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From "Dickson, Matt MR" <>
Subject RE: How to speed up table compaction [SEC=UNOFFICIAL]
Date Tue, 06 May 2014 23:10:57 GMT

To sumamrise the outcome of this.

In the past 24hours the compactions have reduced from 58K to 6K primarily due to increasing
the tserver.compaction.major.concurrent.max to 18 (requires all tservers to be restarted).
 The default is 3 so initially I had only pushed it up to 10 to leave head room for other
processes but had not seen major increases in performance.

Due to disk space constraints I left the tserver.file.compress.type as gz.  The other settings
altered were,, tserver.memory.maps.max and
tserver.walog.max.size.  We increased all these to maximise memory usage but aren't confident
these had a big impact on the compaction progress.

For completeness, the reason I had to run a table compact was because there were tablets on
the table that were receiving no new data and therefore the ageoff filter was never being
applied due to no compactions being triggered on these tablets. I posted a question in the
user group "Identify tablets with no new data loaded" on 30/4/14 trying to find a clean way
to identify these tablets via timestamps in the metadata table.  The goal was to only compact
the necessary ranges rather than this approach which is quite heavy handed.  I'm still keen
to persue an idea related to inspecting the files in hdfs to get the time of the last compact,
but that's a topic for another post.  Any suggestions are welcome.

Thanks again to everyone for all the feedback.

From: David Medinets []
Sent: Wednesday, 7 May 2014 01:52
To: accumulo-user
Subject: Re: How to speed up table compaction [SEC=UNOFFICIAL]

Can that property be changed on the fly? And Snappy needs to . On Tue, May 6, 2014 at 12:43
AM, Josh Elser <<>> wrote:

Depending on the CPU/IO ratio for your system, switching to a different compression codec
might help. Snappy tends to be a bit quicker writing out data as opposed to gzip at the cost
of being larger on disk. The increase in final size on disk might be prohibitive depending
on your requirements though.

I forget the table property off hand, but, if you haven't changed this already, it will be
the property with a defauly value of 'gz' :)

On May 5, 2014 6:43 PM, "Dickson, Matt MR" <<>>


I'm trying to compact a table and have had a queue of 60,000 compactions with only 800 running
at a time.  This has now been running for 4 days and only decreased the queue by 8,000.

I've increased tserver.compaction.major.concurrent.max=12 and stopped all ingest but not seen
a change in progress.  Are there other accumulo settings I can alter to improve this?  I also
saw should this be increased?

Thanks in advance,

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