If you ran the workload with file channel and then took 10 thread dumps I think we'd have enough to understand what is going on.
Brock On Mon, Jul 9, 2012 at 11:49 AM, Juhani Connolly <[email protected]> wrote: > It is currently pushing only 10 events per second or so(roughly 250 bytes > per event). This is with datadir/checkpoint on the same directory. Of course > the fact that there is a tail process running and that tomcat is also > writing out logs is without a doubt compounding the problem somewhat. > > I haven't taken a serious look at thread dumps of the file channel since I > don't have a thorough understanding of it. However analysis has involved > trying varying numbers of sinks(no throughput difference) and replacing with > memory channel(which easily handles the 650 ish requests per second we have > per server for the particular api, no problems even with a single sink). > > Since you say there's heavy fsyncing, and with 7200rpm disks, each seek will > have an average latency of 4.16ms, so for alternating seeks between the > checkpoint and the data dir, if each of those writes happens in order, > you're already limited to best case of barely more than 100 events per > second. Our experience so far has shown it to be significantly less. > > I do believe that batching a bunch of puts or takes with a single commit > together as two seeks followed by writes(or one if we can only use a single > storage file) could give significant returns when paired with a batching > sink/source(which many already do... Requesting multiple items at a time). > > If there is any specific data you would like I would be happy to try and > provide it. > > > On 07/09/2012 05:22 PM, Brock Noland wrote: > > On Mon, Jul 9, 2012 at 8:51 AM, Juhani Connolly > <[email protected]> wrote: >> >> - Intended setup with flume was a file channel connected to an avro sink. >> With only a single disk available, it is extremely slow. JDBC channel is >> also extremely slow, and MemoryChannel will fill up and start refusing puts >> as soon as a network issue comes up. > > > Have you taken a few thread dumps or done other analysis? When you say > "extremely slow" what do you mean? Configured for no dataloss FileChannel is > going to be doing a lot of fsync'ing so I am not surprised it's slow. That > is a property of disks not FileChannel. I think we should use group commit > but that shouldn't make it 10x faster. > > Brock > > > -- Apache MRUnit - Unit testing MapReduce - http://incubator.apache.org/mrunit/
