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https://issues.apache.org/jira/browse/SOLR-9941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15824621#comment-15824621
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ASF subversion and git services commented on SOLR-9941:
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Commit 38af094d175daebe4093782cc06e964cfc2dd14b in lucene-solr's branch
refs/heads/master from [~ichattopadhyaya]
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=38af094 ]
SOLR-9941: Moving changelog entry from 7.0.0 to 6.5.0
> log replay redundently (pre-)applies DBQs as if they were out of order
> ----------------------------------------------------------------------
>
> Key: SOLR-9941
> URL: https://issues.apache.org/jira/browse/SOLR-9941
> Project: Solr
> Issue Type: Improvement
> Security Level: Public(Default Security Level. Issues are Public)
> Reporter: Hoss Man
> Assignee: Ishan Chattopadhyaya
> Attachments: SOLR-9941.hoss-test-experiment.patch, SOLR-9941.patch,
> SOLR-9941.patch, SOLR-9941.patch, SOLR-9941.patch, SOLR-9941.patch
>
>
> There's kind of an odd situation that arises when a Solr node starts up
> (after a crash) and tries to recover from it's tlog that causes deletes to be
> redundantly & excessively applied -- at a minimum it causes confusing really
> log messages....
> * {{UpdateLog.init(...)}} creates {{TransactionLog}} instances for the most
> recent log files found (based on numRecordsToKeep) and then builds a
> {{RecentUpdates}} instance from them
> * Delete entries from the {{RecentUpdates}} are used to populate 2 lists:
> ** {{deleteByQueries}}
> ** {{oldDeletes}} (for deleteById).
> * Then when {{UpdateLog.recoverFromLog}} is called a {{LogReplayer}} is used
> to replay any (uncommited) {{TransactionLog}} enteries
> ** during replay {{UpdateLog}} delegates to the UpdateRequestProcessorChain
> to for the various adds/deletes, etc...
> ** when an add makes it to {{RunUpdateProcessor}} it delegates to
> {{DirectUpdateHandler2}}, which (independent of the fact that we're in log
> replay) calls {{UpdateLog.getDBQNewer}} for every add, looking for any
> "Reordered" deletes that have a version greater then the add
> *** if it finds _any_ DBQs "newer" then the document being added, it does a
> low level {{IndexWriter.updateDocument}} and then immediately executes _all_
> the newer DBQs ... _once per add_
> ** these deletes are *also* still executed as part of the normal tlog replay,
> because they are in the tlog.
> Which means if you are recovering from a tlog with 90 addDocs, followed by 5
> DBQs, then *each* of those 5 DBQs will each be executed 91 times -- and for
> 90 of those executions, a DUH2 INFO log messages will say {{"Reordered DBQs
> detected. ..."}} even tough the only reason they are out of order is because
> Solr is deliberately applying them out of order.
> * At a minimum we should improve the log messages
> * Ideally we should stop (pre-emptively) applying these deletes during tlog
> replay.
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