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[[release_notes]]
= Apache Kudu 1.16.0 Release Notes

:author: Kudu Team
:imagesdir: ./images
:icons: font
:toc: left
:toclevels: 3
:doctype: book
:backend: html5
:sectlinks:
:experimental:

[[rn_1.16.0_upgrade_notes]]
== Upgrade Notes

[[rn_1.16.0_deprecations]]
== Deprecations
* Support for Python 2.x and Python 3.4 and earlier is deprecated and may be
  removed in the next minor release.

[[rn_1.16.0_new_features]]
== New features

* Clients can now require authentication and encryption instead of depending on
  server-side settings
  (link:https://issues.apache.org/jira/browse/KUDU-1921[KUDU-1921]).

* Kudu Masters now automatically attempt to add themselves to an existing
  cluster if there is a healthy Raft quorum among Kudu Masters.

* A new tool `kudu master unsafe_rebuild` is added to reconstruct the master
  catalog from tablet metadata collected from tablet servers. This can be used
  in emergencies to restore access to tables when all masters are unavailable.

* A new tool `kudu table set_replication_factor` is added to alter the
  replication factor of a table. The tool immediately updates table metadata in
  the master, and the master will asynchronously effect the new replication
  factor. Progress can be monitored by running `ksck`.

* It’s now possible to require a minimum replication factor for a Kudu table.
  This can be achieved by customizing the setting for the newly introduced
  `--min_num_replicas` kudu-master’s flag. For example, setting
  `--min_num_replicas=3` enforces every newly created table to have at least 3
  replicas for each of its tablets, so there cannot be a data loss when just a
  single tablet server in the cluster fails irrecoverably. For the sake of
  backward compatibility, `--min_num_replicas` is set to 1 by default.

* It’s now possible to track startup progress on the `/startup` page on the web
  UI. There are also metrics added to track the overall server startup progress
  as well as the processing of the log block containers and starting of the
  tablets (link:https://issues.apache.org/jira/browse/KUDU-1959[KUDU-1959]).

* A new tool `kudu table add_column` is added to add columns to existing tables
  using the CLI
  (link:https://issues.apache.org/jira/browse/KUDU-3339[KUDU-3339]).

* A new tool `kudu tserver unregister` is added to remove a dead tablet server
  from the cluster without restarting the masters
  (link:https://issues.apache.org/jira/browse/KUDU-2915[KUDU-2915]).


[[rn_1.16.0_improvements]]
== Optimizations and improvements

* Kudu will now more aggressively fsync consensus-related metadata when metadata
  is configured to be on an XFS mount. This may lead to increased contention on
  the device that backs metadata, but will prevent corruption in the event of an
  outage (link:https://issues.apache.org/jira/browse/KUDU-2195[KUDU-2195]).

* A clearer message is logged when the Ranger subprocess crashes, to specify a
  problem with the Ranger client.

* Two new flags have been introduced for the `kudu table scan` and `kudu perf
  table_scan` CLI tools: `--row_count_only` and `--report_scanner_stats`. With
  these new flags, the above mentioned CLI tools allow to issue scan requests
  equivalent to running “SELECT COUNT(1) FROM <table_name>” from impala-shell.
  These new provisions are useful in detecting and troubleshooting scan
  performance issues.

* Added replica selection configuration knob for the `kudu table scan` and `kudu
  perf table_scan` CLI tools: it’s controlled by the `--replica_selection` flag.

* To improve security, the following flags are now marked as sensitive and will
  be redacted in the logs and WebUI when the redaction is enabled:
  ** `--webserver_private_key_file`
  ** `--webserver_private_key_password_cmd`
  ** `--webserver_password_file`

* The logic to select the effective time source when running with
  `--time_source=auto` has been updated. The `builtin` time source would be
  auto-selected if a Kudu server runs with `--time_source=auto` in an
  environment where the instance detector isn't aware of dedicated NTP servers
  AND the `--builtin_ntp_servers` flag is set to a valid value. Otherwise, if
  `--builtin_ntp_servers` flag is set to an empty or invalid value, the
  effective time source becomes `system` for platforms supporting the
  `get_ntptime()` API, otherwise the catch-all case selects the `system_unsync`
  as the time effective source.

* It is now possible to print or edit PBC files in batch using the `kudu pbc`
  CLI tool, and also to format its JSON input/output as “pretty”.

* Client connection timeout is now configurable in the Java client
  (link:https://issues.apache.org/jira/browse/KUDU-3240[KUDU-3240]).

* A new `/healthz` endpoint is now available on the kudu-master and tablet-server
  embedded web servers for liveness checks
  (link:https://issues.apache.org/jira/browse/KUDU-3308[KUDU-3308]).

* Hive Metastore URI is now logged to the console when connecting via `kudu hms`
  CLI tool (link:https://issues.apache.org/jira/browse/KUDU-3189[KUDU-3189]).

* It is now possible to start up a master when there is an additional master
  address present in the master addresses flag
  (link:https://issues.apache.org/jira/browse/KUDU-3311[KUDU-3311]).

* Table entity is now accessible in `KuduWriteOperation` in the C++ client,
  making understanding errors on the client side easier
  (link:https://issues.apache.org/jira/browse/KUDU-2623[KUDU-2623]).

* The rebalancer tool now doesn’t move replicas to tablet servers in maintenance
  mode (link:https://issues.apache.org/jira/browse/KUDU-3328[KUDU-3328]).

* Improved the performance of the run length encoding (RLE).

[[rn_1.16.0_fixed_issues]]
== Fixed Issues
* Log4J used in Ranger subprocess was upgraded to 2.17.1 which contains patches
  go several security vulnerabilities
  (link:https://nvd.nist.gov/vuln/detail/CVE-2021-44832[CVE-2021-44832],
  link:https://nvd.nist.gov/vuln/detail/CVE-2021-45105[CVE-2021-45105],
  link:https://nvd.nist.gov/vuln/detail/CVE-2021-45046[CVE-2021-45046], and
  link:https://nvd.nist.gov/vuln/detail/CVE-2021-44228[CVE-2021-44228]).

* Kudu servers previously crashed if hostnames became unresolvable via DNS (e.g.
  if the container hosting a server were destroyed). Such errors are now treated
  as transient and the lookups are retried periodically. See
  link:https://issues.apache.org/jira/browse/KUDU-75[KUDU-75],
  link:https://issues.apache.org/jira/browse/KUDU-1620[KUDU-1620],
  and link:https://issues.apache.org/jira/browse/KUDU-1885[KUDU-1885] for more details.

* Fixed an issue in Kudu Java client where concurrent flushing of data buffers
  could lead to errors reported as 'java.lang.AssertionError: This Deferred was
  already called'
  (link:https://issues.apache.org/jira/browse/KUDU-3277[KUDU-3277]).

* Fixed Kudu RPC negotiation issue when running with cyrus-sasl-gssapi-2.1.27-5
  and newer versions of the RPM package. A failed RPC connection negotiation
  attempt would result in an error logged along with the full connection
  negotiation trace: `Runtime error: SASL(-15): mechanism too weak for this
  user: Unable to find a callback: 32775`
  (link:https://issues.apache.org/jira/browse/KUDU-3297[KUDU-3297]).

* Fixed crash in kudu-master and kudu-tserver when running with kernel where the
  `getrandom(2)` API is not available (versions of Linux kernel prior to 3.17).

* Fixed bug which could lead to exhaustion of the address space for the outgoing
  connections on a busy Kudu cluster
  (link:https://issues.apache.org/jira/browse/KUDU-3352[KUDU-3352]).

* Fixed a bug in the Java client where a malformed tablet server ID in the scan
  token causes connection failures and timeouts in some cases
  (link:https://issues.apache.org/jira/browse/KUDU-3349[KUDU-3349]).

* Fixed a bug where the rebalancer failed with `-ignored_tservers` flag
  (link:https://issues.apache.org/jira/browse/KUDU-3346[KUDU-3346]).

[[rn_1.16.0_wire_compatibility]]
== Wire Protocol compatibility

Kudu 1.16.0 is wire-compatible with previous versions of Kudu:

* Kudu 1.16 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.
* Rolling upgrade between Kudu 1.15 and Kudu 1.16 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.
* Kudu 1.0 clients may connect to servers running Kudu 1.16 with the exception of the
  below-mentioned restrictions regarding secure clusters.

The authentication features introduced in Kudu 1.3 place the following limitations
on wire compatibility between Kudu 1.16 and versions earlier than 1.3:

* If a Kudu 1.16 cluster is configured with authentication or encryption set to "required",
  clients older than Kudu 1.3 will be unable to connect.
* If a Kudu 1.16 cluster is configured with authentication and encryption set to "optional"
  or "disabled", older clients will still be able to connect.

[[rn_1.16.0_incompatible_changes]]
== Incompatible Changes in Kudu 1.16.0

[[rn_1.16.0_client_compatibility]]
=== Client Library Compatibility

* The Kudu 1.16 Java client library is API- and ABI-compatible with Kudu 1.15. Applications
  written against Kudu 1.15 will compile and run against the Kudu 1.16 client library and
  vice-versa.

* The Kudu 1.16 {cpp} client is API- and ABI-forward-compatible with Kudu 1.15.
  Applications written and compiled against the Kudu 1.15 client library will run without
  modification against the Kudu 1.16 client library. Applications written and compiled
  against the Kudu 1.16 client library will run without modification against the Kudu 1.15
  client library.

* The Kudu 1.16 Python client is API-compatible with Kudu 1.15. Applications
  written against Kudu 1.15 will continue to run against the Kudu 1.16 client
  and vice-versa.

[[rn_1.16.0_known_issues]]
== Known Issues and Limitations

Please refer to the link:known_issues.html[Known Issues and Limitations] section of the
documentation.

[[rn_1.16.0_contributors]]
== Contributors

Kudu 1.16.0 includes contributions from 17 people, including 5 first-time contributors:

* Riza Suminto
* Zoltan Chovan
* kedeng
* khazarmammadli
* yejiabao

Thank you for your contributions!

[[resources_and_next_steps]]
== Resources

- link:http://kudu.apache.org[Kudu Website]
- link:http://github.com/apache/kudu[Kudu GitHub Repository]
- link:index.html[Kudu Documentation]
- link:prior_release_notes.html[Release notes for older releases]

== Installation Options

For full installation details, see link:installation.html[Kudu Installation].

== Next Steps
- link:quickstart.html[Kudu Quickstart]
- link:installation.html[Installing Kudu]
- link:configuration.html[Configuring Kudu]