Release note updates for 1.1
Change-Id: Ifa6bf79830d0b7fd2595d1ba64ea3673e90e5008
Reviewed-on: http://gerrit.cloudera.org:8080/5079
Reviewed-by: Jean-Daniel Cryans <jdcryans@apache.org>
Reviewed-by: Adar Dembo <adar@cloudera.com>
Tested-by: Kudu Jenkins
Tested-by: Todd Lipcon <todd@apache.org>
(cherry picked from commit b46c4ecf9826de35a2a68d7a18a9dfc117cd7613)
Reviewed-on: http://gerrit.cloudera.org:8080/5081
Reviewed-by: Todd Lipcon <todd@apache.org>
diff --git a/docs/release_notes.adoc b/docs/release_notes.adoc
index 7ca9b70..ccc5207 100644
--- a/docs/release_notes.adoc
+++ b/docs/release_notes.adoc
@@ -67,6 +67,27 @@
the known leader replica. The default remains the latter. Use the relevant `ReplicaSelection`
enum with the scanner's builder to change this behavior.
+* 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.
++
+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.
++
+The improved policy has been seen to improve write performance in some use cases
+ by a factor of 2x relative to the old policy.
+
+* Kudu'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.
+
+* Tablet server start-up time has been substantially improved in the case that
+ the server contains a high number of tombstoned tablet replicas.
+
=== Command line tools
* The tool `kudu tablet leader_step_down` has been added to manually force a leader to step down.
@@ -80,7 +101,14 @@
== Wire protocol compatibility
-XXX
+Kudu 1.1.0 is wire-compatible with previous versions of Kudu:
+
+* 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.
+* Kudu 1.0 clients may connect to servers running Kudu 1.1 without limitations.
+* 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.
[[rn_1.1.0_incompatible_changes]]
== Incompatible changes in Kudu 1.1.0
@@ -162,24 +190,12 @@
* Updates, inserts, and deletes via Impala are non-transactional. If a query
fails part of the way through, its partial effects will not be rolled back.
-* All queries will be distributed across all Impala hosts which host a replica
- of the target table(s), even if a predicate on a primary key could correctly
- restrict the query to a single tablet. This limits the maximum concurrency of
- short queries made via Impala.
-
* No timestamp and decimal type support.
* The maximum parallelism of a single query is limited to the number of tablets
in a table. For good analytic performance, aim for 10 or more tablets per host
or use large tables.
-* Impala is only able to push down predicates involving `=`, `<=`, `>=`,
- or `BETWEEN` comparisons between any column and a literal value, and `<` and `>`
- for integer columns only. For example, for a table with an integer key `ts`, and
- a string key `name`, the predicate `WHERE ts >= 12345` will convert into an
- efficient range scan, whereas `where name > 'lipcon'` will currently fetch all
- data from the table and evaluate the predicate within Impala.
-
=== Security Limitations
* Authentication and authorization features are not implemented.
