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Type:
Bug
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Resolution: Done
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Priority:
Major - P3
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Affects Version/s: 2.5.5
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Component/s: Concurrency, Querying
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Environment:Linux ip-10-232-37-146.ec2.internal 2.6.32-358.14.1.el6.x86_64 #1 SMP Mon Jun 17 15:54:20 EDT 2013 x86_64 x86_64 x86_64 GNU/Linux
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ALL
My query concurrency tests showed up a clear regression when different kind of queries are executed concurrently.
I relied on git bisect to find out where the problem was, starting from
Good revision: 06851f4859a61019a17147ea96c4e6d9462f354b Bad revision: f2ece186b189b2b9d09636c708f768fb3822b511
The commit that caused the regression is:
# git bisect good 2bee3f018b8d4351f8261c405adcdff44c7f9a70
3b3c25e571852893373ae2e2b361397b260687c9 is the first bad commit
commit 3b3c25e571852893373ae2e2b361397b260687c9
Author: Hari Khalsa <hkhalsa@10gen.com>
Date: Mon Jan 27 18:01:26 2014 -0500
SERVER-12460 faster count for simple queries
I more carefully looked at the server logs and realized there's something unusual:
2014-01-30T14:48:52.824-0500 [conn133] command test1.$cmd command: { count: "QA408", query: { timestamp: { $gte: new Date(1388927893439), $lte: new Date(1388999113439) } }, limit: 1 } keyUpdates:0 numYields:22 locks(micros) r:5722 reslen:48 111ms
2014-01-30T14:48:52.835-0500 [conn129] command test1.$cmd command: { count: "QA408", query: { timestamp: { $gte: new Date(1389166093427), $lte: new Date(1389327733427) } }, limit: 1 } keyUpdates:0 numYields:50 locks(micros) r:6720 reslen:48 129ms
2014-01-30T14:48:52.847-0500 [conn119] command test1.$cmd command: { count: "QA408", query: { timestamp: { $gte: new Date(1390298233437), $lte: new Date(1390424353437) } }, limit: 1 } keyUpdates:0 numYields:40 locks(micros) r:6359 reslen:48 136ms
Lots of yields – apparently this didn't happen before the change.
CPU profiling via gperftools confirmsthe suspects, FWIW.
(pprof) list mongo::PlanExecutor::getNext
[...]
. . 79: for (;;) {
. . 80: // Yield, if we can yield ourselves.
76 337 81: if (NULL != _yieldPolicy.get() && _yieldPolicy->shouldYield()) {
. 166 82: saveState();
23 4884 83: _yieldPolicy->yield();
4 8 84: if (_killed) { return Runner::RUNNER_DEAD; }
. 765 85: restoreState();
. . 86: }
[...]
- related to
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SERVER-13336 Count with no results, never yields
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- Closed
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