Reduce contention for allocation table lock while database is in stalled
physical backup state
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Key: CORE-4431
URL: http://tracker.firebirdsql.org/browse/CORE-4431
Project: Firebird Core
Issue Type: Improvement
Affects Versions: 3.0 Alpha 2, 3.0 Alpha 1, 2.5.2 Update 1, 2.1.5 Update 1,
2.5.2, 2.1.5
Environment: ClassicServer and SuperClassic modes
Reporter: Vlad Khorsun
In Classic modes (CS\SC) every attachment have its own private cache of
allocation table contents.
Access to allocation table is protected by common allocation table lock (alloc
lock).
Currently, when attachment needs to look for a page number at allocation table,
it acquires alloc lock in SH mode.
But it is not necessary if corresponding part of allocation table is already
cached by attachement as allocation
table entries is never changed, it is only appended.
More, a lot of unnecessary requests for a SH lock not allows writers to proceed
as quick as it can.
The improvement is to introduce additional local (per-attachment) read-write
lock to protect access to the
attachment's private cache of the allocation table. It allows to significantly
lower contention on global lock.
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