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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (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 Sat, 04 Oct 2014 01:04:40 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14158833#comment-14158833
] 

Pavel Yaskevich edited comment on CASSANDRA-7872 at 10/4/14 1:04 AM:
---------------------------------------------------------------------

I can agree with #1 and #2 from the description (with minor code refactoring in v2.0 patch
e.g. curly brackets should be on separate lines, no need to use Collection if creating a Set,
if shouldn't have spaces before and after conditions) but I would rather not include #3 as
phantom references are tricky business and only cleaned by by FullGC. 


was (Author: xedin):
I can agree with #1 and #2 from the description (with minor code stuff refactoring in v2.0
patch) but I would rather not include #3 as phantom references are tricky business and only
cleaned by by FullGC. 

> 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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