Increase memtable_flush_writers. In cassandra.yaml, it was recommended to increase this setting when SSDs used for storing data.
On Fri, Jul 24, 2015 at 1:55 PM, Soerian Lieve <sli...@liveramp.com> wrote: > I was on CFQ so I changed it to noop. The problem still persisted however. > Do you have any other ideas? > > On Thu, Jul 23, 2015 at 5:00 PM, Jeff Ferland <j...@tubularlabs.com> wrote: > >> Imbalanced disk use is ok in itself. It’s only saturated throughput >> that’s harmful. RAID 0 does give more consistent throughput and balancing, >> but that’s another story. >> >> As for your situation with SSD drive, you can probably tweak this by >> changing the scheduler is set to noop, or read up on >> https://www.kernel.org/doc/Documentation/block/deadline-iosched.txt for >> the deadline scheduler (lower writes_starved value). If you’re one CFQ, >> definitely ditch it. >> >> -Jeff >> >> On Jul 23, 2015, at 4:17 PM, Soerian Lieve <sli...@liveramp.com> wrote: >> >> I set up RAID0 after experiencing highly imbalanced disk usage with a >> JBOD setup so my transaction logs are indeed on the same media as the >> sstables. >> Is there any alternative to setting up RAID0 that doesn't have this issue? >> >> On Thu, Jul 23, 2015 at 4:03 PM, Jeff Ferland <j...@tubularlabs.com> >> wrote: >> >>> My immediate guess: your transaction logs are on the same media as your >>> sstables and your OS prioritizes read requests. >>> >>> -Jeff >>> >>> > On Jul 23, 2015, at 2:51 PM, Soerian Lieve <sli...@liveramp.com> >>> wrote: >>> > >>> > Hi, >>> > >>> > I am currently performing benchmarks on Cassandra. Independently from >>> each other I am seeing ~100k writes/sec and ~50k reads/sec. When I read and >>> write at the same time, writing drops down to ~1000 writes/sec and reading >>> stays roughly the same. >>> > >>> > The heap used is the same as when only reading, as is the disk >>> utilization. Replication factor is 3, consistency level on both reads and >>> writes is ONE. Using Cassandra 2.1.6. All cassandra.yaml settings set up >>> according to the Datastax guide. All nodes are running on SSDs. >>> > >>> > Any ideas what could cause this? >>> > >>> > Thanks, >>> > Soerian >>> >>> >> >> >
