Thread

Re: Improve LWLock tranche name visibility across backends

Rahila Syed <rahilasyed90@gmail.com> — 2025-07-15T07:29:04Z

Hi,


>
> Since DSM is not available during postmaster, if we were to create a DSA
> segment in place, similar to what's done in StatsShmemInit(), we would also
> need to ensure that the initial shared memory is sized appropriately. This
> is
> because it would need to be large enough to accommodate all user-defined
> tranches registered during postmaster, without having to rely on new
> dsm segments.
> From my experimentation, this sizing is not as straightforward as simply
> calculating # of tranches * size of a tranche entry.
>
> I still think we should create the dsa during postmaster, as we do with
> StatsShmemInit, but it would be better if postmaster keeps its hands off
> this
> dshash and only normal backends can use them.
>
> Thoughts?
>
>
Since creating a DSA segment in place during Postmaster startup still
requires calculating the size of
the tranche names table including the user-defined tranches, why not use
static shared memory to
pre-allocate a fixed sized table and arrays of size NAMEDATALEN to store
the names?

If a dshash table is used to store tranche names and IDs, where would the
tranche name for this table
be registered?

Thank you,
Rahila Syed