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From Ken Hancock <ken.hanc...@schange.com>
Subject Re: Flush writer all time blocked
Date Thu, 29 Aug 2013 18:40:57 GMT
# the number of full memtables to allow pending flush, that is,
# waiting for a writer thread.  At a minimum, this should be set to
# the maximum number of secondary indexes created on a single CF.
memtable_flush_queue_size: 4

There was an interesting thread a while back:

http://mail-archives.apache.org/mod_mbox/cassandra-user/201307.mbox/%3C17C39FE466076C46B6E83F129C7B19CE2E7EC86A@HKXPRD0310MB352.apcprd03.prod.outlook.com%3E


On Thu, Aug 29, 2013 at 2:23 PM, S C <asf11@outlook.com> wrote:
> Ken,
>
> What queue size are you referring to?
>
> Thanks,
> SC
>
>
>> From: ken.hancock@schange.com
>> Date: Thu, 29 Aug 2013 14:21:04 -0400
>> Subject: Re: Flush writer all time blocked
>> To: user@cassandra.apache.org
>>
>> On Thu, Aug 29, 2013 at 1:57 PM, Robert Coli <rcoli@eventbrite.com> wrote:
>> > On Thu, Aug 29, 2013 at 10:49 AM, S C <asf11@outlook.com> wrote:
>> >> I see a high count "All time blocked" for Flush Writer on nodetool
>> >> tpstats.
>> >>
>> >> Is it how many blocked ever since the server was online? Can somebody
>> >> explain me what it is? I really appreciate it.
>> >
>> >
>> > Yes.
>> >
>> > Flush Writer thread pool is the thread pool responsible for the part of
>> > memtable flush that actually writes to disk.
>> > If you see it with a non-zero blocked number, you have at some time
>> > written to memory significantly faster than you
>> > could flush to disk.
>>
>> I don't think this is strictly true? There's also the periodic flush
>> that can cause a storm of flushes if you have multiple column
>> families. I sent out a query to the list last week on this topic but
>> didn't get any responses -- I'm very interested in this topic as I've
>> had to set my queue size fairly large to avoid this issue.
>>
>> Ken



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