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https://issues.apache.org/jira/browse/SOLR-10720?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Shalin Shekhar Mangar reassigned SOLR-10720:
--------------------------------------------
Assignee: Shalin Shekhar Mangar
> Aggressive removal of a collection breaks cluster state
> -------------------------------------------------------
>
> Key: SOLR-10720
> URL: https://issues.apache.org/jira/browse/SOLR-10720
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Components: SolrCloud
> Affects Versions: 6.5.1
> Reporter: Alexey Serba
> Assignee: Shalin Shekhar Mangar
>
> We are periodically seeing tricky concurrency bug in SolrCloud that starts
> with `Could not fully remove collection: my_collection` exception:
> {noformat}
> 2017-05-17T14:47:50,153 - ERROR
> [OverseerThreadFactory-6-thread-5:SolrException@159] - {} - Collection:
> my_collection operation: delete failed:org.apache.solr.common.SolrException:
> Could not fully remove collection: my_collection
> at
> org.apache.solr.cloud.DeleteCollectionCmd.call(DeleteCollectionCmd.java:106)
> at
> org.apache.solr.cloud.OverseerCollectionMessageHandler.processMessage(OverseerCollectionMessageHandler.java:224)
> at
> org.apache.solr.cloud.OverseerTaskProcessor$Runner.run(OverseerTaskProcessor.java:463)
> {noformat}
> After that all operations with SolrCloud that involve reading cluster state
> fail with
> {noformat}
> org.apache.solr.common.SolrException: Error loading config name for
> collection my_collection
> at
> org.apache.solr.common.cloud.ZkStateReader.readConfigName(ZkStateReader.java:198)
> at
> org.apache.solr.handler.admin.ClusterStatus.getClusterStatus(ClusterStatus.java:141)
> ...
> Caused by: org.apache.zookeeper.KeeperException$NoNodeException:
> KeeperErrorCode = NoNode for /collections/my_collection
> ...
> {noformat}
> See full
> [stacktraces|https://gist.github.com/serba/9b7932f005f34f6cd9a511e226c6f0c6]
> As a result SolrCloud becomes completely broken. We are seeing this with
> 6.5.1 but I think we’ve seen that with older versions too.
> From looking into the code it looks like it is a combination of two factors:
> * Forcefully removing collection's znode in finally block in
> [DeleteCollectionCmd|https://github.com/apache/lucene-solr/blob/releases/lucene-solr/6.5.1/solr/core/src/java/org/apache/solr/cloud/DeleteCollectionCmd.java#L115]
> that was introduced in SOLR-5135. Note that this causes cached cluster state
> to be not in sync with the state in Zk, i.e.
> {{zkStateReader.getClusterState()}} still has collection in it (see the code
> [here|https://github.com/apache/lucene-solr/blob/releases/lucene-solr/6.5.1/solr/core/src/java/org/apache/solr/cloud/DeleteCollectionCmd.java#L98])
> whereas {{/collections/<collection_id>}} znode in Zk is already removed.
> * Reading cluster state operation not only returns cached version, but it is
> also reading collection's config name from {{/collections/<collection_id>}}
> znode, but this znode was forcefully removed. The code to read config name
> for every collection directly from Zk was introduced in SOLR-7636. Isn't
> there any performance implications of reading N znodes (1 per collection) on
> every {{getClusterStatus}} call?
> I'm not sure what the proper fix should be
> * Should we just catch {{KeeperException$NoNodeException}} in
> {{getClusterStatus}} and treat such collection as removed? That looks easiest
> / less invasive fix.
> * Should we stop reading config name from collection znode and get it from
> cache somehow?
> * Should we not try to delete collection's data from Zk if delete operation
> failed?
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