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Posted to dev@lucene.apache.org by "Scott Blum (JIRA)" <ji...@apache.org> on 2017/03/15 00:06:41 UTC
[jira] [Updated] (SOLR-10277) On 'downnode', lots of wasteful
mutations are done to ZK
[ https://issues.apache.org/jira/browse/SOLR-10277?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Scott Blum updated SOLR-10277:
------------------------------
Affects Version/s: 5.5.4
6.0.1
6.2.1
6.3
6.4.2
> On 'downnode', lots of wasteful mutations are done to ZK
> --------------------------------------------------------
>
> Key: SOLR-10277
> URL: https://issues.apache.org/jira/browse/SOLR-10277
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Affects Versions: 5.5.3, 5.5.4, 6.0.1, 6.2.1, 6.3, 6.4.2
> Reporter: Joshua Humphries
> Labels: leader, zookeeper
>
> When a node restarts, it submits a single 'downnode' message to the overseer's state update queue.
> When the overseer processes the message, it does way more writes to ZK than necessary. In our cluster of 48 hosts, the majority of collections have only 1 shard and 1 replica. So a single node restarting should only result in ~1/40th of the collections being updated with new replica states (to indicate the node that is no longer active).
> However, the current logic in NodeMutator#downNode always updates *every* collection. So we end up having to do rolling restarts very slowly to avoid having a severe outage due to the overseer having to do way too much work for each host that is restarted. And subsequent shards becoming leader can't get processed until the `downnode` message is fully processed. So a fast rolling restart can result in the overseer queue growing incredibly large and nearly all shards winding up in a leader-less state until that backlog is processed.
> The fix is a trivial logic change to only add a ZkWriteCommand for collections that actually have an impacted replica.
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