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From Sheng Chen <>
Subject Re: Endless minor compactions after heavy inserts
Date Sat, 02 Apr 2011 01:45:39 GMT
Thank you very much.

The major compaction will merge everything into one big file., which would
be very large.
Is there any way to control the number or size of files created by major
Or, is there a recommended number or size of files for cassandra to handle?

Thanks. I see the trigger of my minor compaction is OperationsInMillions. It
is a number of operations in total, which I thought was in a second.


2011/4/1 aaron morton <>

> If you are doing some sort of bulk load you can disable minor compactions
> by setting the min_compaction_threshold and max_compaction_threshold to 0 .
> Then once your insert is complete run a major compaction via nodetool before
> turning the minor compaction back on.
> You can also reduce the compaction threads priority, see
> compaction_thread_priority in the yaml file.
> The memtable will be flushed when either the MB or ops throughput is
> triggered. If you are seeing a lot of memtables smaller than the MB
> threshold then the ops threshold is probably been triggered. Look for a log
> message at INFO level starting with "Enqueuing flush of Memtable" that will
> tell you how many bytes and ops the memtable had when it was flushed. Trying
> increasing the ops threshold and see what happens.
> You're change in the compaction threshold may not have an an effect because
> the compaction process was already running.
> AFAIK the best way to get the best out of your 10 disks will be to use a
> dedicated mirror for the commit log and a  stripe set for the data.
> Hope that helps.
> Aaron
> On 1 Apr 2011, at 14:52, Sheng Chen wrote:
> > I've got a single node of cassandra 0.7.4, and I used the java stress
> tool to insert about 100 million records.
> > The inserts took about 6 hours (45k inserts/sec) but the following minor
> compactions last for 2 days and the pending compaction jobs are still
> increasing.
> >
> > From jconsole I can read the MemtableThroughputInMB=1499,
> MemtableOperationsInMillions=7.0
> > But in my data directory, I got hundreds of 438MB data files, which
> should be the cause of the minor compactions.
> >
> > I tried to set compaction threshold by nodetool, but it didn't seem to
> take effects (no change in pending compaction tasks).
> > After restarting the node, my setting is lost.
> >
> > I want to distribute the read load in my disks (10 disks in xfs, LVM), so
> I don't want to do a major compaction.
> > So, what can I do to keep the sstable file in a reasonable size, or to
> make the minor compactions faster?
> >
> > Thank you in advance.
> > Sheng
> >

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