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base repository: postgresql-cfbot/postgresql
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  • 3 commits
  • 5 files changed
  • 2 contributors

Commits on Aug 31, 2025

  1. PGReserveSemaphores() called from CreateSharedMemoryAndSemaphores() 

    Before e256266, PGReserveSemaphores()
was required to be called before SpinlockSemaInit() since spinlocks may
be implemented using semaphores on some platforms.  SpinlockSemaInit()
was required to be called before InitShmemAllocation() since the latter
initialized a spinlock to synchronize shared memory allocations.
e256266 removed the call to
SpinlockSemaInit() from CreateSharedMemoryAndSemaphores() but left the
call to PGReserveSemaphores() in CreateSharedMemoryAndSemaphores(), even
though it fits in CreateOrAttachShmemStructs() along with the calls to
other functions allocating shared memory structures. Add a comment
explaining this absurdity.

To be backpatched to PG 18.

Author: Ashutosh Bapat <[email protected]>
Discussion: https://www.postgresql.org/message-id/CAExHW5seSZpPx-znjidVZNzdagGHOk06F+Ds88MpPUbxd1kTaA@mail.gmail.com
    @ashutosh-bapat
    ashutosh-bapat authored and Commitfest Bot committed Aug 31, 2025
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  2. Refactor shared memory allocation for semaphores 

    Before e256266 spinlocks were
implemented using semaphores on some platforms. Hence
PGReserveSemaphores() was required to be called before
SpinlockSemaInit().  SpinlockSemaInit() was required to be called before
InitShmemAllocation() since the latter initialized a spinlock to
synchronize shared memory allocations.  A cyclic dependency existed
because PGReserveSemaphores() uses shared memory for semaphores on some
platforms. It was broken by letting PGReserveSemaphores() allocate
shared memory without a spinlock using ShmemAllocUnlocked().  After
e256266, spinlocks are not implemented
using semaphores at all. This allows us to eliminate the need to
estimate and allocate shared memory required by semaphores specially and
treat them similar to the other shared memory structures.

Since the semaphores are used only in PGPROC array, it makes more sense
to estimate size of memory required by semaphores to go along with the
estimation of memory required for that array in ProcGlobalShmemSize().
Similarly, it makes sense to have the actual shared memory allocations
for both to be collocated in InitProcGlobal().

With that change CalculateShmemSize() does not need to know about the
number of semaphores to be allocated, eliminating other asymmetry.
InitializeShmemGUCs() which used to get the number of semaphores through
CalculateShmemSize() now fetches that value separately.

Author: Ashutosh Bapat <[email protected]>
Discussion: https://www.postgresql.org/message-id/CAExHW5seSZpPx-znjidVZNzdagGHOk06F+Ds88MpPUbxd1kTaA@mail.gmail.com
    @ashutosh-bapat
    ashutosh-bapat authored and Commitfest Bot committed Aug 31, 2025
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  3. [CF 5997] Treat semaphores similar to other shared memory structures 

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

https://commitfest.postgresql.org/patch/5997

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/CAExHW5uD95UnKdk4Y2rq-yELK6VMXN1bGfrr9o58=BBower3yg@mail.gmail.com
Author(s): Ashutosh Bapat
    Commitfest Bot committed Aug 31, 2025
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