Have you tried increasing KeysCachedFraction?
On Tue, Feb 16, 2010 at 6:15 PM, Weijun Li <weiju...@gmail.com> wrote: > Still have high read latency with 50mil records in the 2-node cluster > (replica 2). I restarted both nodes but read latency is still above 60ms and > disk i/o saturation is high. Tried compact and repair but doesn't help much. > When I reduced the client threads from 15 to 5 it looks a lot better but > throughput is kind of low. I changed using flushing thread of 16 instead the > defaulted 8, could that cause the disk saturation issue? > > For benchmark with decent throughput and latency, how many client threads do > they use? Can anyone share your storage-conf.xml in well-tuned high volume > cluster? > > -Weijun > > On Tue, Feb 16, 2010 at 10:31 AM, Stu Hood <stu.h...@rackspace.com> wrote: >> >> > After I ran "nodeprobe compact" on node B its read latency went up to >> > 150ms. >> The compaction process can take a while to finish... in 0.5 you need to >> watch the logs to figure out when it has actually finished, and then you >> should start seeing the improvement in read latency. >> >> > Is there any way to utilize all of the heap space to decrease the read >> > latency? >> In 0.5 you can adjust the number of keys that are cached by changing the >> 'KeysCachedFraction' parameter in your config file. In 0.6 you can >> additionally cache rows. You don't want to use up all of the memory on your >> box for those caches though: you'll want to leave at least 50% for your OS's >> disk cache, which will store the full row content. >> >> >> -----Original Message----- >> From: "Weijun Li" <weiju...@gmail.com> >> Sent: Tuesday, February 16, 2010 12:16pm >> To: cassandra-user@incubator.apache.org >> Subject: Re: Cassandra benchmark shows OK throughput but high read latency >> (> 100ms)? >> >> Thanks for for DataFileDirectory trick and I'll give a try. >> >> Just noticed the impact of number of data files: node A has 13 data files >> with read latency of 20ms and node B has 27 files with read latency of >> 60ms. >> After I ran "nodeprobe compact" on node B its read latency went up to >> 150ms. >> The read latency of node A became as low as 10ms. Is this normal behavior? >> I'm using random partitioner and the hardware/JVM settings are exactly the >> same for these two nodes. >> >> Another problem is that Java heap usage is always 900mb out of 6GB? Is >> there >> any way to utilize all of the heap space to decrease the read latency? >> >> -Weijun >> >> On Tue, Feb 16, 2010 at 10:01 AM, Brandon Williams <dri...@gmail.com> >> wrote: >> >> > On Tue, Feb 16, 2010 at 11:56 AM, Weijun Li <weiju...@gmail.com> wrote: >> > >> >> One more thoughts about Martin's suggestion: is it possible to put the >> >> data files into multiple directories that are located in different >> >> physical >> >> disks? This should help to improve the i/o bottleneck issue. >> >> >> >> >> > Yes, you can already do this, just add more <DataFileDirectory> >> > directives >> > pointed at multiple drives. >> > >> > >> >> Has anybody tested the row-caching feature in trunk (shoot for 0.6?)? >> > >> > >> > Row cache and key cache both help tremendously if your read pattern has >> > a >> > decent repeat rate. Completely random io can only be so fast, however. >> > >> > -Brandon >> > >> >> > >
