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From "Varun Sharma (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-8599) HLogs in ZK are not cleaned up when replication lag is minimal
Date Thu, 23 May 2013 18:15:21 GMT
Varun Sharma created HBASE-8599:
-----------------------------------

             Summary: HLogs in ZK are not cleaned up when replication lag is minimal
                 Key: HBASE-8599
                 URL: https://issues.apache.org/jira/browse/HBASE-8599
             Project: HBase
          Issue Type: Improvement
          Components: Replication
    Affects Versions: 0.94.7
            Reporter: Varun Sharma


On a cluster with very low replication lag (as measured by ageOfLastShippedOp on source),
we found HLogs accumulating and not being cleaned up as new WAL(s) are rolled.

Each time, we call logPositionAndCleanOldLogs() to clean older logs whenever the current WAL
is not being written to any more - as suggested by currentWALBeingWrittenTo being false. However,
when lags are small, we may hit the following block first and continue onto the next WAL without
clearing the old WAL(s)...

ReplicationSource::run() {
    if (readAllEntriesToReplicateOrNextFile(currentWALisBeingWrittenTo = false)) {
        // If we are here, then we advance to the next WAL without any cleaning
        // and close existing WAL
        continue;
    }
    // Ship some edits and call logPositionAndCleanOldLogs
}

If we hit readAllEntriesToReplicateOrNextFile(false) only once - then older logs are not cleaned
out and persist in the zookeeper node since we simply call "continue" and skip the subsequent
logPositionAndCleanOldLogs call - if its called more than once, we do end up clearing the
old logs.






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