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https://issues.apache.org/jira/browse/CASSANDRA-5932?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13781557#comment-13781557
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Hubert Sugeng edited comment on CASSANDRA-5932 at 9/30/13 1:26 AM:
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Definitely the best results seen so far! Nice work!
In my mind, during the killing of the node, I expected "ALWAYS" to have
negligible impact, or at least the smallest impact of all of the other values.
However, red (90%), and purple (75%) is having a smaller impact. Seems fishy.
Do I misunderstand the intention of the "ALWAYS" setting?
(Edited to clarify the period I'm talking about.)
was (Author: hubez):
Definitely the best results seen so far! Nice work!
In my mind, I expected "ALWAYS" to have negligible impact, or at least the
smallest impact of all of the other values. However, red (90%), and purple
(75%) is having a smaller impact. Seems fishy. Do I misunderstand the intention
of the "ALWAYS" setting?
> Speculative read performance data show unexpected results
> ---------------------------------------------------------
>
> Key: CASSANDRA-5932
> URL: https://issues.apache.org/jira/browse/CASSANDRA-5932
> Project: Cassandra
> Issue Type: Bug
> Reporter: Ryan McGuire
> Assignee: Aleksey Yeschenko
> Fix For: 2.0.2
>
> Attachments: 5932-6692c50412ef7d.png, 5932.ded39c7e1c2fa.logs.tar.gz,
> 5932.txt, 5933-128_and_200rc1.png, 5933-7a87fc11.png, 5933-logs.tar.gz,
> 5933-randomized-dsnitch-replica.2.png, 5933-randomized-dsnitch-replica.3.png,
> 5933-randomized-dsnitch-replica.png, compaction-makes-slow.png,
> compaction-makes-slow-stats.png, eager-read-looks-promising.png,
> eager-read-looks-promising-stats.png, eager-read-not-consistent.png,
> eager-read-not-consistent-stats.png, node-down-increase-performance.png
>
>
> I've done a series of stress tests with eager retries enabled that show
> undesirable behavior. I'm grouping these behaviours into one ticket as they
> are most likely related.
> 1) Killing off a node in a 4 node cluster actually increases performance.
> 2) Compactions make nodes slow, even after the compaction is done.
> 3) Eager Reads tend to lessen the *immediate* performance impact of a node
> going down, but not consistently.
> My Environment:
> 1 stress machine: node0
> 4 C* nodes: node4, node5, node6, node7
> My script:
> node0 writes some data: stress -d node4 -F 30000000 -n 30000000 -i 5 -l 2 -K
> 20
> node0 reads some data: stress -d node4 -n 30000000 -o read -i 5 -K 20
> h3. Examples:
> h5. A node going down increases performance:
> !node-down-increase-performance.png!
> [Data for this test
> here|http://ryanmcguire.info/ds/graph/graph.html?stats=stats.eager_retry.node_killed.just_20.json&metric=interval_op_rate&operation=stress-read&smoothing=1]
> At 450s, I kill -9 one of the nodes. There is a brief decrease in performance
> as the snitch adapts, but then it recovers... to even higher performance than
> before.
> h5. Compactions make nodes permanently slow:
> !compaction-makes-slow.png!
> !compaction-makes-slow-stats.png!
> The green and orange lines represent trials with eager retry enabled, they
> never recover their op-rate from before the compaction as the red and blue
> lines do.
> [Data for this test
> here|http://ryanmcguire.info/ds/graph/graph.html?stats=stats.eager_retry.compaction.2.json&metric=interval_op_rate&operation=stress-read&smoothing=1]
> h5. Speculative Read tends to lessen the *immediate* impact:
> !eager-read-looks-promising.png!
> !eager-read-looks-promising-stats.png!
> This graph looked the most promising to me, the two trials with eager retry,
> the green and orange line, at 450s showed the smallest dip in performance.
> [Data for this test
> here|http://ryanmcguire.info/ds/graph/graph.html?stats=stats.eager_retry.node_killed.json&metric=interval_op_rate&operation=stress-read&smoothing=1]
> h5. But not always:
> !eager-read-not-consistent.png!
> !eager-read-not-consistent-stats.png!
> This is a retrial with the same settings as above, yet the 95percentile eager
> retry (red line) did poorly this time at 450s.
> [Data for this test
> here|http://ryanmcguire.info/ds/graph/graph.html?stats=stats.eager_retry.node_killed.just_20.rc1.try2.json&metric=interval_op_rate&operation=stress-read&smoothing=1]
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