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From: Tomas Vondra <[email protected]>
To: David Rowley <[email protected]>
To: Tomas Vondra <[email protected]>
Cc: [email protected]
Subject: Re: pgsql: Improve accounting for memory used by shared hash tables
Date: Fri, 4 Apr 2025 02:41:40 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<CAApHDvriCiNkm=v521AP6PKPfyWkJ++jqZ9eqX4cXnhxLv8w-A@mail.gmail.com>
	<[email protected]>

On 4/4/25 01:43, Tomas Vondra wrote:
> On 4/4/25 00:57, David Rowley wrote:
>> On Thu, 3 Apr 2025 at 04:16, Tomas Vondra <[email protected]> wrote:
>>> Improve accounting for memory used by shared hash tables
>>
>> I've not looked into why, but this is causing an issue in the
>> join_rel_hash during add_join_rel(). See the attached script.
>>
>> ERROR:  pfree called with invalid pointer 0x60a15edc44e0 (header
>> 0x0000002000000008)
>>
> 
> Thanks for the report and reproducer. I'll take a look tomorrow.
> 

I took a quick look, and I think the reason is fairly simple - the
commit allocates the header and the directory as a single chunk. And for
shared hash tables that's fine, because those have non-expandable
directory. But the patch does the same thing for non-shared hash tables
(not intentionally), which means that if we end up expanding the hash,
it fails in dir_realloc(). Because hashp->dir is not a separately
allocated chunk.

This is clearly a bug in the patch, I should have caught this during a
review. But I'm also quite surprised none of the regression tests seems
to expand the hash table ...

I'll think about a way to fix this tomorrow.

-- 
Tomas Vondra

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