** 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
[email protected]
http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
