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https://issues.apache.org/jira/browse/SOLR-13975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16993463#comment-16993463
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ASF subversion and git services commented on SOLR-13975:
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Commit 783a40a93cb1a3ea6421da99649570aeaeb5fefd in lucene-solr's branch
refs/heads/branch_8x from Andrzej Bialecki
[ https://gitbox.apache.org/repos/asf?p=lucene-solr.git;h=783a40a ]
SOLR-13975, SOLR-13896: ConcurrentUpdateSolrClient connection stall prevention.
> ConcurrentUpdateSolrClient connection stall prevention
> ------------------------------------------------------
>
> Key: SOLR-13975
> URL: https://issues.apache.org/jira/browse/SOLR-13975
> Project: Solr
> Issue Type: Bug
> Security Level: Public(Default Security Level. Issues are Public)
> Affects Versions: 8.3, 8.4
> Reporter: Andrzej Bialecki
> Assignee: Andrzej Bialecki
> Priority: Major
> Fix For: 8.4
>
> Attachments: SOLR-13975.patch, SOLR-13975.patch
>
>
> When a Solr process, which hosts replicas of a collection, is suspended -
> that is, the OS process is suspended using eg. {{kill -STOP <pid>}} - a long
> stall may occur in CUSC until a socket timeout is reached.
> During this stall updates from the leader are not forwarded to any replica,
> even though other replicas are still active and can receive updates. If the
> sender uses CUSC (eg. via {{CloudSolrClient}}) then it becomes stalled
> because the leader stops processing updates, too.
> This situation is caused by several issues:
> * when a process is suspended its sockets remain open - so there is no
> immediate disconnect as if the process died, but the process becomes
> unresponsive. Eventually, a socket timeout will be reached
> (distribUpdateSoTimeout) - but in the default version of {{solr.xml}} this is
> set to 10 min. During this time all indexing to that shard will be stuck.
> * there are several infinite {{for}} loops in CUSC (eg. in
> {{blockUntilFinished}}, {{waitForEmptyQueue}} and even in {{request}}), which
> rely either on the relatively quick success of the call or an exception to be
> thrown. However, in this situation neither happens quickly - the call is
> stuck waiting for the remote end until soTimeout expires.
> This issue proposes to add a stall prevention logic, which would break these
> infinite loops long before the socket timeout occurs based on the progress of
> the queue processing.
> This is a follow-up to SOLR-13896.
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