From: Nathan Bossart <nathandbossart@gmail.com>
To: Sami Imseih <samimseih@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Rahila Syed <rahilasyed90@gmail.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Improve LWLock tranche name visibility across backends
Date: Tue, 26 Aug 2025 15:14:39 -0500
Message-ID: <aK4Vr0puSQqPI5vS@nathan> (raw)
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On Tue, Aug 26, 2025 at 02:56:22PM -0500, Sami Imseih wrote:
> Here is v12 that replaces the LWLock to access the shared memory with a
> ShmemLock and implements a local counter.
This looks much closer to what I was imagining.
/* Initialize the LWLock tranche for the DSA. */
- dsa_state->tranche = LWLockNewTrancheId();
+ dsa_state->tranche = LWLockNewTrancheId(dsa_state->tranche_name);
sprintf(dsa_state->tranche_name, "%s%s", name, DSMR_DSA_TRANCHE_SUFFIX);
- LWLockRegisterTranche(dsa_state->tranche, dsa_state->tranche_name);
/* Initialize the LWLock tranche for the dshash table. */
- dsh_state->tranche = LWLockNewTrancheId();
+ dsh_state->tranche = LWLockNewTrancheId(dsh_state->tranche_name);
strcpy(dsh_state->tranche_name, name);
- LWLockRegisterTranche(dsh_state->tranche, dsh_state->tranche_name);
We probably need to do the sprintf/strcpy before LWLockNewTrancheId().
Also, I'm thinking we should just use the same tranche for both the DSA and
the dshash table [0] to evade the DSMR_DSA_TRANCHE_SUFFIX problem, i.e.,
those tranche names potentially require more space.
+ /* Space for name of each tranche. */
+ size = add_size(size, mul_size(MAX_NAMED_TRANCHES, MAX_NAMED_TRANCHES));
Presumably one of the mul_size() arguments should be
MAX_NAMED_TRANCHES_NAME_LEN.
+NamedLWLockTrancheArray "Waiting to access the named LWLock tranches array."
+PG_LWLOCK(54, NamedLWLockTrancheArray)
These can be removed now, right?
[0] https://postgr.es/m/aKzIg1JryN1qhNuy%40nathan
--
nathan
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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, samimseih@gmail.com, tgl@sss.pgh.pa.us, andres@anarazel.de, bertranddrouvot.pg@gmail.com, rahilasyed90@gmail.com
Subject: Re: Improve LWLock tranche name visibility across backends
In-Reply-To: <aK4Vr0puSQqPI5vS@nathan>
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