session: switch to pessimistic txn mode for autocommit statement retry. #18952
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jackysp
reviewed
Aug 3, 2020
It's possible that the TiKV is configured to disable pessimistic transactions. |
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/run-all-tests |
Codecov Report
@@ Coverage Diff @@
## master #18952 +/- ##
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Coverage 79.5369% 79.5369%
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Files 548 548
Lines 149044 149044
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Hits 118545 118545
Misses 20995 20995
Partials 9504 9504 |
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/release |
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LGTM |
ti-srebot
approved these changes
Aug 4, 2020
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/merge |
ti-srebot
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the
status/can-merge
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Your auto merge job has been accepted, waiting for:
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/run-all-tests |
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/run-cherry-picker |
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cherry pick to release-4.0 in PR #19796 |
ti-srebot
pushed a commit
to ti-srebot/tidb
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Sep 4, 2020
Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
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What problem does this PR solve?
Optimize high conflicting autocommit DML.
What is changed and how it works?
Autocommit statements always use optimistic transaction mode, but when the conflict rate is high (zipfian distribution), it may retry too many times.
Switch to pessimistic transaction mode for retry can reduce retry cost.
Check List
Tests
benchmark ycsb zipfian workload and compare the result.
There is no error anymore and the performance increased more than 200%.
Release note