</code> replica metrics to
include the size consumed by bloom filters, primary key indexes,
and superblock metadata, and delta files. Note that, because the size
metric is now more accurate, the reported values are expected to
increase after upgrading to Kudu 1.4. This does not indicate that
replicas are using more space after the upgrade; rather, it is
now accurately reporting the amount of space that has always been
used.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1192">KUDU-1192</a>
Kudu servers will now periodically flush their log messages to disk
even if no <code>WARNING</code>-level messages have been logged. This makes it
easier to tail the logs to see progress output during normal startup.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1999">KUDU-1999</a>
Fixed the ability to run Spark jobs in "cluster" mode against
Kudu clusters secured by Kerberos.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.4.0_wire_compatibility"><a class="link" href="#rn_1.4.0_wire_compatibility">Wire Protocol compatibility</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 1.4.0 is wire-compatible with previous versions of Kudu:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Kudu 1.4 clients may connect to servers running Kudu 1.0 or later. If the client uses
features that are not available on the target server, an error will be returned.</p>
</li>
<li>
<p>Kudu 1.0 clients may connect to servers running Kudu 1.4 with the exception of the
below-mentioned restrictions regarding secure clusters.</p>
</li>
<li>
<p>Rolling upgrade between Kudu 1.3 and Kudu 1.4 servers is believed to be possible
though has not been sufficiently tested. Users are encouraged to shut down all nodes
in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The authentication features introduced in Kudu 1.3 place the following limitations
on wire compatibility between Kudu 1.4 and versions earlier than 1.3:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>If a Kudu 1.4 cluster is configured with authentication or encryption set to "required",
clients older than Kudu 1.3 will be unable to connect.</p>
</li>
<li>
<p>If a Kudu 1.4 cluster is configured with authentication and encryption set to "optional"
or "disabled", older clients will still be able to connect.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.4.0_incompatible_changes"><a class="link" href="#rn_1.4.0_incompatible_changes">Incompatible Changes in Kudu 1.4.0</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Kudu servers, by default, will now only allow unencrypted or unauthenticated connections
from trusted subnets, which are private networks (127.0.0.0/8,10.0.0.0/8,172.16.0.0/12,
192.168.0.0/16,169.254.0.0/16) and local subnets of all local network interfaces.
Unencrypted or unauthenticated connections from publicly routable IPs will be rejected,
even if encryption and authentication are not configured.</p>
<div class="paragraph">
<p>The trusted subnets can be configured using the <code>--trusted_subnets</code> flag, which can be set
to IP blocks represented in CIDR notation separated by comma. Set it to '0.0.0.0/0' to
allow unauthenticated connections from all remote IP addresses. However, if network access
is not otherwise restricted by a firewall, malicious users may be able to gain unauthorized
access. This can be mitigated if authentication and encryption are configured to be
required.</p>
</div>
</li>
</ul>
</div>
<div class="sect2">
<h3 id="rn_1.4.0_client_compatibility"><a class="link" href="#rn_1.4.0_client_compatibility">Client Library Compatibility</a></h3>
<div class="ulist">
<ul>
<li>
<p>The Kudu 1.4 Java client library is API- and ABI-compatible with Kudu 1.3. Applications
written against Kudu 1.3 will compile and run against the Kudu 1.4 client library and
vice-versa, unless one of the following newly added APIs is used:</p>
<div class="ulist">
<ul>
<li>
<p><code>[Async]KuduScannerBuilder.setFaultTolerant(&#8230;&#8203;)</code></p>
</li>
<li>
<p>New methods in <code>AlterTableOptions</code>: <code>removeDefault</code>, <code>changeDefault</code>, <code>changeDesiredBlockSize</code>,
<code>changeEncoding</code>, <code>changeCompressionAlgorithm</code></p>
</li>
<li>
<p><code>KuduClient.updateLastPropagatedTimestamp</code></p>
</li>
<li>
<p><code>KuduClient.getLastPropagatedTimestamp</code></p>
</li>
<li>
<p>New getters in <code>PartialRow</code>: <code>getBoolean</code>, <code>getByte</code>, <code>getShort</code>, <code>getInt</code>, <code>getLong</code>,
<code>getFloat</code>, <code>getDouble</code>, <code>getString</code>, <code>getBinaryCopy</code>, <code>getBinary</code>, <code>isNull</code>,
<code>isSet</code>.</p>
</li>
</ul>
</div>
</li>
<li>
<p>The Kudu 1.4 C++ client is API- and ABI-forward-compatible with Kudu 1.3.
Applications written and compiled against the Kudu 1.3 client library will run without
modification against the Kudu 1.4 client library. Applications written and compiled
against the Kudu 1.4 client library will run without modification against the Kudu 1.3
client library unless they use one of the following new APIs:</p>
<div class="ulist">
<ul>
<li>
<p><code>KuduPartitionerBuilder</code></p>
</li>
<li>
<p>`KuduPartitioner</p>
</li>
<li>
<p><code>KuduScanner::SetRowFormatFlags</code> (unstable API)</p>
</li>
<li>
<p><code>KuduScanBatch::direct_data</code>, <code>KuduScanBatch::indirect_data</code> (unstable API)</p>
</li>
</ul>
</div>
</li>
<li>
<p>The Kudu 1.4 Python client is API-compatible with Kudu 1.3. Applications
written against Kudu 1.3 will continue to run against the Kudu 1.4 client
and vice-versa.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.3.0"><a class="link" href="#rn_1.3.0">Release notes specific to 1.3.0</a></h2>
<div class="sectionbody">
</div>
</div>
<div class="sect1">
<h2 id="rn_1.3.0_new_features"><a class="link" href="#rn_1.3.0_new_features">New features</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Kudu 1.3 adds support for strong authentication based on Kerberos. This optional feature
allows users to authenticate themselves using Kerberos tickets, and also provides
mutual authentication of servers using Kerberos credentials stored in keytabs. This
feature is optional, but recommended for deployments requiring security.</p>
</li>
<li>
<p>Kudu 1.3 adds support for encryption of data on the network using Transport Layer Security
(TLS). Kudu will now use TLS to encrypt all network traffic between clients and servers as
well as any internal traffic among servers, with the exception of traffic determined to
be within a localhost network connection. Encryption is enabled by default whenever it can
be determined that both the client and server support the feature.</p>
</li>
<li>
<p>Kudu 1.3 adds coarse-grained service-level authorization of access to the cluster.
The operator may set up lists of permitted users who may act as administrators and
as clients of the cluster. Combined with the strong authentication feature described
above, this can enable a secure environment for some use cases. Note that fine-grained
access control (e.g. table-level or column-level) is not yet supported.</p>
</li>
<li>
<p>Kudu 1.3 adds a background task to tablet servers which removes historical versions of
data which have fallen behind the configured data retention time. This reduces disk space
usage in all workloads, but particularly in those with a higher volume of updates or
upserts.</p>
</li>
<li>
<p>Kudu now incorporates Google Breakpad, a library which writes crash reports in
the case of a server crash. These reports can be found within the configured log directory,
and can be useful during bug diagnosis.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_optimizations_and_improvements_2"><a class="link" href="#_optimizations_and_improvements_2">Optimizations and improvements</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Kudu servers will now change the file permissions of data directories and contained
data files based on a new configuration flag <code>--umask</code>. As a result, after upgrading,
permissions on disk may be more restrictive than in previous versions. The new default
configuration improves data security.</p>
</li>
<li>
<p>Kudu&#8217;s web UI will now redact strings which may include sensitive user data. For example,
the monitoring page which shows in-progress scans no longer includes the scanner predicate
values. The tracing and RPC diagnostics endpoints no longer include contents of RPCs which
may include table data.</p>
</li>
<li>
<p>By default, Kudu now reserves 1% of each configured data volume as free space. If a volume
is seen to have less than 1% of disk space free, Kudu will stop writing to that volume
to avoid completely filling up the disk.</p>
</li>
<li>
<p>The default encoding for numeric columns (int, float, and double) has been changed
to <code>BIT_SHUFFLE</code>. The default encoding for binary and string columns has been
changed to <code>DICT_ENCODING</code>. Dictionary encoding automatically falls back to the old
default (<code>PLAIN</code>) when cardinality is too high to be effectively encoded.</p>
<div class="paragraph">
<p>These new defaults match the default behavior of other storage mechanisms such as
Apache Parquet and are likely to perform better out of the box.</p>
</div>
</li>
<li>
<p>Kudu now uses <code>LZ4</code> compression when writing its Write Ahead Log (WAL). This improves
write performance and stability for many use cases.</p>
</li>
<li>
<p>Kudu now uses <code>LZ4</code> compression when writing delta files. This can improve both
read and write performance as well as save substantial disk usage, especially
for workloads involving a high number of updates or upserts containing compressible
data.</p>
</li>
<li>
<p>The Kudu API now supports the ability to express <code>IS NULL</code> and <code>IS NOT NULL</code> predicates
on scanners. The Spark DataSource integration will take advantage of these new
predicates when possible.</p>
</li>
<li>
<p>Both C++ and Java clients have been optimized to prune partitions more effectively
when performing scans using the <code>IN (&#8230;&#8203;)</code> predicate.</p>
</li>
<li>
<p>The exception messages produced by the Java client are now truncated to a maximum length
of 32KB.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.3.0_fixed_issues"><a class="link" href="#rn_1.3.0_fixed_issues">Fixed Issues</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1893">KUDU-1893</a>
Fixed a critical bug in which wrong results would be returned when evaluating
predicates applied to columns added using the <code>ALTER TABLE</code> operation.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1905">KUDU-1905</a>
Fixed a crash after inserting a row sharing a primary key with a recently-deleted
row in tables where the primary key is comprised of all of the columns.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1899">KUDU-1899</a>
Fixed a crash after inserting a row with an empty string as the single-column
primary key.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1904">KUDU-1904</a>
Fixed a potential crash when performing random reads against a column using RLE
encoding and containing long runs of NULL values.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1853">KUDU-1853</a>
Fixed an issue where disk space could be leaked on servers which experienced an error
during the process of copying tablet data from another server.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1856">KUDU-1856</a>
Fixed an issue in which disk space could be leaked by Kudu servers storing data on
partitions using the XFS file system. Any leaked disk space will be automatically
recovered upon upgrade.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1888">KUDU-1888</a>,
<a href="https://issues.apache.org/jira/browse/KUDU-1906">KUDU-1906</a>
Fixed multiple issues in the Java client where operation callbacks would never be
triggered, causing the client to hang.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.3.0_wire_compatibility"><a class="link" href="#rn_1.3.0_wire_compatibility">Wire Protocol compatibility</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 1.3.0 is wire-compatible with previous versions of Kudu:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Kudu 1.3 clients may connect to servers running Kudu 1.0. If the client uses features
that are not available on the target server, an error will be returned.</p>
</li>
<li>
<p>Kudu 1.0 clients may connect to servers running Kudu 1.3 with the exception of the
below-mentioned restrictions regarding secure clusters.</p>
</li>
<li>
<p>Rolling upgrade between Kudu 1.2 and Kudu 1.3 servers is believed to be possible
though has not been sufficiently tested. Users are encouraged to shut down all nodes
in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>The authentication features newly introduced in Kudu 1.3 place the following limitations
on wire compatibility with older versions:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>If a Kudu 1.3 cluster is configured with authentication or encryption set to "required",
older clients will be unable to connect.</p>
</li>
<li>
<p>If a Kudu 1.3 cluster is configured with authentication and encryption set to "optional"
or "disabled", older clients will still be able to connect.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.3.0_incompatible_changes"><a class="link" href="#rn_1.3.0_incompatible_changes">Incompatible Changes in Kudu 1.3.0</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Due to storage format changes in Kudu 1.3, downgrade from Kudu 1.3 to earlier versions
is not supported. After upgrading to Kudu 1.3, attempting to restart with an earlier
version will result in an error.</p>
</li>
<li>
<p>In order to support running MapReduce and Spark jobs on secure clusters, these
frameworks now connect to the cluster at job submission time to retrieve authentication
credentials which can later be used by the tasks to be spawned. This means that
the process submitting jobs to Kudu clusters must have direct access to that cluster.</p>
</li>
<li>
<p>The embedded web servers in Kudu processes now specify the <code>X-Frame-Options: DENY</code> HTTP
header which prevents embedding Kudu web pages in HTML <code>iframe</code> elements.</p>
</li>
</ul>
</div>
<div class="sect2">
<h3 id="rn_1.3.0_client_compatibility"><a class="link" href="#rn_1.3.0_client_compatibility">Client Library Compatibility</a></h3>
<div class="ulist">
<ul>
<li>
<p>The Kudu 1.3 Java client library is API- and ABI-compatible with Kudu 1.2. Applications
written against Kudu 1.2 will compile and run against the Kudu 1.3 client library and
vice-versa, unless one of the following newly added APIs is used:</p>
<div class="ulist">
<ul>
<li>
<p><code>[Async]KuduClient.exportAuthenticationCredentials(&#8230;&#8203;)</code> (unstable API)</p>
</li>
<li>
<p><code>[Async]KuduClient.importAuthenticationCredentials(&#8230;&#8203;)</code> (unstable API)</p>
</li>
<li>
<p><code>[Async]KuduClient.getMasterAddressesAsString()</code></p>
</li>
<li>
<p><code>KuduPredicate.newIsNotNullPredicate()</code></p>
</li>
<li>
<p><code>KuduPredicate.newIsNullPredicate()</code></p>
</li>
</ul>
</div>
</li>
<li>
<p>The Kudu 1.3 C++ client is API- and ABI-forward-compatible with Kudu 1.2.
Applications written and compiled against the Kudu 1.2 client library will run without
modification against the Kudu 1.3 client library. Applications written and compiled
against the Kudu 1.3 client library will run without modification against the Kudu 1.2
client library unless they use one of the following new APIs:</p>
<div class="ulist">
<ul>
<li>
<p><code>kudu::DisableOpenSSLInitialization()</code></p>
</li>
<li>
<p><code>KuduClientBuilder::import_authentication_credentials(&#8230;&#8203;)</code></p>
</li>
<li>
<p><code>KuduClient::ExportAuthenticationCredentials(&#8230;&#8203;)</code></p>
</li>
<li>
<p><code>KuduClient::NewIsNotNullPredicate(&#8230;&#8203;)</code></p>
</li>
<li>
<p><code>KuduClient::NewIsNullPredicate(&#8230;&#8203;)</code></p>
</li>
</ul>
</div>
</li>
<li>
<p>The Kudu 1.3 Python client is API-compatible with Kudu 1.2. Applications
written against Kudu 1.2 will continue to run against the Kudu 1.3 client
and vice-versa.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.2.0"><a class="link" href="#rn_1.2.0">Release notes specific to 1.2.0</a></h2>
<div class="sectionbody">
</div>
</div>
<div class="sect1">
<h2 id="rn_1.2.0_new_features"><a class="link" href="#rn_1.2.0_new_features">New features</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Kudu clients and servers now redact user data such as cell values
from log messages, Java exception messages, and <code>Status</code> strings.
User metadata such as table names, column names, and partition
bounds are not redacted.</p>
<div class="paragraph">
<p>Redaction is enabled by default, but may be disabled by setting the new
<code>log_redact_user_data</code> flag to <code>false</code>.</p>
</div>
</li>
<li>
<p>Kudu&#8217;s ability to provide consistency guarantees has been substantially
improved:</p>
<div class="ulist">
<ul>
<li>
<p>Replicas now correctly track their "safe timestamp". This timestamp
is the maximum timestamp at which reads are guaranteed to be
repeatable.</p>
</li>
<li>
<p>A scan created using the <code>SCAN_AT_SNAPSHOT</code> mode will now
either wait for the requested snapshot to be "safe" at the replica
being scanned, or be re-routed to a replica where the requested
snapshot is "safe". This ensures that all such scans are repeatable.</p>
</li>
<li>
<p>Kudu Tablet Servers now properly retain historical data when a row
with a given primary key is inserted and deleted, followed by the
insertion of a new row with the same key. Previous versions of Kudu
would not retain history in such situations. This allows the server
to return correct results for snapshot scans with a timestamp in the
past, even in the presence of such "reinsertion" scenarios.</p>
</li>
<li>
<p>The Kudu clients now automatically retain the timestamp of their latest
successful read or write operation. Scans using the <code>READ_AT_SNAPSHOT</code> mode
without a client-provided timestamp automatically assign a timestamp
higher than the timestamp of their most recent write. Writes also propagate
the timestamp, ensuring that sequences of operations with causal dependencies
between them are assigned increasing timestamps. Together, these changes
allow clients to achieve read-your-writes consistency, and also ensure
that snapshot scans performed by other clients return causally-consistent
results.</p>
</li>
</ul>
</div>
</li>
<li>
<p>Kudu servers now automatically limit the number of log files.
The number of log files retained can be configured using the
<code>max_log_files</code> flag. By default, 10 log files will be retained
at each severity level.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_optimizations_and_improvements_3"><a class="link" href="#_optimizations_and_improvements_3">Optimizations and improvements</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>The logging in the Java and C++ clients has been substantially quieted.
Clients no longer log messages in normal operation unless there
is some kind of error.</p>
</li>
<li>
<p>The C++ client now includes a <code>KuduSession::SetErrorBufferSpace</code>
API which can limit the amount of memory used to buffer
errors from asynchronous operations.</p>
</li>
<li>
<p>The Java client now fetches tablet locations from the Kudu Master
in batches of 1000, increased from batches of 10 in prior versions.
This can substantially improve the performance of Spark and Impala
queries running against Kudu tables with large numbers of tablets.</p>
</li>
<li>
<p>Table metadata lock contention in the Kudu Master was substantially
reduced. This improves the performance of tablet location lookups on
large clusters with a high degree of concurrency.</p>
</li>
<li>
<p>Lock contention in the Kudu Tablet Server during high-concurrency
write workloads was also reduced. This can reduce CPU consumption and
improve performance when a large number of concurrent clients are writing
to a smaller number of a servers.</p>
</li>
<li>
<p>Lock contention when writing log messages has been substantially reduced.
This source of contention could cause high tail latencies on requests,
and when under high load could contribute to cluster instability
such as election storms and request timeouts.</p>
</li>
<li>
<p>The <code>BITSHUFFLE</code> column encoding has been optimized to use the <code>AVX2</code>
instruction set present on processors including Intel&#174; Sandy Bridge
and later. Scans on <code>BITSHUFFLE</code>-encoded columns are now up to 30% faster.</p>
</li>
<li>
<p>The <code>kudu</code> tool now accepts hyphens as an alternative to underscores
when specifying actions. For example, <code>kudu local-replica copy-from-remote</code>
may be used as an alternative to <code>kudu local_replica copy_from_remote</code>.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.2.0_fixed_issues"><a class="link" href="#rn_1.2.0_fixed_issues">Fixed Issues</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1508">KUDU-1508</a>
Fixed a long-standing issue in which running Kudu on <code>ext4</code> file systems
could cause file system corruption.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1399">KUDU-1399</a>
Implemented an LRU cache for open files, which prevents running out of
file descriptors on long-lived Kudu clusters. By default, Kudu will
limit its file descriptor usage to half of its configured <code>ulimit</code>.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/5192">Gerrit #5192</a>
Fixed an issue which caused data corruption and crashes in the case that
a table had a non-composite (single-column) primary key, and that column
was specified to use <code>DICT_ENCODING</code> or <code>BITSHUFFLE</code> encodings. If a
table with an affected schema was written in previous versions of Kudu,
the corruption will not be automatically repaired; users are encouraged
to re-insert such tables after upgrading to Kudu 1.2 or later.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/5541">Gerrit #5541</a>
Fixed a bug in the Spark <code>KuduRDD</code> implementation which could cause
rows in the result set to be silently skipped in some cases.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1551">KUDU-1551</a>
Fixed an issue in which the tablet server would crash on restart in the
case that it had previously crashed during the process of allocating
a new WAL segment.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1764">KUDU-1764</a>
Fixed an issue where Kudu servers would leak approximately 16-32MB of disk
space for every 10GB of data written to disk. After upgrading to Kudu
1.2 or later, any disk space leaked in previous versions will be
automatically recovered on startup.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1750">KUDU-1750</a>
Fixed an issue where the API to drop a range partition would drop any
partition with a matching lower <em>or</em> upper bound, rather than any partition
with matching lower <em>and</em> upper bound.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1766">KUDU-1766</a>
Fixed an issue in the Java client where equality predicates which compared
an integer column to its maximum possible value (e.g. <code>Integer.MAX_VALUE</code>)
would return incorrect results.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1780">KUDU-1780</a>
Fixed the <code>kudu-client</code> Java artifact to properly shade classes in the
<code>com.google.thirdparty</code> namespace. The lack of proper shading in prior
releases could cause conflicts with certain versions of Google Guava.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/5327">Gerrit #5327</a>
Fixed shading issues in the <code>kudu-flume-sink</code> Java artifact. The sink
now expects that Hadoop dependencies are provided by Flume, and properly
shades the Kudu client&#8217;s dependencies.</p>
</li>
<li>
<p>Fixed a few issues using the Python client library from Python 3.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.2.0_wire_compatibility"><a class="link" href="#rn_1.2.0_wire_compatibility">Wire Protocol compatibility</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 1.2.0 is wire-compatible with previous versions of Kudu:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Kudu 1.2 clients may connect to servers running Kudu 1.0. If the client uses features
that are not available on the target server, an error will be returned.</p>
</li>
<li>
<p>Kudu 1.0 clients may connect to servers running Kudu 1.2 without limitations.</p>
</li>
<li>
<p>Rolling upgrade between Kudu 1.1 and Kudu 1.2 servers is believed to be possible
though has not been sufficiently tested. Users are encouraged to shut down all nodes
in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.2.0_incompatible_changes"><a class="link" href="#rn_1.2.0_incompatible_changes">Incompatible Changes in Kudu 1.2.0</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>The replication factor of tables is now limited to a maximum of 7. In addition,
it is no longer allowed to create a table with an even replication factor.</p>
</li>
<li>
<p>The <code>GROUP_VARINT</code> encoding is now deprecated. Kudu servers have never supported
this encoding, and now the client-side constant has been deprecated to match the
server&#8217;s capabilities.</p>
</li>
</ul>
</div>
<div class="sect2">
<h3 id="_new_restrictions_on_data_schemas_and_identifiers"><a class="link" href="#_new_restrictions_on_data_schemas_and_identifiers">New Restrictions on Data, Schemas, and Identifiers</a></h3>
<div class="paragraph">
<p>Kudu 1.2.0 introduces several new restrictions on schemas, cell size, and identifiers:</p>
</div>
<div class="dlist">
<dl>
<dt class="hdlist1">Number of Columns</dt>
<dd>
<p>By default, Kudu will not permit the creation of tables with
more than 300 columns. We recommend schema designs that use fewer columns for best
performance.</p>
</dd>
<dt class="hdlist1">Size of Cells</dt>
<dd>
<p>No individual cell may be larger than 64KB. The cells making up a
a composite key are limited to a total of 16KB after the internal composite-key encoding
done by Kudu. Inserting rows not conforming to these limitations will result in errors
being returned to the client.</p>
</dd>
<dt class="hdlist1">Valid Identifiers</dt>
<dd>
<p>Identifiers such as column and table names are now restricted to
be valid UTF-8 strings. Additionally, a maximum length of 256 characters is enforced.</p>
</dd>
</dl>
</div>
</div>
<div class="sect2">
<h3 id="rn_1.2.0_client_compatibility"><a class="link" href="#rn_1.2.0_client_compatibility">Client Library Compatibility</a></h3>
<div class="ulist">
<ul>
<li>
<p>The Kudu 1.2 Java client is API- and ABI-compatible with Kudu 1.1. Applications
written against Kudu 1.1 will compile and run against the Kudu 1.2 client and
vice-versa.</p>
</li>
<li>
<p>The Kudu 1.2 C++ client is API- and ABI-forward-compatible with Kudu 1.1.
Applications written and compiled against the Kudu 1.1 client will run without
modification against the Kudu 1.2 client. Applications written and compiled
against the Kudu 1.2 client will run without modification against the Kudu 1.1
client unless they use one of the following new APIs:</p>
<div class="ulist">
<ul>
<li>
<p><code>kudu::DisableSaslInitialization()</code></p>
</li>
<li>
<p><code>KuduSession::SetErrorBufferSpace(&#8230;&#8203;)</code></p>
</li>
</ul>
</div>
</li>
<li>
<p>The Kudu 1.2 Python client is API-compatible with Kudu 1.1. Applications
written against Kudu 1.1 will continue to run against the Kudu 1.2 client
and vice-versa.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.1.0"><a class="link" href="#rn_1.1.0">Release notes specific to 1.1.0</a></h2>
<div class="sectionbody">
</div>
</div>
<div class="sect1">
<h2 id="rn_1.1.0_new_features"><a class="link" href="#rn_1.1.0_new_features">New features</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>The Python client has been brought up to feature parity with the Java and C++ clients
and as such the package version will be brought to 1.1 with this release (from 0.3). A
list of the highlights can be found below.</p>
<div class="ulist">
<ul>
<li>
<p>Improved Partial Row semantics</p>
</li>
<li>
<p>Range partition support</p>
</li>
<li>
<p>Scan Token API</p>
</li>
<li>
<p>Enhanced predicate support</p>
</li>
<li>
<p>Support for all Kudu data types (including a mapping of Python&#8217;s <code>datetime.datetime</code> to
<code>UNIXTIME_MICROS</code>)</p>
</li>
<li>
<p>Alter table support</p>
</li>
<li>
<p>Enabled Read at Snapshot for Scanners</p>
</li>
<li>
<p>Enabled Scanner Replica Selection</p>
</li>
<li>
<p>A few bug fixes for Python 3 in addition to various other improvements.</p>
</li>
</ul>
</div>
</li>
<li>
<p>IN LIST predicate pushdown support was added to allow optimized execution of filters which
match on a set of column values. Support for Spark, Map Reduce and Impala queries utilizing
IN LIST pushdown is not yet complete.</p>
</li>
<li>
<p>The Java client now features client-side request tracing in order to help troubleshoot timeouts.
Error messages are now augmented with traces that show which servers were contacted before the
timeout occurred instead of just the last error. The traces also contain RPCs that were
required to fulfill the client&#8217;s request, such as contacting the master to discover a tablet&#8217;s
location. Note that the traces are not available for successful requests and are not
programmatically queryable.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_optimizations_and_improvements_4"><a class="link" href="#_optimizations_and_improvements_4">Optimizations and improvements</a></h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Kudu now publishes JAR files for Spark 2.0 compiled with Scala 2.11 along with the
existing Spark 1.6 JAR compiled with Scala 2.10.</p>
</li>
<li>
<p>The Java client now allows configuring scanners to read from the closest replica instead of
the known leader replica. The default remains the latter. Use the relevant <code>ReplicaSelection</code>
enum with the scanner&#8217;s builder to change this behavior.</p>
</li>
<li>
<p>Tablet servers use a new policy for retaining write-ahead log (WAL) segments.
Previously, servers used the 'log_min_segments_to_retain' flag to prioritize
any flushes which were retaining log segments past the configured value (default 2).
This policy caused servers to flush in-memory data more frequently than necessary,
limiting write performance.</p>
<div class="paragraph">
<p>The new policy introduces a new flag 'log_target_replay_size_mb' which
determines the threshold at which write-ahead log retention will prioritize flushes.
The new flag is considered experimental and users should not need to modify
its value.</p>
</div>
<div class="paragraph">
<p>The improved policy has been seen to improve write performance in some use cases
by a factor of 2x relative to the old policy.</p>
</div>
</li>
<li>
<p>Kudu&#8217;s implementation of the Raft consensus algorithm has been improved to include
a "pre-election" phase. This can improve the stability of tablet leader election
in high-load scenarios, especially if each server hosts a high number of tablets.</p>
</li>
<li>
<p>Tablet server start-up time has been substantially improved in the case that
the server contains a high number of tombstoned tablet replicas.</p>
</li>
</ul>
</div>
<div class="sect2">
<h3 id="_command_line_tools"><a class="link" href="#_command_line_tools">Command line tools</a></h3>
<div class="ulist">
<ul>
<li>
<p>The tool <code>kudu tablet leader_step_down</code> has been added to manually force a leader to step down.</p>
</li>
<li>
<p>The tool <code>kudu remote_replica copy</code> has been added to manually copy a replica from
one running tablet server to another.</p>
</li>
<li>
<p>The tool <code>kudu local_replica delete</code> has been added to delete a replica of a tablet.</p>
</li>
<li>
<p>The <code>kudu test loadgen</code> tool has been added to replace the obsoleted
<code>insert-generated-rows</code> standalone binary. The new tool is enriched with
additional functionality and can be used to run load generation tests against
a Kudu cluster.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_wire_protocol_compatibility"><a class="link" href="#_wire_protocol_compatibility">Wire protocol compatibility</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 1.1.0 is wire-compatible with previous versions of Kudu:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Kudu 1.1 clients may connect to servers running Kudu 1.0. If the client uses the new
'IN LIST' predicate type, an error will be returned.</p>
</li>
<li>
<p>Kudu 1.0 clients may connect to servers running Kudu 1.1 without limitations.</p>
</li>
<li>
<p>Rolling upgrade between Kudu 1.0 and Kudu 1.1 servers is believed to be possible
though has not been sufficiently tested. Users are encouraged to shut down all nodes
in the cluster, upgrade the software, and then restart the daemons on the new version.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.1.0_incompatible_changes"><a class="link" href="#rn_1.1.0_incompatible_changes">Incompatible changes in Kudu 1.1.0</a></h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_client_apis_c_java_python"><a class="link" href="#_client_apis_c_java_python">Client APIs (C++/Java/Python)</a></h3>
<div class="ulist">
<ul>
<li>
<p>The C++ client no longer requires the
<a href="https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html">old gcc5 ABI</a>.
Which ABI is actually used depends on the compiler configuration. Some new distros
(e.g. Ubuntu 16.04) will use the new ABI. Your application must use the same ABI as is
used by the client library; an easy way to guarantee this is to use the same compiler
to build both.</p>
</li>
<li>
<p>The C++ client&#8217;s <code>KuduSession::CountBufferedOperations()</code> method is
deprecated. Its behavior is inconsistent unless the session runs in the
<code>MANUAL_FLUSH</code> mode. Instead, to get number of buffered operations, count
invocations of the <code>KuduSession::Apply()</code> method since last
<code>KuduSession::Flush()</code> call or, if using asynchronous flushing, since last
invocation of the callback passed into <code>KuduSession::FlushAsync()</code>.</p>
</li>
<li>
<p>The Java client&#8217;s <code>OperationResponse.getWriteTimestamp</code> method was renamed to <code>getWriteTimestampRaw</code>
to emphasize that it doesn&#8217;t return milliseconds, unlike what its Javadoc indicated. The renamed
method was also hidden from the public APIs and should not be used.</p>
</li>
<li>
<p>The Java client&#8217;s sync API (<code>KuduClient</code>, <code>KuduSession</code>, <code>KuduScanner</code>) used to throw either
a <code>NonRecoverableException</code> or a <code>TimeoutException</code> for a timeout, and now it&#8217;s only possible for the
client to throw the former.</p>
</li>
<li>
<p>The Java client&#8217;s handling of errors in <code>KuduSession</code> was modified so that subclasses of
<code>KuduException</code> are converted into RowErrors instead of being thrown.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.0.1"><a class="link" href="#rn_1.0.1">Release notes specific to 1.0.1</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Apache Kudu 1.0.1 is a bug fix release, with no new features or backwards
incompatible changes.</p>
</div>
<div class="sect2">
<h3 id="rn_1.0.1_fixed_issues"><a class="link" href="#rn_1.0.1_fixed_issues">Fixed Issues</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1681">KUDU-1681</a> Fixed a bug in
the tablet server which could cause a crash when the DNS lookup during master
heartbeat failed.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1660">KUDU-1660</a>: Fixed a bug
which would cause the Kudu master and tablet server to fail to start on single
CPU systems.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1651">KUDU-1652</a>: Fixed a bug
that would cause the C++ client, tablet server, and Java client to crash or
throw an exception when attempting to scan a table with a predicate which
simplifies to <code>IS NOT NULL</code> on a non-nullable column. For instance, setting a
<code>&#8656; 127</code> predicate on an <code>INT8</code> column could trigger this bug, since the
predicate only filters null values.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1651">KUDU-1651</a>: Fixed a bug
that would cause the tablet server to crash when evaluating a scan with
predicates over a dictionary encoded column containing an entire block of null
values.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1623">KUDU-1623</a>: Fixed a bug
that would cause the tablet server to crash when handling UPSERT operations
that only set values for the primary key columns.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/4488">Gerrit #4488</a> Fixed a bug in the
Java client&#8217;s KuduException class which could cause an unexpected
NullPointerException to be thrown when the exception did not have an
associated message.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1090">KUDU-1090</a> Fixed a bug in
the memory tracker which could cause a rare crash during tablet server
startup.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_1.0.0"><a class="link" href="#rn_1.0.0">Release notes specific to 1.0.0</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>After approximately a year of beta releases, Apache Kudu has reached version 1.0.
This version number signifies that the development team feels that Kudu is stable
enough for usage in production environments.</p>
</div>
<div class="paragraph">
<p>If you are new to Kudu, check out its list of <a href="index.html">features and benefits</a>.</p>
</div>
<div class="sect2">
<h3 id="rn_1.0.0_new_features"><a class="link" href="#rn_1.0.0_new_features">New features</a></h3>
<div class="paragraph">
<p>Kudu 1.0.0 delivers a number of new features, bug fixes, and optimizations.</p>
</div>
<div class="ulist">
<ul>
<li>
<p>Removal of multiversion concurrency control (MVCC) history is now supported.
This is known as tablet history GC. This allows Kudu to reclaim disk space,
where previously Kudu would keep a full history of all changes made to a
given table since the beginning of time. Previously, the only way to reclaim
disk space was to drop a table.</p>
<div class="paragraph">
<p>Kudu will still keep historical data, and the amount of history retained is
controlled by setting the configuration flag <code>--tablet_history_max_age_sec</code>,
which defaults to 15 minutes (expressed in seconds). The timestamp
represented by the current time minus <code>tablet_history_max_age_sec</code> is known
as the ancient history mark (AHM). When a compaction or flush occurs, Kudu
will remove the history of changes made prior to the ancient history mark.
This only affects historical data; currently-visible data will not be
removed. A specialized maintenance manager background task to remove existing
"cold" historical data that is not in a row affected by the normal compaction
process will be added in a future release.</p>
</div>
</li>
<li>
<p>Most of Kudu&#8217;s command line tools have been consolidated under a new
top-level <code>kudu</code> tool. This reduces the number of large binaries distributed
with Kudu and also includes much-improved help output.</p>
</li>
<li>
<p>The Kudu Flume Sink now supports processing events containing Avro-encoded
records, using the new <code>AvroKuduOperationsProducer</code>.</p>
</li>
<li>
<p>Administrative tools including <code>kudu cluster ksck</code> now support running
against multi-master Kudu clusters.</p>
</li>
<li>
<p>The output of the <code>ksck</code> tool is now colorized and much easier to read.</p>
</li>
<li>
<p>The C++ client API now supports writing data in <code>AUTO_FLUSH_BACKGROUND</code> mode.
This can provide higher throughput for ingest workloads.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="_optimizations_and_improvements_5"><a class="link" href="#_optimizations_and_improvements_5">Optimizations and improvements</a></h3>
<div class="ulist">
<ul>
<li>
<p>The performance of comparison predicates on dictionary-encoded columns has
been substantially optimized. Users are encouraged to use dictionary encoding
on any string or binary columns with low cardinality, especially if these
columns will be filtered with predicates.</p>
</li>
<li>
<p>The Java client is now able to prune partitions from scanners based on the
provided predicates. For example, an equality predicate on a hash-partitioned
column will now only access those tablets that could possibly contain matching
data. This is expected to improve performance for the Spark integration as well
as applications using the Java client API.</p>
</li>
<li>
<p>The performance of compaction selection in the tablet server has been
substantially improved. This can increase the efficiency of the background
maintenance threads and improve overall throughput of heavy write workloads.</p>
</li>
<li>
<p>The policy by which the tablet server retains write-ahead log (WAL) files has
been improved so that it takes into account other replicas of the tablet.
This should help mitigate the spurious eviction of tablet replicas on machines
that temporarily lag behind the other replicas.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="_wire_protocol_compatibility_2"><a class="link" href="#_wire_protocol_compatibility_2">Wire protocol compatibility</a></h3>
<div class="paragraph">
<p>Kudu 1.0.0 maintains client-server wire-compatibility with previous releases.
Applications using the Kudu client libraries may be upgraded either
before, at the same time, or after the Kudu servers.</p>
</div>
<div class="paragraph">
<p>Kudu 1.0.0 does <em>not</em> maintain server-server wire compatibility with previous
releases. Therefore, rolling upgrades between earlier versions of Kudu and
Kudu 1.0.0 are not supported.</p>
</div>
</div>
<div class="sect2">
<h3 id="rn_1.0.0_incompatible_changes"><a class="link" href="#rn_1.0.0_incompatible_changes">Incompatible changes in Kudu 1.0.0</a></h3>
<div class="sect3">
<h4 id="_command_line_tools_2"><a class="link" href="#_command_line_tools_2">Command line tools</a></h4>
<div class="ulist">
<ul>
<li>
<p>The <code>kudu-pbc-dump</code> tool has been removed. The same functionality is now
implemented as <code>kudu pbc dump</code>.</p>
</li>
<li>
<p>The <code>kudu-ksck</code> tool has been removed. The same functionality is now
implemented as <code>kudu cluster ksck</code>.</p>
</li>
<li>
<p>The <code>cfile-dump</code> tool has been removed. The same functionality is now
implemented as <code>kudu fs cfile dump</code>.</p>
</li>
<li>
<p>The <code>log-dump</code> tool has been removed. The same functionality is now
implemented as <code>kudu wal dump</code> and <code>kudu local_replica dump wals</code>.</p>
</li>
<li>
<p>The <code>kudu-admin</code> tool has been removed. The same functionality is now
implemented within <code>kudu table</code> and <code>kudu tablet</code>.</p>
</li>
<li>
<p>The <code>kudu-fs_dump</code> tool has been removed. The same functionality is now
implemented as <code>kudu fs dump</code>.</p>
</li>
<li>
<p>The <code>kudu-ts-cli</code> tool has been removed. The same functionality is now
implemented within <code>kudu master</code>, <code>kudu remote_replica</code>, and <code>kudu tserver</code>.</p>
</li>
<li>
<p>The <code>kudu-fs_list</code> tool has been removed and some similar useful
functionality has been moved under 'kudu local_replica'.</p>
</li>
</ul>
</div>
</div>
<div class="sect3">
<h4 id="_configuration_flags"><a class="link" href="#_configuration_flags">Configuration flags</a></h4>
<div class="ulist">
<ul>
<li>
<p>Some configuration flags are now marked as 'unsafe' and 'experimental'. Such flags
are disallowed by default. Users may access these flags by enabling the additional
flags <code>--unlock_unsafe_flags</code> and <code>--unlock_experimental_flags</code>. Usage of such flags
is not recommended, as the flags may be removed or modified with no deprecation period
and without notice in future Kudu releases.</p>
</li>
</ul>
</div>
</div>
<div class="sect3">
<h4 id="_client_apis_c_java_python_2"><a class="link" href="#_client_apis_c_java_python_2">Client APIs (C++/Java/Python)</a></h4>
<div class="ulist">
<ul>
<li>
<p>The <code>TIMESTAMP</code> column type has been renamed to <code>UNIXTIME_MICROS</code> in order to
reduce confusion between Kudu&#8217;s timestamp support and the timestamps supported
by other systems such as Apache Hive and Apache Impala (incubating). Existing
tables will automatically be updated to use the new name for the type.</p>
<div class="paragraph">
<p>Clients upgrading to the new client libraries must move to the new name for
the type. Clients using old client libraries will continue to operate using
the old type name, even when connected to clusters that have been
upgraded. Similarly, if clients are upgraded before servers, existing
timestamp columns will be available using the new type name.</p>
</div>
</li>
<li>
<p><code>KuduSession</code> methods in the C++ library are no longer advertised as thread-safe
to have one set of semantics for both C++ and Java Kudu client libraries.</p>
</li>
<li>
<p>The <code>KuduScanToken::TabletServers</code> method in the C++ library has been removed.
The same information can now be found in the KuduScanToken::tablet method.</p>
</li>
</ul>
</div>
</div>
<div class="sect3">
<h4 id="_apache_flume_integration"><a class="link" href="#_apache_flume_integration">Apache Flume Integration</a></h4>
<div class="ulist">
<ul>
<li>
<p>The <code>KuduEventProducer</code> interface used to process Flume events into Kudu operations
for the Kudu Flume Sink has changed, and has been renamed <code>KuduOperationsProducer</code>.
The existing `KuduEventProducer`s have been updated for the new interface, and have
been renamed similarly.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_0.10.0"><a class="link" href="#rn_0.10.0">Release notes specific to 0.10.0</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 0.10.0 delivers a number of new features, bug fixes, and optimizations,
detailed below.</p>
</div>
<div class="paragraph">
<p>Kudu 0.10.0 maintains wire-compatibility with previous releases, meaning
that applications using the Kudu client libraries may be upgraded either
before, at the same time, or after the Kudu servers. However, if you begin
using new features of Kudu 0.10.0 such as manually range-partitioned tables,
you must first upgrade all clients to this release.</p>
</div>
<div class="paragraph">
<p>This release does not maintain full Java API or ABI compatibility with
Kudu 0.9.x due to a package rename and some other small changes. See below for details.</p>
</div>
<div class="paragraph">
<p>See also <a href="https://issues.apache.org/jira/issues/?jql=project%20%3D%20KUDU%20AND%20status%20%3D%20Resolved
%20AND%20fixVersion%20%3D%200.10.0">JIRAs resolved
for Kudu 0.10.0</a> and <a href="https://github.com/apache/kudu/compare/0.9.1...0.10.0">Git
changes between 0.9.1 and 0.10.0</a>.</p>
</div>
<div class="paragraph">
<p>To upgrade to Kudu 0.10.0, see <a href="#rn_0.10.0_upgrade">[rn_0.10.0_upgrade]</a>.</p>
</div>
<div class="sect2">
<h3 id="rn_0.10.0_incompatible_changes"><a class="link" href="#rn_0.10.0_incompatible_changes">Incompatible changes and deprecated APIs in 0.10.0</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="http://gerrit.cloudera.org:8080/3737">Gerrit #3737</a> The Java client has been repackaged
under <code>org.apache.kudu</code> instead of <code>org.kududb</code>. Import statements for Kudu classes must
be modified in order to compile against 0.10.0. Wire compatibility is maintained.</p>
</li>
<li>
<p><a href="https://gerrit.cloudera.org/#/c/3055/">Gerrit #3055</a> The Java client&#8217;s
synchronous API methods now throw <code>KuduException</code> instead of <code>Exception</code>.
Existing code that catches <code>Exception</code> should still compile, but introspection of an
exception&#8217;s message may be impacted. This change was made to allow thrown exceptions to be
queried more easily using <code>KuduException.getStatus</code> and calling one of <code>Status&#8217;s methods.
For example, an operation that tries to delete a table that doesn&#8217;t exist would return a
`Status</code> that returns true when queried on <code>isNotFound()</code>.</p>
</li>
<li>
<p>The Java client&#8217;s <code>KuduTable.getTabletsLocations</code> set of methods is now
deprecated. Additionally, they now take an exclusive end partition key instead
of an inclusive key. Applications are encouraged to use the scan tokens API
instead of these methods in the future.</p>
</li>
<li>
<p>The C++ API for specifying split points on range-partitioned tables has been improved
to make it easier for callers to properly manage the ownership of the provided rows.</p>
<div class="paragraph">
<p>The <code>TableCreator::split_rows</code> API took a <code>vector&lt;const KuduPartialRow*&gt;</code>, which
made it very difficult for the calling application to do proper error handling with
cleanup when setting the fields of the <code>KuduPartialRow</code>. This API has been now been
deprecated and replaced by a new method <code>TableCreator::add_range_split</code> which allows
easier use of smart pointers for safe memory management.</p>
</div>
</li>
<li>
<p>The Java client&#8217;s internal buffering has been reworked. Previously, the number of
buffered write operations was constrained on a per-tablet-server basis. Now, the configured
maximum buffer size constrains the total number of buffered operations across all
tablet servers in the cluster. This provides a more consistent bound on the memory
usage of the client regardless of the size of the cluster to which it is writing.</p>
<div class="paragraph">
<p>This change can negatively affect the write performance of Java clients which rely on
buffered writes. Consider using the <code>setMutationBufferSpace</code> API to increase a
session&#8217;s maximum buffer size if write performance seems to be degraded after upgrading
to Kudu 0.10.0.</p>
</div>
</li>
<li>
<p>The "remote bootstrap" process used to copy a tablet replica from one host to
another has been renamed to "Tablet Copy". This resulted in the renaming of
several RPC metrics. Any users previously explicitly fetching or monitoring metrics
related to Remote Bootstrap should update their scripts to reflect the new names.</p>
</li>
<li>
<p>The SparkSQL datasource for Kudu no longer supports mode <code>Overwrite</code>. Users should
use the new <code>KuduContext.upsertRows</code> method instead. Additionally, inserts using the
datasource are now upserts by default. The older behavior can be restored by setting
the <code>operation</code> parameter to <code>insert</code>.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.10.0_new_features"><a class="link" href="#rn_0.10.0_new_features">New features</a></h3>
<div class="ulist">
<ul>
<li>
<p>Users may now manually manage the partitioning of a range-partitioned table.
When a table is created, the user may specify a set of range partitions that
do not cover the entire available key space. A user may add or drop range
partitions to existing tables.</p>
<div class="paragraph">
<p>This feature can be particularly helpful with time series workloads in which
new partitions can be created on an hourly or daily basis. Old partitions
may be efficiently dropped if the application does not need to retain historical
data past a certain point.</p>
</div>
<div class="paragraph">
<p>This feature is considered experimental for the 0.10 release. More details of
the new feature can be found in the accompanying
<a href="https://kudu.apache.org/2016/08/23/new-range-partitioning-features.html">blog post</a>.</p>
</div>
</li>
<li>
<p>Support for running Kudu clusters with multiple masters has been stabilized.
Users may start a cluster with three or five masters to provide fault tolerance
despite a failure of one or two masters, respectively.</p>
<div class="paragraph">
<p>Note that certain tools (e.g. <code>ksck</code>) are still lacking complete support for
multiple masters. These deficiencies will be addressed in a following release.</p>
</div>
</li>
<li>
<p>Kudu now supports the ability to reserve a certain amount of free disk space
in each of its configured data directories. If a directory&#8217;s free disk space
drops to less than the configured minimum, Kudu will stop writing to that
directory until space becomes available. If no space is available in any
configured directory, Kudu will abort.</p>
<div class="paragraph">
<p>This feature may be configured using the <code>fs_data_dirs_reserved_bytes</code> and
<code>fs_wal_dir_reserved_bytes</code> flags.</p>
</div>
</li>
<li>
<p>The Spark integration&#8217;s <code>KuduContext</code> now supports four new methods for writing to
Kudu tables: <code>insertRows</code>, <code>upsertRows</code>, <code>updateRows</code>, and <code>deleteRows</code>. These are
now the preferred way to write to Kudu tables from Spark.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.10.0_improvements"><a class="link" href="#rn_0.10.0_improvements">Improvements and optimizations</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1516">KUDU-1516</a> The <code>kudu-ksck</code> tool
has been improved and now detects problems such as when a tablet does not have
a majority of replicas on live tablet servers, or if those replicas aren’t in a
good state. Users who currently depend on the tool to detect inconsistencies may now see
failures when before they wouldn&#8217;t see any.</p>
</li>
<li>
<p><a href="https://gerrit.cloudera.org:8080/3477">Gerrit #3477</a> The way operations are buffered in
the Java client has been reworked. Previously, the session&#8217;s buffer size was set per tablet, meaning that a buffer
size of 1,000 for 10 tablets being written to allowed for 10,000 operations to be buffered at the
same time. With this change, all the tablets share one buffer, so users might need to set a
bigger buffer size in order to reach the same level of performance as before.</p>
</li>
<li>
<p><a href="https://gerrit.cloudera.org/#/c/3674/">Gerrit #3674</a> Added LESS and GREATER options for
column predicates.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1444">KUDU-1444</a> added support for passing
back basic per-scan metrics (e.g cache hit rate) from the server to the C++ client. See the
<code>KuduScanner::GetResourceMetrics()</code> API for detailed usage. This feature will be supported
in the Java client API in a future release.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1446">KUDU-1446</a> improved the order in
which the tablet server evaluates predicates, so that predicates on smaller columns
are evaluated first. This may improve performance on queries which apply predicates
on multiple columns of different sizes.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1398">KUDU-1398</a> improved the storage
efficiency of Kudu&#8217;s internal primary key indexes. This optimization should decrease space
usage and improve random access performance, particularly for workloads with lengthy
primary keys.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.10.0_fixed_issues"><a class="link" href="#rn_0.10.0_fixed_issues">Fixed Issues</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://gerrit.cloudera.org/#/c/3541/">Gerrit #3541</a> Fixed a problem in the Java client
whereby an RPC could be dropped when a connection to a tablet server or master was forcefully
closed on the server-side while RPCs to that server were in the process of being encoded.
The effect was that the RPC would not be sent, and users of the synchronous API would receive
a <code>TimeoutException</code>. Several other Java client bugs which could cause similar spurious timeouts
were also fixed in this release.</p>
</li>
<li>
<p><a href="https://gerrit.cloudera.org/<mark>/c/3724/">Gerrit #3724</a> Fixed a problem in the Java client
whereby an RPC could be dropped when a socket timeout was fired while that RPC was being sent to
a tablet server or master. This would manifest itself in the same way
<a href="https://gerrit.cloudera.org/</mark>/c/3541/">Gerrit #3541</a>.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1538">KUDU-1538</a> fixed a bug in which recycled
block identifiers could cause the tablet server to lose data. Following this bug fix, block
identifiers will no longer be reused.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.10.0_changes"><a class="link" href="#rn_0.10.0_changes">Other noteworthy changes</a></h3>
<div class="ulist">
<ul>
<li>
<p>This is the first release of Apache Kudu as a top-level (non-incubating)
project!</p>
</li>
<li>
<p>The default false positive rate for Bloom filters has been changed
from 1% to 0.01%. This will increase the space consumption of Bloom
filters by a factor of two (from approximately 10 bits per row to
approximately 20 bits per row). This is expected to substantially
improve the performance of random-write workloads at the cost of an
incremental increase in disk space usage.</p>
</li>
<li>
<p>The Kudu C++ client library now has Doxygen-based
<a href="http://kudu.apache.org/cpp-client-api/">API documentation</a>
available online.</p>
</li>
<li>
<p>Kudu now
<a href="http://kudu.apache.org/2016/06/17/raft-consensus-single-node.html">
uses the Raft consensus algorithm even for unreplicated tables</a>.
This change simplifies code and will also allow administrators to enable
replication on a previously-unreplicated table. This change is internal and
should not be visible to users.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_0.9.1"><a class="link" href="#rn_0.9.1">Release notes specific to 0.9.1</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 0.9.1 delivers incremental bug fixes over Kudu 0.9.0. It is fully compatible with
Kudu 0.9.0.</p>
</div>
<div class="paragraph">
<p>See also <a href="https://issues.apache.org/jira/issues/?jql=project%20%3D%20KUDU%20AND%20status%20%3D%20Resolved
%20AND%20fixVersion%20%3D%200.9.1">JIRAs resolved
for Kudu 0.9.1</a> and <a href="https://github.com/apache/kudu/compare/0.9.0...0.9.1">Git
changes between 0.9.0 and 0.9.1</a>.</p>
</div>
<div class="sect2">
<h3 id="rn_0.9.1_fixed_issues"><a class="link" href="#rn_0.9.1_fixed_issues">Fixed Issues</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1469">KUDU-1469</a> fixed a bug in
our Raft consensus implementation that could cause a tablet to stop making progress after a leader
election.</p>
</li>
<li>
<p><a href="https://gerrit.cloudera.org/#/c/3456/">Gerrit #3456</a> fixed a bug in which
servers under high load could store metric information in incorrect memory
locations, causing crashes or data corruption.</p>
</li>
<li>
<p><a href="https://gerrit.cloudera.org/#/c/3457/">Gerrit #3457</a> fixed a bug in which
errors from the Java client would carry an incorrect error message.</p>
</li>
<li>
<p>Several other small bug fixes were backported to improve stability.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_0.9.0"><a class="link" href="#rn_0.9.0">Release notes specific to 0.9.0</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 0.9.0 delivers incremental features, improvements, and bug fixes over the previous versions.</p>
</div>
<div class="paragraph">
<p>See also <a href="https://issues.apache.org/jira/issues/?jql=project%20%3D%20KUDU%20AND%20status%20%3D%20Resolved
%20AND%20fixVersion%20%3D%200.9.0">JIRAs resolved
for Kudu 0.9.0</a> and <a href="https://github.com/apache/kudu/compare/0.8.0...0.9.0">Git
changes between 0.8.0 and 0.9.0</a>.</p>
</div>
<div class="paragraph">
<p>To upgrade to Kudu 0.10.0, see <a href="#rn_0.9.0_upgrade">[rn_0.9.0_upgrade]</a>.</p>
</div>
<div class="sect2">
<h3 id="rn_0.9.0_incompatible_changes"><a class="link" href="#rn_0.9.0_incompatible_changes">Incompatible changes</a></h3>
<div class="ulist">
<ul>
<li>
<p>The <code>KuduTableInputFormat</code> command has changed the way in which it handles
scan predicates, including how it serializes predicates to the job configuration
object. The new configuration key is <code>kudu.mapreduce.encoded.predicate</code>. Clients
using the <code>TableInputFormatConfigurator</code> are not affected.</p>
</li>
<li>
<p>The <code>kudu-spark</code> sub-project has been renamed to follow naming conventions for
Scala. The new name is <code>kudu-spark_2.10</code>.</p>
</li>
<li>
<p>Default table partitioning has been removed. All tables must now be created
with explicit partitioning. Existing tables are unaffected. See the
<a href="schema_design.html#no_default_partitioning">schema design guide</a> for more
details.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.9.0_new_features"><a class="link" href="#rn_0.9.0_new_features">New features</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1002">KUDU-1002</a> Added support for
<code>UPSERT</code> operations, whereby a row is inserted if it does not already exist, but
updated if it does. Support for <code>UPSERT</code> is included in Java, C++, and Python APIs,
but not in Impala.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1306">KUDU-1306</a> Scan token API
for creating partition-aware scan descriptors. This API simplifies executing
parallel scans for clients and query engines.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/#/c/2848/">Gerrit 2848</a> Added a kudu datasource
for Spark. This datasource uses the Kudu client directly instead of
using the MapReduce API. Predicate pushdowns for <code>spark-sql</code> and Spark filters are
included, as well as parallel retrieval for multiple tablets and column projections.
See an example of <a href="developing.html#_kudu_integration_with_spark">Kudu integration with Spark</a>.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/#/c/2992/">Gerrit 2992</a> Added the ability
to update and insert from Spark using a Kudu datasource.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.9.0_improvements"><a class="link" href="#rn_0.9.0_improvements">Improvements</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1415">KUDU-1415</a> Added statistics in the Java
client such as the number of bytes written and the number of operations applied.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1451">KUDU-1451</a> Improved tablet server restart
time when the tablet server needs to clean up of a lot previously deleted tablets. Tablets are
now cleaned up after they are deleted.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.9.0_fixed_issues"><a class="link" href="#rn_0.9.0_fixed_issues">Fixed Issues</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-678">KUDU-678</a> Fixed a leak that happened during
DiskRowSet compactions where tiny blocks were still written to disk even if there were no REDO
records. With the default block manager, it usually resulted in block containers with thousands
of tiny blocks.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1437">KUDU-1437</a> Fixed a data corruption issue
that occured after compacting sequences of negative INT32 values in a column that
was configured with RLE encoding.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.9.0_changes"><a class="link" href="#rn_0.9.0_changes">Other noteworthy changes</a></h3>
<div class="paragraph">
<p>All Kudu clients have longer default timeout values, as listed below.</p>
</div>
<div class="ulist">
<div class="title">Java</div>
<ul>
<li>
<p>The default operation timeout and the default admin operation timeout
are now set to 30 seconds instead of 10.</p>
</li>
<li>
<p>The default socket read timeout is now 10 seconds instead of 5.</p>
</li>
</ul>
</div>
<div class="ulist">
<div class="title">C++</div>
<ul>
<li>
<p>The default admin timeout is now 30 seconds instead of 10.</p>
</li>
<li>
<p>The default RPC timeout is now 10 seconds instead of 5.</p>
</li>
<li>
<p>The default scan timeout is now 30 seconds instead of 15.</p>
</li>
<li>
<p>Some default settings related to I/O behavior during flushes and compactions have been changed:
The default for <code>flush_threshold_mb</code> has been increased from 64MB to 1000MB. The default
<code>cfile_do_on_finish</code> has been changed from <code>close</code> to <code>flush</code>.
<a href="http://getkudu.io/2016/04/26/ycsb.html">Experiments using YCSB</a> indicate that these
values will provide better throughput for write-heavy applications on typical server hardware.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_0.8.0"><a class="link" href="#rn_0.8.0">Release notes specific to 0.8.0</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 0.8.0 delivers incremental features, improvements, and bug fixes over the previous versions.</p>
</div>
<div class="paragraph">
<p>See also <a href="https://issues.apache.org/jira/issues/?jql=project%20%3D%20KUDU%20AND%20status%20%3D%20Resolved
%20AND%20fixVersion%20%3D%200.8.0">JIRAs resolved
for Kudu 0.8.0</a> and <a href="https://github.com/apache/kudu/compare/0.7.1...0.8.0">Git
changes between 0.7.1 and 0.8.0</a>.</p>
</div>
<div class="paragraph">
<p>To upgrade to Kudu 0.8.0, see <a href="installation.html#upgrade">Upgrade from 0.7.1 to 0.8.0</a>.</p>
</div>
<div class="sect2">
<h3 id="rn_0.8.0_incompatible_changes"><a class="link" href="#rn_0.8.0_incompatible_changes">Incompatible changes</a></h3>
<div class="ulist">
<ul>
<li>
<p>0.8.0 clients are not fully compatible with servers running Kudu 0.7.1 or lower.
In particular, scans that specify column predicates will fail. To work around this
issue, upgrade all Kudu servers before upgrading clients.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.8.0_new_features"><a class="link" href="#rn_0.8.0_new_features">New features</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-431">KUDU-431</a> A simple Flume
sink has been implemented.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.8.0_improvements"><a class="link" href="#rn_0.8.0_improvements">Improvements</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-839">KUDU-839</a> Java RowError now uses an enum error code.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/#/c/2138/">Gerrit 2138</a> The handling of
column predicates has been re-implemented in the server and clients.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1379">KUDU-1379</a> Partition pruning
has been implemented for C++ clients (but not yet for the Java client). This feature
allows you to avoid reading a tablet if you know it does not serve the row keys you are querying.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/#/c/2641">Gerrit 2641</a> Kudu now uses
<code>earliest-deadline-first</code> RPC scheduling and rejection. This changes the behavior
of the RPC service queue to prevent unfairness when processing a backlog of RPC
threads and to increase the likelihood that an RPC will be processed before it
can time out.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.8.0_fixed_issues"><a class="link" href="#rn_0.8.0_fixed_issues">Fixed Issues</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.cloudera.org/browse/KUDU-1337">KUDU-1337</a> Tablets from tables
that were deleted might be unnecessarily re-bootstrapped when the leader gets the
notification to delete itself after the replicas do.</p>
</li>
<li>
<p><a href="https://issues.cloudera.org/browse/KUDU-969">KUDU-969</a> If a tablet server
shuts down while compacting a rowset and receiving updates for it, it might immediately
crash upon restart while bootstrapping that rowset&#8217;s tablet.</p>
</li>
<li>
<p><a href="https://issues.cloudera.org/browse/KUDU-1354">KUDU-1354</a> Due to a bug in Kudu&#8217;s
MVCC implementation where row locks were released before the MVCC commit happened,
flushed data would include out-of-order transactions, triggering a crash on the
next compaction.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1322">KUDU-1322</a> The C++ client
now retries write operations if the tablet it is trying to reach has already been
deleted.</p>
</li>
<li>
<p><a href="http://gerrit.cloudera.org:8080/#/c/2571/">Gerrit 2571</a> Due to a bug in the
Java client, users were unable to close the <code>kudu-spark</code> shell because of
lingering non-daemon threads.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.8.0_changes"><a class="link" href="#rn_0.8.0_changes">Other noteworthy changes</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="http://gerrit.cloudera.org:8080/#/c/2239/">Gerrit 2239</a> The concept of "feature flags"
was introduced in order to manage compatibility between different
Kudu versions. One case where this is helpful is if a newer client attempts to use
a feature unsupported by the currently-running tablet server. Rather than receiving
a cryptic error, the user gets an error message that is easier to interpret.
This is an internal change for Kudu system developers and requires no action by
users of the clients or API.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_0.7.1"><a class="link" href="#rn_0.7.1">Release notes specific to 0.7.1</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 0.7.1 is a bug fix release for 0.7.0.</p>
</div>
<div class="sect2">
<h3 id="rn_0.7.1_fixed_issues"><a class="link" href="#rn_0.7.1_fixed_issues">Fixed Issues</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1325">KUDU-1325</a> fixes a tablet server crash that could
occur during table deletion. In some cases, while a table was being deleted, other replicas would
attempt to re-replicate tablets to servers that had already processed the deletion. This could
trigger a race condition that caused a crash.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1341">KUDU-1341</a> fixes a potential data corruption and
crash that could happen shortly after tablet server restarts in workloads that repeatedly delete
and re-insert rows with the same primary key. In most cases, this corruption affected only a single
replica and could be repaired by re-replicating from another.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1343">KUDU-1343</a> fixes a bug in the Java client that
occurs when a scanner has to scan multiple batches from one tablet and then start scanning from
another. In particular, this would affect any scans using the Java client that read large numbers
of rows from multi-tablet tables.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1345">KUDU-1345</a> fixes a bug where in some cases the
hybrid clock could jump backwards, resulting in a crash followed by an inability to
restart the affected tablet server.</p>
</li>
<li>
<p><a href="https://issues.apache.org/jira/browse/KUDU-1360">KUDU-1360</a> fixes a bug in the kudu-spark module
which prevented reading rows with <code>NULL</code> values.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_0.7.0"><a class="link" href="#rn_0.7.0">Release notes specific to 0.7.0</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 0.7.0 is the first release done as part of the Apache Incubator and includes a number
of changes, new features, improvements, and fixes.</p>
</div>
<div class="paragraph">
<p>See also <a href="https://issues.cloudera.org/issues/?jql=project%20%3D%20Kudu%20AND%20status%20in%20
(Resolved)%20AND%20fixVersion%20%3D%200.7.0%20ORDER%20BY%20key%20ASC">JIRAs resolved
for Kudu 0.7.0</a> and <a href="https://github.com/apache/kudu/compare/branch-0.6.0...branch-0.7.0">Git
changes between 0.6.0 and 0.7.0</a>.</p>
</div>
<div class="paragraph">
<p>The upgrade instructions can be found at <a href="installation.html#upgrade">Upgrade from 0.6.0 to 0.7.0</a>.</p>
</div>
<div class="sect2">
<h3 id="rn_0.7.0_incompatible_changes"><a class="link" href="#rn_0.7.0_incompatible_changes">Incompatible changes</a></h3>
<div class="ulist">
<ul>
<li>
<p>The C++ client includes a new API, <code>KuduScanBatch</code>, which performs better when a
large number of small rows are returned in a batch. The old API of <code>vector&lt;KuduRowResult&gt;</code>
is deprecated.</p>
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
This change is API-compatible but <strong>not</strong> ABI-compatible.
</td>
</tr>
</table>
</div>
</li>
<li>
<p>The default replication factor has been changed from 1 to 3. Existing tables will
continue to use the replication factor they were created with. Applications that create
tables may not work properly if they assume a replication factor of 1 and fewer than
3 replicas are available. To use the previous default replication factor, start the
master with the configuration flag <code>--default_num_replicas=1</code>.</p>
</li>
<li>
<p>The Python client has been completely rewritten, with a focus on improving code
quality and testing. The read path (scanners) has been improved by adding many of
the features already supported by the C++ and Java clients. The Python client is no
longer considered experimental.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.7.0_new_features"><a class="link" href="#rn_0.7.0_new_features">New features</a></h3>
<div class="ulist">
<ul>
<li>
<p>With the goal of Spark integration in mind, a new <code>kuduRDD</code> API has been added,
which wraps <code>newAPIHadoopRDD</code> and includes a default source for Spark SQL.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.7.0_improvements"><a class="link" href="#rn_0.7.0_improvements">Improvements</a></h3>
<div class="ulist">
<ul>
<li>
<p>The Java client includes new methods <code>countPendingErrors()</code> and
<code>getPendingErrors()</code> on <code>KuduSession</code>. These methods allow you to count and
retrieve outstanding row errors when configuring sessions with <code>AUTO_FLUSH_BACKGROUND</code>.</p>
</li>
<li>
<p>New server-level metrics allow you to monitor CPU usage and context switching.</p>
</li>
<li>
<p>Kudu now builds on RHEL 7, CentOS 7, and SLES 12. Extra instructions are included
for SLES 12.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.7.0_fixed_issues"><a class="link" href="#rn_0.7.0_fixed_issues">Fixed Issues</a></h3>
<div class="ulist">
<ul>
<li>
<p><a href="https://issues.cloudera.org/browse/KUDU-1288">KUDU-1288</a> fixes a severe file descriptor
leak, which could previously only be resolved by restarting the tablet server.</p>
</li>
<li>
<p><a href="https://issues.cloudera.org/browse/KUDU-1250">KUDU-1250</a> fixes a hang in the Java
client when processing an in-flight batch and the previous batch encountered an error.</p>
</li>
</ul>
</div>
</div>
<div class="sect2">
<h3 id="rn_0.7.0_changes"><a class="link" href="#rn_0.7.0_changes">Other noteworthy changes</a></h3>
<div class="ulist">
<ul>
<li>
<p>The file block manager&#8217;s performance was improved, but it is still not recommended for
real-world use.</p>
</li>
<li>
<p>The master now attempts to spread tablets more evenly across the cluster during
table creation. This has no impact on existing tables, but will improve the speed
at which under-replicated tablets are re-replicated after a tablet server failure.</p>
</li>
<li>
<p>All licensing documents have been modified to adhere to ASF guidelines.</p>
</li>
<li>
<p>Kudu now requires an out-of-tree build directory. Review the build instructions
for additional information.</p>
</li>
<li>
<p>The <code>C` client library is now explicitly built against the
link:https://gcc.gnu.org/onlinedocs/libstdc/manual/using_dual_abi.html[old gcc5 ABI].
If you use gcc5 to build a Kudu application, your application must use the old ABI
as well. This is typically achieved by defining the `_GLIBCXX_USE_CXX11_ABI</code> macro
at compile-time when building your application. For more information, see the
previous link and link:http://developerblog.redhat.com/2015/02/05/gcc5-and-the-c11-abi/.</p>
</li>
<li>
<p>The Python client is no longer considered experimental.</p>
</li>
</ul>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_0.6.0"><a class="link" href="#rn_0.6.0">Release notes specific to 0.6.0</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>The 0.6.0 release contains incremental improvements and bug fixes. The most notable
changes are:</p>
</div>
<div class="ulist">
<ul>
<li>
<p>The Java client&#8217;s CreateTableBuilder and AlterTableBuilder classes have been renamed
to CreateTableOptions and AlterTableOptions. Their methods now also return <code>this</code> objects,
allowing them to be used as builders.</p>
</li>
<li>
<p>The Java client&#8217;s AbstractKuduScannerBuilder#maxNumBytes() setter is now called
batchSizeBytes as is the corresponding property in AsyncKuduScanner. This makes it
consistent with the C++ client.</p>
</li>
<li>
<p>The "kudu-admin" tool can now list and delete tables via its new subcommands
"list_tables" and "delete_table &lt;table_name&gt;".</p>
</li>
<li>
<p>OSX is now supported for single-host development. Please consult its specific installation
instructions in <a href="installation.html#osx_from_source">OS X</a>.</p>
</li>
</ul>
</div>
</div>
</div>
<div class="sect1">
<h2 id="rn_0.5.0"><a class="link" href="#rn_0.5.0">Release Notes Specific to 0.5.0</a></h2>
<div class="sectionbody">
<div class="paragraph">
<p>Kudu 0.5.0 was the first public release. As such, no improvements or changes were
noted in its release notes.</p>
</div>
</div>
</div>
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