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https://issues.apache.org/jira/browse/SOLR-7869?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14680727#comment-14680727
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Shalin Shekhar Mangar commented on SOLR-7869:
---------------------------------------------
bq. In that case, I would suggest an explicit catch block there for
BadVersionException, and log something milder than error? The current
KeeperException catch block always logs an error.
+1
bq. Work items get removed from the queue before the corresponding change is
actually written out to the cluster state. You can see in the original design
that there's this neat peek->poll dance in the Overseer loop that attempts to
enforce guaranteed state updates by not discarding the work item until after
the state is written out. But the batching implementation gets rid of this
guarantee, and that's why I perceive we're now in a state where the overseer
updates and external updates can even be in conflict with each other.
No, items are never removed until they're flushed to ZK. This invariant is
maintained everywhere. If you find that I have missed a case then please do let
me know. When operating on the work queue, batching is completely disabled
because we have no fallback in case we fail. When operating on the main queue
-- we add operation to work queue when onEnqueue event is called and we remove
item from work queue once onWrite event is called. This ensures that we never
lose an operation.
bq. But I really do think we're batching in the wrong place. I think batching
actually needs to happen in Overseer, because it has to be tied to discarding
work items.
That used to be the case. I refactored Overseer extensively in 5.0 in SOLR-6554
bq. (Now, all that said, that work may be more effort than it's worth, and
maybe we should just focus on not having to use the queue to make cluster state
updates in the format v2 world.)
Yeah, I think a more worthwhile improvement would be SOLR-6760
> Overseer does not handle BadVersionException correctly
> ------------------------------------------------------
>
> Key: SOLR-7869
> URL: https://issues.apache.org/jira/browse/SOLR-7869
> Project: Solr
> Issue Type: Bug
> Components: SolrCloud
> Affects Versions: 5.2.1
> Reporter: Shalin Shekhar Mangar
> Assignee: Shalin Shekhar Mangar
> Labels: difficulty-medium, impact-low
> Fix For: Trunk, 5.4
>
> Attachments: SOLR-7869.patch, SOLR-7869.patch
>
>
> If the /clusterstate.json is modified externally then the Overseer can go
> into an infinite loop upon a BadVersionException alternately trying to
> execute main queue and then the work queue:
> {code}
> ERROR - 2015-08-04 18:49:56.224; [ ]
> org.apache.solr.cloud.Overseer$ClusterStateUpdater; Exception in Overseer
> work queue loop
> org.apache.zookeeper.KeeperException$BadVersionException: KeeperErrorCode =
> BadVersion for /clusterstate.json
> at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:115)
> at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
> at org.apache.zookeeper.ZooKeeper.setData(ZooKeeper.java:1270)
> at
> org.apache.solr.common.cloud.SolrZkClient$8.execute(SolrZkClient.java:362)
> at
> org.apache.solr.common.cloud.SolrZkClient$8.execute(SolrZkClient.java:359)
> at
> org.apache.solr.common.cloud.ZkCmdExecutor.retryOperation(ZkCmdExecutor.java:61)
> at
> org.apache.solr.common.cloud.SolrZkClient.setData(SolrZkClient.java:359)
> at
> org.apache.solr.cloud.overseer.ZkStateWriter.writePendingUpdates(ZkStateWriter.java:180)
> at
> org.apache.solr.cloud.overseer.ZkStateWriter.enqueueUpdate(ZkStateWriter.java:67)
> at
> org.apache.solr.cloud.Overseer$ClusterStateUpdater.processQueueItem(Overseer.java:286)
> at
> org.apache.solr.cloud.Overseer$ClusterStateUpdater.run(Overseer.java:168)
> at java.lang.Thread.run(Thread.java:745)
> INFO - 2015-08-04 18:49:56.224; [ ]
> org.apache.solr.cloud.Overseer$ClusterStateUpdater; processMessage:
> queueSize: 1, message = {
> "operation":"state",
> "state":"down",
> "base_url":"http://127.0.1.1:7574/solr";,
> "core":"test_shard1_replica1",
> "roles":null,
> "node_name":"127.0.1.1:7574_solr",
> "shard":null,
> "collection":"test",
> "core_node_name":"core_node1"} current state version: 9
> INFO - 2015-08-04 18:49:56.224; [ ]
> org.apache.solr.cloud.overseer.ReplicaMutator; Update state numShards=null
> message={
> "operation":"state",
> "state":"down",
> "base_url":"http://127.0.1.1:7574/solr";,
> "core":"test_shard1_replica1",
> "roles":null,
> "node_name":"127.0.1.1:7574_solr",
> "shard":null,
> "collection":"test",
> "core_node_name":"core_node1"}
> INFO - 2015-08-04 18:49:56.224; [ ]
> org.apache.solr.cloud.overseer.ReplicaMutator; shard=shard1 is already
> registered
> ERROR - 2015-08-04 18:49:56.225; [ ]
> org.apache.solr.cloud.Overseer$ClusterStateUpdater; Exception in Overseer
> main queue loop
> org.apache.zookeeper.KeeperException$BadVersionException: KeeperErrorCode =
> BadVersion for /clusterstate.json
> at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:115)
> at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:51)
> at org.apache.zookeeper.ZooKeeper.setData(ZooKeeper.java:1270)
> at
> org.apache.solr.common.cloud.SolrZkClient$8.execute(SolrZkClient.java:362)
> at
> org.apache.solr.common.cloud.SolrZkClient$8.execute(SolrZkClient.java:359)
> at
> org.apache.solr.common.cloud.ZkCmdExecutor.retryOperation(ZkCmdExecutor.java:61)
> at
> org.apache.solr.common.cloud.SolrZkClient.setData(SolrZkClient.java:359)
> at
> org.apache.solr.cloud.overseer.ZkStateWriter.writePendingUpdates(ZkStateWriter.java:180)
> at
> org.apache.solr.cloud.overseer.ZkStateWriter.enqueueUpdate(ZkStateWriter.java:67)
> at
> org.apache.solr.cloud.Overseer$ClusterStateUpdater.processQueueItem(Overseer.java:286)
> at
> org.apache.solr.cloud.Overseer$ClusterStateUpdater.run(Overseer.java:213)
> at java.lang.Thread.run(Thread.java:745)
> INFO - 2015-08-04 18:49:56.225; [ ]
> org.apache.solr.common.cloud.ZkStateReader; Updating data for gettingstarted
> to ver 8
> {code}
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