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help / color / mirror / Atom feedFrom: Antonin Houska <[email protected]>
To: Chao Li <[email protected]>
Cc: Postgres hackers <[email protected]>
Subject: Re: repack: fix uninitialized DecodingWorkerShared.initialized
Date: Wed, 15 Apr 2026 17:07:32 +0200
Message-ID: <26785.1776265652@localhost> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
Chao Li <[email protected]> wrote:
> I have not reviewed the repack-related patches before. Recently, I started trying to understand how repack works and trace through the code.
Thanks, I appreciate that!
> While tracing start_repack_decoding_worker(), I noticed something suspicious:
>
> ```
> seg = dsm_create(size, 0);
> shared = (DecodingWorkerShared *) dsm_segment_address(seg);
> shared->lsn_upto = InvalidXLogRecPtr;
> shared->done = false;
> SharedFileSetInit(&shared->sfs, seg);
> shared->last_exported = -1;
> SpinLockInit(&shared->mutex);
> shared->dbid = MyDatabaseId;
> ```
>
> Here, the code creates a shared-memory segment and lets “shared" point to that memory. It then initializes some fields of “shared". However, later code reads shared->initialized, but this field was not initialized:
The problem was noticed earlier this week and I already posted a fix [1].
> For the fix, since start_repack_decoding_worker() is not on a hot path, I think it is fine to zero the whole shared struct explicitly, and then initialize the non-zero fields afterwards.
Although not strongly, I prefer setting individual fields explicitly.
[1] https://www.postgresql.org/message-id/182883.1776073323%40localhost
--
Antonin Houska
Web: https://www.cybertec-postgresql.com
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To: [email protected]
Cc: [email protected], [email protected], [email protected]
Subject: Re: repack: fix uninitialized DecodingWorkerShared.initialized
In-Reply-To: <26785.1776265652@localhost>
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