Re: Improve LWLock tranche name visibility across backends

On Mon, Jul 14, 2025 at 03:45:02PM -0500, Sami Imseih wrote:
>> Ah, I missed the problem with postmaster. Could we have the first backend
>> that needs to access the table be responsible for creating it and
>> populating it with the built-in/requested-at-startup entries?
>
> We can certainly maintain a flag in the shared state that is set once
> the first backend loads all the tranches in shared memory. That did not
> cross my mind, but it feels wrong to offload such responsibility to a
> normal backend.

Well, we already need each backend to either initialize or attach to the
dshash table, and the initialization would only ever happen once on a
running server. Adding a new initialization step to bootstrap the built-in
and registered-at-startup tranche names doesn't seem like that much of a
leap to me.

Another random thought: I worry that the dshash approach might be quite a
bit slower, and IIUC we just need to map an integer to a string. Maybe we
should just use a DSA for LWLockTrancheNames. IOW we'd leave it as a char
** but put it in shared memory.

--
nathan