Andrzej Bialecki created SOLR-13975:
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Summary: 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)
Reporter: Andrzej Bialecki
Assignee: Andrzej Bialecki
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.
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