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Type:
Bug
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Resolution: Duplicate
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Priority:
Major - P3
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None
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Affects Version/s: 2.2.0-rc0
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Component/s: Index Maintenance
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None
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Environment:Linux 3.2.0-27-generic #43-Ubuntu SMP Fri Jul 6 14:25:57 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
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ALL
While responding to this thread, I realized that b-tree scans were happening much slower in 2.2.0-rc0 than they were in the stable 2.0 branch.
I'm attaching the test script, which is also available at https://gist.github.com/3184175.
Here is a comparison of 2.0 and 2.2.0-rc1-pre-:
$ mongo reads.js MongoDB shell version: 2.0.6 connecting to: test ---- One batch of 100 queries in the 75-100k range ---- batch 1 nscanned: 1269469 total time: 3.379 btree.accesses: 0 btree.hits: 0 btree.misses: 0 btree.resets: 0 btree.missRatio: 0 ---- Four batches of 25 queries in the 0-25, 25-50, 50-75, and 75-100k ranges ---- batch 1 nscanned: 324675 batch 2 nscanned: 974675 batch 3 nscanned: 975800 batch 4 nscanned: 325819 total time: 6.688 btree.accesses: 0 btree.hits: 0 btree.misses: 0 btree.resets: 0 btree.missRatio: 0 $ mongo reads.js MongoDB shell version: 2.2.0-rc1-pre- connecting to: test ---- One batch of 100 queries in the 75-100k range ---- batch 1 nscanned: 1269469 total time: 5.956 btree.accesses: 0 btree.hits: 0 btree.misses: 0 btree.resets: 0 btree.missRatio: 0 ---- Four batches of 25 queries in the 0-25, 25-50, 50-75, and 75-100k ranges ---- batch 1 nscanned: 324675 batch 2 nscanned: 974675 batch 3 nscanned: 975800 batch 4 nscanned: 325819 total time: 11.918 btree.accesses: 0 btree.hits: 0 btree.misses: 0 btree.resets: 0 btree.missRatio: 0
Andy initially suspected this might be related to SERVER-6572, and suggested that I re-run this benchmark after setting Record::MemoryTrackingEnabled to false in src/mongo/db/record.cpp. That marginally increased performance, but the results are still much slower than 2.0. Here are those results are:
$ mongo reads.js MongoDB shell version: 2.2.0-rc1-pre- with memory tracking disabled connecting to: test batch 1 nscanned: 1269469 total time: 5.246 btree.accesses: 0 btree.hits: 0 btree.misses: 0 btree.resets: 0 btree.missRatio: 0 batch 1 nscanned: 324675 batch 2 nscanned: 974675 batch 3 nscanned: 975800 batch 4 nscanned: 325819 total time: 10.574 btree.accesses: 0 btree.hits: 0 btree.misses: 0 btree.resets: 0 btree.missRatio: 0 $ mongo reads.js MongoDB shell version: 2.2.0-rc1-pre- connecting to: test batch 1 nscanned: 1269469 total time: 5.756 btree.accesses: 0 btree.hits: 0 btree.misses: 0 btree.resets: 0 btree.missRatio: 0 batch 1 nscanned: 324675 batch 2 nscanned: 974675 batch 3 nscanned: 975800 batch 4 nscanned: 325819 total time: 11.91 btree.accesses: 0 btree.hits: 0 btree.misses: 0 btree.resets: 0 btree.missRatio: 0
- duplicates
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- Closed
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