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From: Tom Lane <[email protected]>
To: Michael Paquier <[email protected]>
Cc: Xing Guo <[email protected]>
Cc: [email protected]
Subject: Re: Fix an incorrect assertion condition in mdwritev().
Date: Sun, 26 May 2024 00:08:46 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CACpMh+BM-VgKeO7suPG-VHTtpzJ+zsbDPwVHu42PLp-iTk0z+A@mail.gmail.com>
	<[email protected]>
	<[email protected]>

I wrote:
> Hmm ... I agree that this is better normally.  But there's an
> edge case where it would fail to notice a problem that the
> existing code does notice: if blocknum is close to UINT32_MAX
> and adding nblocks causes it to wrap around to a small value.
> Is there an inexpensive way to catch that?

After a few minutes' thought, how about:

	Assert((uint64) blocknum + (uint64) nblocks <= (uint64) mdnblocks(reln, forknum));

This'd stop being helpful if we ever widen BlockNumber to 64 bits,
but I think that's unlikely.  (Partitioning seems like a better answer
for giant tables.)

			regards, tom lane

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