From: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
To: "'pgsql-hackers@lists.postgresql.org'"
	<pgsql-hackers@lists.postgresql.org>
Subject: Some shared memory chunks are allocated even if related processes
 won't start
Thread-Topic: Some shared memory chunks are allocated even if related
 processes won't start
Thread-Index: Adpt8+CSxtaAWHAQS3ytcOb4zsqabw==
Date: Mon, 4 Mar 2024 05:26:25 +0000
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--_002_TYCPR01MB12077BFDFBC142086D424FDFEF5232TYCPR01MB12077jp_
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Dear hackers,

While reading codes, I found that ApplyLauncherShmemInit() and AutoVacuumSh=
memInit()
are always called even if they would not be launched.
It may be able to reduce the start time to avoid the unnecessary allocation=
.
However, I know this improvement would be quite small because the allocated=
 chunks are
quite small.

Anyway, there are several ways to fix:

1)
Skip calling ShmemInitStruct() if the related process would not be launched=
.
I think this approach is the easiest way. E.g.,

```
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -962,6 +962,9 @@ ApplyLauncherShmemInit(void)
 {
     bool        found;

+    if (max_logical_replication_workers =3D=3D 0 || IsBinaryUpgrade)
+        return;
+
```

2)
Dynamically allocate the shared memory. This was allowed by recent commit [=
1].
I made a small PoC only for logical launcher to show what I meant. PSA diff=
 file.
Since some processes (backend, apply worker, parallel apply worker, and tab=
lesync worker)
refers the chunk, codes for attachment must be added on the several places.

If you agree it should be fixed, I will create a patch. Thought?

[1]: https://github.com/postgres/postgres/commit/8b2bcf3f287c79eaebf724cba5=
7e5ff664b01e06

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/=20


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	creation-date="Mon, 04 Mar 2024 05:20:42 GMT";
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