cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
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 Mon, 06 Oct 2014 08:02:34 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7872?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14160086#comment-14160086
] 

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

I am not sure why are you trying to twist my words here, I didn't ever claim that FullGC never
happens with C* rather that we trying our best to reduce frequency of it to minimum. My concern
here is, as already stated, that #3 is intended as a safety net feature but we are trying
to rely on implementation detail which is never a good design, even tho it's currently this
way it doesn't mean it's here to say or works the same across the platforms and garbage collectors,
it's always better to address the problem instead of trying to fix it's sympthoms. That said,
if other people think it's a good idea I would comply.

> 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. 



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

Mime
View raw message