When you say "CPU" does that mean "logical CPU core"? Or is this actually referring to physical CPU cores?
E.g. On my laptop with 4 physical cores + HyperThreading, should I set +S to +S 4:4 You hint that it doesn't matter, but I just wanted to trick you into explicitly saying something. --- Jeremiah Peschka - Founder, Brent Ozar Unlimited MCITP: SQL Server 2008, MVP Cloudera Certified Developer for Apache Hadoop On Tue, Aug 13, 2013 at 5:38 PM, Matthew Von-Maszewski <matth...@basho.com>wrote: > ** The following is copied from Basho's leveldb wiki page: > > https://github.com/basho/leveldb/wiki/Riak-tuning-1 > > > > Summary: > > leveldb has a higher read and write throughput in Riak if the Erlang > scheduler count is limited to half the number of CPU cores. Tests have > demonstrated improvements of 15% to 80% greater throughput. > > The scheduler limit is set in the vm.args file: > > +S x:x > > where "x" is the number of schedulers Erlang may use. Erlang's default > value of "x" is the total number of CPUs in the system. For Riak > installations using leveldb, the recommendation is to set "x" to half the > number of CPUs. Virtual environments are not yet tested. > > Example: for 24 CPU system > > +S 12:12 > > Discussion: > > We have tested a limited number of CPU configurations and customer loads. > In all cases, there is a performance increase when the +S option is added > to the vm.args file to reduce the number of Erlang schedulers. The working > hypothesis is that the Erlang schedulers perform enough "busy wait" work > that they always create context switch away from leveldb when leveldb is > actually the only system task with real work. > > The tests included 8 CPU (no hyper threading, physical cores only) and 24 > CPU (12 physical cores with hyper threading) systems. All were 64bit Intel > platforms. Generalized findings: > > • servers running higher number of vnodes (64) had larger > performance gains than those with fewer (8) > • servers running SSD arrays had larger performance gains than > those running SATA arrays > • Get and Write operations showed performance gains, 2i query > operations (leveldb iterators) were unchanged > • Not recommended for servers with less than 8 CPUs (go no lower > than +S 4:4) > > Performance improvements were as high as 80% over extended, heavily loaded > intervals on servers with SSD arrays and 64 vnodes. No test resulted in > worse performance due to the addition of +S x:x. > > The +S x:x configuration change does not have to be implemented > simultaneously to an entire Riak cluster. The change may be applied to a > single server for verification. Steps: update the vm.args file, then > restart the Riak node. Erlang command line changes to schedules were > ineffective. > > This configuration change has been running in at least one large, > multi-datacenter production environment for several months. > > > _______________________________________________ > riak-users mailing list > riak-users@lists.basho.com > http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com >
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