Michael has a good point about the system tables - particularly hints and batching (though neither should be a real tax unless you have bigger issues).
If you have a monitoring system, add in the flush counters for these and other higher traffic tables and see if there is a correlation at the four hour mark with monitoring output of the GC statistics. On Tue, Dec 10, 2013 at 9:58 AM, Laing, Michael <michael.la...@nytimes.com>wrote: > 2.0.3: system tables have a 1 hour memtable_flush_period which I have > observed to trigger compaction on the 4 hour mark. Going by memory tho... > -ml > > > On Tue, Dec 10, 2013 at 10:31 AM, Andre Sprenger < > andre.spren...@getanet.de> wrote: > >> As far as I know there is nothing hard coded in Cassandra that kicks in >> every 4 hours. Turn on GC logging, maybe dump the output of jstats to a >> file and correlate this data with the Cassandra logs. Cassandra logs are >> pretty good in telling you what is going on. >> >> >> 2013/12/10 Joel Samuelsson <samuelsson.j...@gmail.com> >> >>> Hello, >>> >>> We've been having a lot of problems with extremely long GC (and still >>> do) which I've asked about several times on this list (I can find links to >>> those discussions if anyone is interested). >>> We noticed a pattern that the GC pauses may be related to something >>> happening every 4 hours. Is there anything specific happening within >>> Cassandra with a 4 hour interval? >>> >>> Any help is much appreciated, >>> Joel Samuelsson >>> >> >> > -- ----------------- Nate McCall Austin, TX @zznate Co-Founder & Sr. Technical Consultant Apache Cassandra Consulting http://www.thelastpickle.com
