Increase performance of backout of dead record version (or undo of just created
primary record version) when backversions chain is too long
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Key: CORE-4935
URL: http://tracker.firebirdsql.org/browse/CORE-4935
Project: Firebird Core
Issue Type: Improvement
Components: Engine
Affects Versions: 3.0 Beta 2, 2.5.4, 2.5.3 Update 1, 2.1.7, 3.0 Beta 1,
2.5.3, 2.1.6, 3.0 Alpha 2, 3.0 Alpha 1, 2.5.2 Update 1, 2.1.5 Update 1, 2.5.2,
2.5.1, 2.5.0
Reporter: Vlad Khorsun
Function list_staying() used in backout and undo processes have complexity
O(N^2), where N is the number of back versions.
There is a way to reduce complexity down to O(N) in most cases. Specifically -
when current transaction (which does backout
or undo) already own the record (i.e. primary record version is marked by
current transaction) there is guarantee that no other
transaction will try to backout\undo the record.
Another improvement is to cut and cleanup tail of the back-versions chain at
point where it is legal
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