planner: increase default concurrency factor of cost computing#11752
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@@ Coverage Diff @@
## master #11752 +/- ##
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- Coverage 81.776% 81.5477% -0.2284%
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Files 434 433 -1
Lines 94107 93506 -601
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- Hits 76957 76252 -705
- Misses 11684 11838 +154
+ Partials 5466 5416 -50 |
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/run-all-tests |
alivxxx
reviewed
Aug 16, 2019
| IndexReader_11 1104.45 root index:Selection_10 | ||
| └─Selection_10 1104.45 cop lt(test.access_path_selection.b, 3) | ||
| └─IndexScan_9 3323.33 cop table:access_path_selection, index:a, b, range:[-inf,3), keep order:false, stats:pseudo | ||
| CREATE TABLE `outdated_statistics` ( |
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Because this case is intended to test that planner would prefer idx_ab over idx_a, but it is hard to say whether double read using idx_ab is better than table scan or not. With the new concurrency factor, planner would prefer table scan, because there are only 6 rows in total.
alivxxx
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Aug 16, 2019
alivxxx
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/run-all-tests |
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What problem does this PR solve?
#10581 incurs 2.19% performance regression of oltp_read_write workload, this PR resolves this regression.
What is changed and how it works?
The performance regression is caused by the fact that: oltp_read_write contains a class of aggregation quires without Group By, the new cost model would prefer HashAgg which would run in parallel, while the old cost model prefers single-threaded StreamAgg. According to the actual benchmark, single-threaded StreamAgg is a little bit faster than multi-threaded HashAgg for this kind of query.
This PR adjust default concurrency factor to make planner prefer StreamAgg for this kind of query.
Check List
Tests
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