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From "Stu Hood (JIRA)" <>
Subject [jira] Updated: (CASSANDRA-2191) Multithread across compaction buckets
Date Fri, 18 Feb 2011 04:57:12 GMT


Stu Hood updated CASSANDRA-2191:

    Attachment: 0002-Use-the-compacting-set-of-sstables-to-schedule-multith.txt

Patch to add a "compacting" set to the SSTableTracker which is atomically modified to schedule
compactions. SSTables are removed from the compacting set in a finally block.

Also, converts the "compactionLock", which is only used by migrations (to completely stop
compactions), to a read-write lock. Running compactions acquire as readers, migrations acquire
as writer.

Implications: up to #num-procs compactions will run at once, possibly within the same bucket,
but likely in different buckets.

This patch goes hand in hand with CASSANDRA-2156, which ensures that despite our multithreading,
we don't trample other operations on the system.

> Multithread across compaction buckets
> -------------------------------------
>                 Key: CASSANDRA-2191
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Stu Hood
>            Priority: Critical
>              Labels: compaction
>             Fix For: 0.8
>         Attachments: 0001-Add-a-compacting-set-to-sstabletracker.txt, 0002-Use-the-compacting-set-of-sstables-to-schedule-multith.txt
> This ticket overlaps with CASSANDRA-1876 to a degree, but the approaches and reasoning
are different enough to open a separate issue.
> The problem with compactions currently is that they compact the set of sstables that
existed the moment the compaction started. This means that for longer running compactions
(even when running as fast as possible on the hardware), a very large number of new sstables
might be created in the meantime. We have observed this proliferation of sstables killing
performance during major/high-bucketed compactions.
> One approach would be to pause compactions in upper buckets (containing larger files)
when compactions in lower buckets become possible. While this would likely solve the problem
with read performance, it does not actually help us perform compaction any faster, which is
a reasonable requirement for other situations.
> Instead, we need to be able to perform any compactions that are currently required in
parallel, independent of what bucket they might be in.

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