Cache physical numbers of often used data pages to reduce number of fetches of
pointer pages
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Key: CORE-5441
URL: http://tracker.firebirdsql.org/browse/CORE-5441
Project: Firebird Core
Issue Type: Improvement
Components: Engine
Reporter: Vlad Khorsun
When engine need to fetch some data page by its logical number (sequence number
of DP in relation) it should fetch corresponding PP
first and look for slot with physical number of given DP. I.e. engine always
needs to do two fetches from the page cache to read any row.
Cost of page fetch is small (ideally 2 CAS instructions) but not zero,
especially in highly loaded multy-CPU environment. Also, pointer
pages is a very "hot" pages and many readers could force writers to wait.
Note, mapping of logical data page number to physical numbers is more-or-less
stable.
Obviously, caching of that mapping information could reduce number of fetches
of PP and lower contention in page cache.
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