session: switch to pessimistic txn mode for autocommit statement retry. (#18952) #19796
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Signed-off-by: ti-srebot <ti-srebot@pingcap.com>
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youjiali1995
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Sep 4, 2020
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cherry-pick #18952 to release-4.0
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