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From aaron morton <aa...@thelastpickle.com>
Subject Re: Consurrent compactors
Date Wed, 01 Feb 2012 19:51:18 GMT
(Assuming 1.0* release)
From the comments in cassandra.yaml

# Number of simultaneous compactions to allow, NOT including
# validation "compactions" for anti-entropy repair.  Simultaneous
# compactions can help preserve read performance in a mixed read/write
# workload, by mitigating the tendency of small sstables to accumulate
# during a single long running compactions. The default is usually
# fine and if you experience problems with compaction running too
# slowly or too fast, you should look at
# compaction_throughput_mb_per_sec first.
#
# This setting has no effect on LeveledCompactionStrategy.
#
# concurrent_compactors defaults to the number of cores.
# Uncomment to make compaction mono-threaded, the pre-0.8 default.
#concurrent_compactors: 1

If you set it to 1 then only 1 compaction should run at a time, excluding validation. 

How often do you run a cleanup compaction ? They are only necessary when you perform a token
move.

Cheers

-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 1/02/2012, at 9:48 PM, Viktor Jevdokimov wrote:

> Hi,
>  
> When concurrent compactors are set to more then 1, it’s rare when more than 1 compaction
is running in parallel.
>  
> Didn’t checked the source code, but it looks like when next compaction task (any of
minor, major, or cleanup) is for the same CF, it will not start in parallel and next tasks
are not checked.
>  
> Will it be possible to check all tasks, not only the next one, to find which of them
can be started?
>  
> This is actual especially when nightly cleanup is running, a lot of cleanup tasks are
pending, regular minor compactions are waiting until all cleanup compactions are finished.
>  
>  
>  
> Best regards/ Pagarbiai
>  
> Viktor Jevdokimov
> Senior Developer
>  
> Email:  Viktor.Jevdokimov@adform.com
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