Defer reroute when starting shards #44539
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* Defer reroute when starting shards Today we reroute the cluster as part of the process of starting a shard, which runs at `URGENT` priority. In large clusters, rerouting may take some time to complete, and this means that a mere trickle of shard-started events can cause starvation for other, lower-priority, tasks that are pending on the master. However, it isn't really necessary to perform a reroute when starting a shard, as long as one occurs eventually. This commit removes the inline reroute from the process of starting a shard and replaces it with a deferred one that runs at `NORMAL` priority, avoiding starvation of higher-priority tasks. This may improve some of the situations related to elastic#42738 and elastic#42105. * Specific test case for followup priority setting We cannot set the priority in all InternalTestClusters because the deprecation warning makes some tests unhappy. This commit adds a specific test instead. * Checkstyle * Cluster state always changed here * Assert consistency of routing nodes * Restrict setting only to reasonable priorities
DaveCTurner
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>enhancement
:Distributed Coordination/Allocation
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Pinging @elastic/es-distributed |
The change in elastic#44433 introduces a state in which the cluster has no relocating shards but still has a pending reroute task which might start a shard relocation. `TransportSearchFailuresIT` failed on a PR build seemingly because it did not wait for this pending task to complete too, reporting more active shards than expected: 2> java.lang.AssertionError: Expected: <9> but: was <10> at __randomizedtesting.SeedInfo.seed([4057CA4301FE95FA:207EC88573747235]:0) at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18) at org.junit.Assert.assertThat(Assert.java:956) at org.junit.Assert.assertThat(Assert.java:923) at org.elasticsearch.search.basic.TransportSearchFailuresIT.testFailedSearchWithWrongQuery(TransportSearchFailuresIT.java:97) This commit addresses this failure by waiting until there are neither pending tasks nor shard relocations in progress.
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Today we reroute the cluster as part of the process of starting a shard, which
runs at
URGENTpriority. In large clusters, rerouting may take some time tocomplete, and this means that a mere trickle of shard-started events can cause
starvation for other, lower-priority, tasks that are pending on the master.
However, it isn't really necessary to perform a reroute when starting a shard,
as long as one occurs eventually. This commit removes the inline reroute from
the process of starting a shard and replaces it with a deferred one that runs
at
NORMALpriority, avoiding starvation of higher-priority tasks.Backport of #44433 to
7.x..