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https://issues.apache.org/jira/browse/OAK-1167?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13819020#comment-13819020
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Marcel Reutegger commented on OAK-1167:
---------------------------------------
AFAICS this is caused by multiple threads concurrently calling
RevisionComparator.add() through different methods. There are mainly two
methods where add() is called for foreign revisions. The third, MongoNodeStore
constructor, is a bit of a special case because it only calls add() once on
startup.
- Revisions are added in MongoNodeStore.backgroundRead() by a dedicated
background thread
- Revisions are added in MongoNodeStore.publishRevision() by a committing
thread when a newer revision than the commit revision is seen.
The check whether to add the revision is implemented differently in the two
methods. backgroundRead() keeps a {{lastKnownRevision}} map, which contains the
most recent foreign revisions, while publishRevision() uses the head revision
to perform the check.
Either both methods must use the same algorithm to decide whether to add a
revision or RevisionComparator.add() must be more lenient when an attempt is
made to add a earlier revision.
> Background read may cause IllegalArgumentException
> --------------------------------------------------
>
> Key: OAK-1167
> URL: https://issues.apache.org/jira/browse/OAK-1167
> Project: Jackrabbit Oak
> Issue Type: Bug
> Components: core, mongomk
> Affects Versions: 0.10
> Reporter: Marcel Reutegger
> Assignee: Marcel Reutegger
>
> When running Oak with MongoMK and multiple cluster nodes the background read
> may sometimes cause an IllegalArgumentException like this:
> {noformat}
> 02:14:40.451 [MongoNodeStore background thread] WARN
> o.a.j.o.p.mongomk.MongoNodeStore - Background operation failed:
> java.lang.IllegalArgumentException: Can not add an earlier revision:
> r14246a7ee62-0-3 > r14246a7ea36-0-3; current cluster node is 2
> java.lang.IllegalArgumentException: Can not add an earlier revision:
> r14246a7ee62-0-3 > r14246a7ea36-0-3; current cluster node is 2
> at
> org.apache.jackrabbit.oak.plugins.mongomk.Revision$RevisionComparator.add(Revision.java:383)
> ~[oak-run-0.11-SNAPSHOT.jar:0.11-SNAPSHOT]
> at
> org.apache.jackrabbit.oak.plugins.mongomk.MongoNodeStore.backgroundRead(MongoNodeStore.java:1044)
> ~[oak-run-0.11-SNAPSHOT.jar:0.11-SNAPSHOT]
> at
> org.apache.jackrabbit.oak.plugins.mongomk.MongoNodeStore.runBackgroundOperations(MongoNodeStore.java:1000)
> ~[oak-run-0.11-SNAPSHOT.jar:0.11-SNAPSHOT]
> at
> org.apache.jackrabbit.oak.plugins.mongomk.MongoNodeStore$BackgroundOperation.run(MongoNodeStore.java:1221)
> [oak-run-0.11-SNAPSHOT.jar:0.11-SNAPSHOT]
> at java.lang.Thread.run(Thread.java:679) [na:1.6.0_24]
> {noformat}
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