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base repository: postgresql-cfbot/postgresql
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head repository: postgresql-cfbot/postgresql
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compare: cf/5928
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  • 4 commits
  • 8 files changed
  • 2 contributors

Commits on Aug 9, 2025

  1. Eliminate the freelist from the buffer manager and depend on clock-sweep 

    This set of changes removes the list of available buffers and instead
simply uses the clock-sweep algorithm to find and return an available
buffer.  While on the surface this appears to be removing an
optimization it is in fact eliminating code that induces overhead in the
form of synchronization that is problemmatic for multi-core systems.
This also removes the have_free_buffer() function and simply caps the
pg_autoprewarm process to at most NBuffers.
    @gburd
    gburd authored and Commitfest Bot committed Aug 9, 2025
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  2. Remove the buffer_strategy_lock and make the clock hand a 64 bit atomic 

    Change nextVictimBuffer to an atomic uint64 and simply atomically
increment it by 1 at each tick.  The next victim buffer is the the value
of nextVictimBuffer modulo the number of buffers (NBuffers).  The number
of complete passes of the clock-sweep hand is nextVictimBuffer divided
by NBuffers. Wrap-around of nextVictimBuffer would require 10 years at
~59 billion ticks per-second without restart, so unlikely that we ignore
that case entirely.

With the removal of the freelist and completePasses none of remaining
items in the BufferStrategyControl structure require strict coordination
and so it is possible to eliminate the buffer_strategy_lock as well.
    @gburd
    gburd authored and Commitfest Bot committed Aug 9, 2025
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  3. Abstract clock-sweep buffer replacement algorithm 

    Re-author the clock-sweep algorithm such that it maintains its own state
and has a well defined API.
    @gburd
    gburd authored and Commitfest Bot committed Aug 9, 2025
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  4. [CF 5928] v11 - Remove freelist and the buffer_strategy_lock 

    This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/5928

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/[email protected]
Author(s): Greg Burd
    Commitfest Bot committed Aug 9, 2025
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