# 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/%3c17c39fe466076c46b6e83f129c7b19ce2e7ec...@hkxprd0310mb352.apcprd03.prod.outlook.com%3E On Thu, Aug 29, 2013 at 2:23 PM, S C <as...@outlook.com> wrote: > Ken, > > What queue size are you referring to? > > Thanks, > SC > > >> From: ken.hanc...@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 <rc...@eventbrite.com> wrote: >> > On Thu, Aug 29, 2013 at 10:49 AM, S C <as...@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 -- Ken Hancock | System Architect, Advanced Advertising SeaChange International 50 Nagog Park Acton, Massachusetts 01720 ken.hanc...@schange.com | www.schange.com | NASDAQ:SEAC Office: +1 (978) 889-3329 | ken.hanc...@schange.com | hancockks | hancockks This e-mail and any attachments may contain information which is SeaChange International confidential. The information enclosed is intended only for the addressees herein and may not be copied or forwarded without permission from SeaChange International.
