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base repository: postgresql-cfbot/postgresql
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base: cf/5940~1
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head repository: postgresql-cfbot/postgresql
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compare: cf/5940
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  • 2 commits
  • 24 files changed
  • 2 contributors

Commits on Aug 12, 2025

  1. Implement a DSA for LWLock tranche names 

    Previously, only LWLock tranches registered during postmaster startup were
available to all backends via a tranche name array inherited through fork.
Other backends that wanted to know about a tranche name had to register it
using LWLockRegisterTranche. While this design worked as intended, it was
not ideal because if a backend did not call LWLockRegisterTranche, it would
show a generic "extension" wait_event name in pg_stat_activity instead of
the actual tranche name. This caused inconsistencies with other backends
that registered the tranche name.

Commit fe07100 made dynamic creation of named DSA areas (and dshash)
much simpler for a backend, so it is anticipated that fewer tranche names
will be registered during postmaster startup in the future, with more
registered dynamically. This will make the above issue more common.

To address this, this change introduces a DSA to store LWLock tranche names
after postmaster startup. When a backend looks up a tranche name by tranche ID,
it first checks its local cache; if the name is not found locally, it fetches
it from the DSA and caches it for future lookups.

This also simplifies the API for registering tranche names: all registration
work is now done via LWLockNewTrancheId, which accepts a tranche name. The
LWLockRegisterTranche call is no longer required.

Additionally, while users should not pass arbitrary tranche IDs (that is,
IDs not created via LWLockNewTrancheId) to LWLockInitialize, nothing
technically prevents them from doing so. Therefore, we must continue to
handle such cases gracefully by returning a default "extension" tranche name.

Discussion: https://www.postgresql.org/message-id/flat/CAA5RZ0vvED3naph8My8Szv6DL4AxOVK3eTPS0qXsaKi%3DbVdW2A%40mail.gmail.com
    @samimseih
    samimseih authored and Commitfest Bot committed Aug 12, 2025
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  2. [CF 5940] v6 - Improve LWLock tranche name visibility across backends 

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

https://commitfest.postgresql.org/patch/5940

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/CAA5RZ0siw2MrVjf9iPYRpe8sgZW+TJRqmxKfCr=QS9mX+ZF8Lw@mail.gmail.com
Author(s): Sami Imseih
    Commitfest Bot committed Aug 12, 2025
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