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From "Alex Markham (JIRA)" <>
Subject [jira] [Created] (COUCHDB-1505) Error on cancelling replication - possbily related to hanging replications
Date Wed, 27 Jun 2012 09:31:42 GMT
Alex Markham created COUCHDB-1505:

             Summary: Error on cancelling replication - possbily related to hanging replications
                 Key: COUCHDB-1505
             Project: CouchDB
          Issue Type: Bug
          Components: Replication
    Affects Versions: 1.2
         Environment: CentOS 5.6 x64. WAN replication (between datacentres). Cronjob controlled
replication curls every 5 mins. Using pull replication with a filter.
            Reporter: Alex Markham
         Attachments: couchjs.txt, replicationcancelerror1.log

We run a cronjob to cancel replication, and then start it again every 5 minutes. Occasionally
when cancelling replication jobs, a stack trace appears in the couchdb log (attached)

Other observations : perhaps unrelated, but over time we slowly start to gather "zombie" couchjs
processes. After a month or so (different for each server) we start to get up to near our
os_process_limit of 200 and we restart couchdb. "zombie" is speculation here, but there seems
to be no need for the hundred+ couchjs processes when just replicating 10 databases and occasional
indexing, after restart it drops right back down. The started time of those processes are
also weeks old. This may be normal, not sure.

Why do we cancel replication and restart it? We found that if we don't do this then WAN replications
can hang, where curling /_replicate would say that the continuous replication is already running,
but that the replications were not updating, and the document counts in the databases would
diverge. Immediately after re-enabling the "cancel":true /_replicate beforehand, these stack
traces re-appeared and the replication caught up.

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