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From "Sharvanath Pathak (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-12778) Tombstones not being deleted when only_purge_repaired_tombstones is enabled
Date Tue, 18 Oct 2016 21:58:58 GMT


Sharvanath Pathak commented on CASSANDRA-12778:

There are multiple problems right now:
i) There can be cases when the tombstones can be looping in the cluster forever. For example,
even after a node purges a tombstones it can receive the same from read-repair and can rewrite
this old tombstones as unrepaired. We are seeing this happen even with read-repair disabled
and are debugging what else could cause this.

iI) Flush almost always triggers a compaction. This causes the data in these old SSTables
to not be repaired because the old SSTable which has been repaired is gone when it comes to
marking them repaired. Seems like this is a race and compaction should be disallowed (on some
fine granularity, e.g. keyspace) when repair is running.

iiI) The check for whether there is any overlapping data in other SSTables is very coarse
in granularity in that it looks at the minimumTimestamp of the non-compacting SSTables.

> Tombstones not being deleted when only_purge_repaired_tombstones is enabled
> ---------------------------------------------------------------------------
>                 Key: CASSANDRA-12778
>                 URL:
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Arvind Nithrakashyap
>            Assignee: Marcus Eriksson
>            Priority: Critical
> When we use only_purge_repaired_tombstones for compaction, we noticed that tombstones
are no longer being deleted.
> {noformat}compaction = {'class': 'org.apache.cassandra.db.compaction.LeveledCompactionStrategy',
'only_purge_repaired_tombstones': 'true'}{noformat}
> The root cause for this seems to be caused by the fact that repair itself issues a flush
which in turn leads to a new sstable being created (which is not in the repair set). It looks
like we do have some old data in this sstable because of this, only tombstones older than
that timestamp are getting deleted even though many more keys have been repaired. 
> Fundamentally it looks like flush and repair can race with each other and with leveled
compaction, the flush creates a new sstable at level 0 and removes the older sstable (the
one that is picked for repair). Since repair itself seems to issue multiple flushes, the level
0 sstable never gets repaired and hence tombstones never get deleted. 
> We have already included the fix for CASSANDRA-12703 while testing. 

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