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From Germán Kondolf <>
Subject Re: Parallel Compaction
Date Fri, 17 Dec 2010 13:01:07 GMT
Thanks Jonathan for the feedback.

By flush/schema migration you mean the SSTables replace lock? I've put
that lock just to be sure, if it's fine by you I'll remove it.
I'll clean up the code according to the code-style article, add the
parameter to the configuration using a default of "1" and I'll send it

Why do you think is only worth it on SSDs?
How do I get to commit this patch?

On Fri, Dec 17, 2010 at 2:41 AM, Jonathan Ellis <> wrote:
> Hi Germán,
> Thanks for taking a stab at this!
> I don't actually think there are going to be any tricky race conditions with
> flush or schema migration; flush has been parallel for a long time itself,
> and we already have the lock in CompactionManager for schema migration.
> To clean this up for submission you'd want to follow the style guide at
>, r/m the commented-out sections,
> and add a configuration parameter for how many compactions to allow
> simultaneously (IMO it mainly only makes sense to have > 1 when you are
> running on SSDs, and there's no good way for us to auto-detect that).
> On Thu, Dec 16, 2010 at 6:04 PM, Germán Kondolf <>wrote:
>> Hi everybody,
>> I've just finished the first implementation of a Parallel Compaction
>> Patch for the trunk version, tomorrow I'll test it with high volumen
>> of data to see if it works as I expected, but before I wan't to
>> validate with you the approach.
>> I know it's kinda naif, but, maybe it works as starting point for a
>> future production implementation or at least allow to make
>> configurable the compaction strategy.
>> First of all, I don't know in depth the C* code, so maybe I took a few
>> shortcuts and that's why I need a second look from an expert...
>> I've modified the doCompaction method of CompactionManager, added a
>> few static classes (I'm working to remove them, so V2 is coming), and
>> simply splitted the sstables to compact in a balanced order and fire
>> each group compaction in parallel.
>> The revision I've based the patch is: 1050234
>> The files are attached, the patch and the
>> Thanks in advance, I'll appreciate the feedback.
>> --
>> //GK
>> // sites
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of Riptano, the source for professional Cassandra support

// sites

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