Horton

Re: Improve LWLock tranche name visibility across backends

Sami Imseih <samimseih@gmail.com>

View thread View on postgr.es
From: Sami Imseih <samimseih@gmail.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Rahila Syed <rahilasyed90@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2025-08-22T20:49:38Z
Lists: pgsql-hackers 
On Fri, Aug 22, 2025 at 3:01 PM Sami Imseih <samimseih@gmail.com> wrote:
>
> >> If there is agreement on setting limits, may I propose
> >> 1024 tranches and NAMEDATALEN. Both seem reasonably sufficient.
>
> > Let's proceed with that approach for now.  We can worry about the exact
> > limits once this is closer to commit.
>
> v11 implements the fixed size shared memory as discussed.

One point I did not make earlier is that the tranche name lengths will
need to be as long as we allow in dsm_registry.c.

```
#define DSMR_NAME_LEN 128

#define DSMR_DSA_TRANCHE_SUFFIX " DSA"
#define DSMR_DSA_TRANCHE_SUFFIX_LEN (sizeof(DSMR_DSA_TRANCHE_SUFFIX) - 1)
#define DSMR_DSA_TRANCHE_NAME_LEN (DSMR_NAME_LEN + DSMR_DSA_TRANCHE_SUFFIX_LEN)
```

We should make the limits external (in lwlock.h) and dsa_registery.c
can enforce
based on those values.

--
Sami

Commits

  1. test_dsa: Avoid leaking LWLock tranches.

  2. Teach DSM registry to ERROR if attaching to an uninitialized entry.

  3. Add a test harness for the LWLock tranche code.

  4. Revert recent change to RequestNamedLWLockTranche().

  5. Move dynamically-allocated LWLock tranche names to shared memory.

  6. Prepare DSM registry for upcoming changes to LWLock tranche names.

  7. Add GetNamedDSA() and GetNamedDSHash().