Are your commitlog and data on the same disk ? If yes, you should put commitlogs on a separate disk which don't have a lot of IO.
Others IO may have great impact impact on your commitlog writing and it may even block. An example of impact IO may have, even for Async writes: https://engineering.linkedin.com/blog/2016/02/eliminating-large-jvm-gc-pauses-caused-by-background-io-traffic 2016-02-11 0:31 GMT+01:00 Mike Heffner <m...@librato.com>: > Jeff, > > We have both commitlog and data on a 4TB EBS with 10k IOPS. > > Mike > > On Wed, Feb 10, 2016 at 5:28 PM, Jeff Jirsa <jeff.ji...@crowdstrike.com> > wrote: >> >> What disk size are you using? >> >> >> >> From: Mike Heffner >> Reply-To: "user@cassandra.apache.org" >> Date: Wednesday, February 10, 2016 at 2:24 PM >> To: "user@cassandra.apache.org" >> Cc: Peter Norton >> Subject: Re: Debugging write timeouts on Cassandra 2.2.5 >> >> Paulo, >> >> Thanks for the suggestion, we ran some tests against CMS and saw the same >> timeouts. On that note though, we are going to try doubling the instance >> sizes and testing with double the heap (even though current usage is low). >> >> Mike >> >> On Wed, Feb 10, 2016 at 3:40 PM, Paulo Motta <pauloricard...@gmail.com> >> wrote: >>> >>> Are you using the same GC settings as the staging 2.0 cluster? If not, >>> could you try using the default GC settings (CMS) and see if that changes >>> anything? This is just a wild guess, but there were reports before of >>> G1-caused instabilities with small heap sizes (< 16GB - see CASSANDRA-10403 >>> for more context). Please ignore if you already tried reverting back to CMS. >>> >>> 2016-02-10 16:51 GMT-03:00 Mike Heffner <m...@librato.com>: >>>> >>>> Hi all, >>>> >>>> We've recently embarked on a project to update our Cassandra >>>> infrastructure running on EC2. We are long time users of 2.0.x and are >>>> testing out a move to version 2.2.5 running on VPC with EBS. Our test setup >>>> is a 3 node, RF=3 cluster supporting a small write load (mirror of our >>>> staging load). >>>> >>>> We are writing at QUORUM and while p95's look good compared to our >>>> staging 2.0.x cluster, we are seeing frequent write operations that time >>>> out >>>> at the max write_request_timeout_in_ms (10 seconds). CPU across the cluster >>>> is < 10% and EBS write load is < 100 IOPS. Cassandra is running with the >>>> Oracle JDK 8u60 and we're using G1GC and any GC pauses are less than 500ms. >>>> >>>> We run on c4.2xl instances with GP2 EBS attached storage for data and >>>> commitlog directories. The nodes are using EC2 enhanced networking and have >>>> the latest Intel network driver module. We are running on HVM instances >>>> using Ubuntu 14.04.2. >>>> >>>> Our schema is 5 tables, all with COMPACT STORAGE. Each table is similar >>>> to the definition here: >>>> https://gist.github.com/mheffner/4d80f6b53ccaa24cc20a >>>> >>>> This is our cassandra.yaml: >>>> https://gist.github.com/mheffner/fea80e6e939dd483f94f#file-cassandra-yaml >>>> >>>> Like I mentioned we use 8u60 with G1GC and have used many of the GC >>>> settings in Al Tobey's tuning guide. This is our upstart config with JVM >>>> and >>>> other CPU settings: https://gist.github.com/mheffner/dc44613620b25c4fa46d >>>> >>>> We've used several of the sysctl settings from Al's guide as well: >>>> https://gist.github.com/mheffner/ea40d58f58a517028152 >>>> >>>> Our client application is able to write using either Thrift batches >>>> using Asytanax driver or CQL async INSERT's using the Datastax Java driver. >>>> >>>> For testing against Thrift (our legacy infra uses this) we write batches >>>> of anywhere from 6 to 1500 rows at a time. Our p99 for batch execution is >>>> around 45ms but our maximum (p100) sits less than 150ms except when it >>>> periodically spikes to the full 10seconds. >>>> >>>> Testing the same write path using CQL writes instead demonstrates >>>> similar behavior. Low p99s except for periodic full timeouts. We enabled >>>> tracing for several operations but were unable to get a trace that >>>> completed >>>> successfully -- Cassandra started logging many messages as: >>>> >>>> INFO [ScheduledTasks:1] - MessagingService.java:946 - _TRACE messages >>>> were dropped in last 5000 ms: 52499 for internal timeout and 0 for cross >>>> node timeout >>>> >>>> And all the traces contained rows with a "null" source_elapsed row: >>>> https://gist.githubusercontent.com/mheffner/1d68a70449bd6688a010/raw/0327d7d3d94c3a93af02b64212e3b7e7d8f2911b/trace.out >>>> >>>> >>>> We've exhausted as many configuration option permutations that we can >>>> think of. This cluster does not appear to be under any significant load and >>>> latencies seem to largely fall in two bands: low normal or max timeout. >>>> This >>>> seems to imply that something is getting stuck and timing out at the max >>>> write timeout. >>>> >>>> Any suggestions on what to look for? We had debug enabled for awhile but >>>> we didn't see any msg that pointed to something obvious. Happy to provide >>>> any more information that may help. >>>> >>>> We are pretty much at the point of sprinkling debug around the code to >>>> track down what could be blocking. >>>> >>>> >>>> Thanks, >>>> >>>> Mike >>>> >>>> -- >>>> >>>> Mike Heffner <m...@librato.com> >>>> Librato, Inc. >>>> >>> >> >> >> >> -- >> >> Mike Heffner <m...@librato.com> >> Librato, Inc. >> > > > > -- > > Mike Heffner <m...@librato.com> > Librato, Inc. > -- Close the World, Open the Net http://www.linux-wizard.net
