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From Thorsten von Eicken <...@rightscale.com>
Subject Re: how to increase compaction rate?
Date Tue, 13 Mar 2012 17:27:28 GMT
On 3/12/2012 6:52 AM, Brandon Williams wrote:
> On Mon, Mar 12, 2012 at 4:44 AM, aaron morton <aaron@thelastpickle.com> wrote:
>> I don't understand why I
>> don't get multiple concurrent compactions running, that's what would
>> make the biggest performance difference.
>>
>> concurrent_compactors
>> Controls how many concurrent compactions to run, by default it's the number
>> of cores on the machine.
I'm on a quad-core machine so not setting concurrent_compactors should
not be a limiting factor...
> With leveled compaction, I don't think you get any concurrency because
> it has to compact an entire level, and it can't proceed to the next
> level without completing the one before it.
>
> In short, if you want maximum throughput, stick with size tiered.
I switched the CFs to tiered compaction and I still get no concurrency
for the same CF. I now have two compactions running concurrently but
always for different CFs. I've briefly seen a third for one of the small
CFs, so it's willing to run more than two concurrently. Looks like I
have to wait for a few days for all the compactions to complete. Talk
about compaction hell!

>
> -Brandon
>

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