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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7872) ensure compacted obsolete sstables are not open on node restart and nodetool refresh, even on sstable reference miscounting or deletion tasks are failed.
Date Sun, 05 Oct 2014 08:26:33 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14159470#comment-14159470
] 

Pavel Yaskevich commented on CASSANDRA-7872:
--------------------------------------------

bq. Having it deleted on next CMS gc (i.e. at some not exactly predictable point in near future)
is IMO better than having them never deleted. 

If you can back quoted statement up with any document (JMM or other) that explicitly guarantees
cleanup behavior you described (being, it's guaranteed to happen on CMS or minor collection
for phantom references) I would be fine adding #3, meanwhile there is no real point of arguing
about adding code that relies on the implementation detail and may never actually trigger.

> ensure compacted obsolete sstables are not open on node restart and nodetool refresh,
even on sstable reference miscounting or deletion tasks are failed.
> ---------------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-7872
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7872
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Oleg Anastasyev
>            Assignee: Oleg Anastasyev
>             Fix For: 2.0.11
>
>         Attachments: EnsureNoObsoleteSSTables-7872-v2.0.txt
>
>
> Since CASSANDRA-4436 compacted sstables are no more marked with COMPACTED_MARKER file.
Instead after they are compacted, DataTracker calls SSTableReader.markObsolete(), but the
actual deletion is happening later on SSTableReader.releaseReference().
> This reference counting is very fragile, it is very easy to introduce a hard-to-catch
and rare bug, so this reference count never reaches 0 ( like CASSANDRA-6503 for example )
> This means, that very rarely obsolete sstable files are not removed from disk (but are
not used anymore by cassandra to read data).
> If more than gc grace time has passed since sstable file was not removed from disk and
operator issues either nodetool refresh or just reboots a node, these obsolete files are being
discovered and open for read by a node. So deleted data is resurrected, being quickly spread
by RR to whole cluster.
> Because consequences are very serious (even a single not removed obsolete sstable file
could render your data useless) this patch makes sure no obsolete sstable file can be open
for read by:
> 1. Removing sstables on CFS init analyzing sstable generations (sstable is removed, if
there are another sstable, listing this as ancestor)
> 2. Reimplementing COMPACTED_MARKER file for sstable. This marker is created as soon as
markObsolete is called. This is neccessary b/c generation info can be lost (when sstables
compact to none)
> 3. To remove sstables sooner then restart - reimplemented the good old GC phantom reference
queue as well. 



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