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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Reopened] (CASSANDRA-8312) Use live sstables in snapshot repair if possible
Date Tue, 09 Dec 2014 12:42:13 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-8312?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Benedict reopened CASSANDRA-8312:
---------------------------------

It looks to me like this doesn't tidy up after itself properly, at least on trunk. It opens
an sstable from the snapshot if necessary, references it, and then releases only the reference
it acquired - not the extra reference that would permit its BF etc. to be reclaimed. So this
will likely leak significant amounts of memory.

> Use live sstables in snapshot repair if possible
> ------------------------------------------------
>
>                 Key: CASSANDRA-8312
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8312
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jimmy Mårdell
>            Assignee: Jimmy Mårdell
>            Priority: Minor
>             Fix For: 2.0.12, 3.0, 2.1.3
>
>         Attachments: cassandra-2.0-8312-1.txt
>
>
> Snapshot repair can be very much slower than parallel repairs because of the overhead
of opening the SSTables in the snapshot. This is particular true when using LCS, as you typically
have many smaller SSTables then.
> I compared parallel and sequential repair on a small range on one of our clusters (2*3
replicas). With parallel repair, this took 22 seconds. With sequential repair (default in
2.0), the same range took 330 seconds! This is an overhead of 330-22*6 = 198 seconds, just
opening SSTables (there were 1000+ sstables). Also, opening 1000 sstables for many smaller
rangers surely causes lots of memory churning.
> The idea would be to list the sstables in the snapshot, but use the corresponding sstables
in the live set if it's still available. For almost all sstables, the original one should
still exist.



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