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From Henry May <hj...@us.ibm.com>
Subject Flush on disk writes
Date Wed, 15 Oct 2014 12:55:22 GMT
I have couple of standalone Zookeeper servers that perform very 
differently.  I collected a block io trace using the following:
perf record -a -e "block:block_rq_issue,block:block_rq_complete"

On the fast server, I see lots of sequences that look like this:
            java 32429 [005] 786479.507611: block_rq_issue: 8,0 WS 0 () 
187774376 + 8 [java]
            init     1 [001] 786479.514222: block_rq_complete: 8,0 WS () 
187774376 + 8 [0]
On the slow server I see these additional events:
            java  2209 [007] 254523.025322: block:block_rq_issue: 8,16 FWS 
0 () 18446744073709551615 + 0 [java]
            init     1 [007] 254523.044166: block:block_rq_complete: 8,16 
WS () 0 + 0 [0]

How do I determine what is triggering the flushes on the slow system?

For what it's worth, the slow server is following the best practice 
recommendation of putting the ZK log on a dedicated drive.  The fast 
server is not, because we only have a single disk on that system.

Henry May
IBM InfoSphere Streams Performance
hjmay@us.ibm.com
720-342-8873
Tie: 963-8873

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