Re: Amcheck verification of GiST and GIN

Hi!

On Mon, 5 Aug 2024 at 20:05, Tomas Vondra <tomas(at)vondra(dot)me> wrote:
>
> Hi,
>
> I've spent a bit more time looking at the GiST part as part of my
> "parallel GiST build" patch nearby, and I think there's some sort of
> memory leak.
>
> Consider this:
>
> create table t (a text);
>
> insert into t select md5(i::text)
> from generate_series(1,25000000) s(i);
>
> create index on t using gist (a gist_trgm_ops);
>
> select gist_index_check('t_a_idx', true);
>
> This creates a ~4GB GiST trigram index, and then checks it. But that
> gets killed, because of OOM killer. On my test machine it consumes
> ~6.5GB of memory before OOM intervenes.
>
> The memory context stats look like this:
>
> TopPortalContext: 8192 total in 1 blocks; 7680 free (0 chunks); 512 used
> PortalContext: 1024 total in 1 blocks; 616 free (0 chunks); 408
> used: <unnamed>
> ExecutorState: 8192 total in 1 blocks; 4024 free (4 chunks); 4168 used
> printtup: 8192 total in 1 blocks; 7952 free (0 chunks); 240 used
> ExprContext: 8192 total in 1 blocks; 7224 free (10 chunks); 968 used
> amcheck context: 3128950872 total in 376 blocks; 219392 free
> (1044 chunks); 3128731480 used
> ExecutorState: 8192 total in 1 blocks; 7200 free (0 chunks);
> 992 used
> ExprContext: 8192 total in 1 blocks; 7952 free (0 chunks);
> 240 used
> GiST scan context: 22248 total in 2 blocks; 7808 free (8
> chunks); 14440 used
>
> This is from before the OOM kill, but it shows there's ~3GB of memory is
> the amcheck context.
>
> Seems like a memory leak to me - I didn't look at which place leaks.

+ 1, there is a memory leak.

>
>
> regards
>
> --
> Tomas Vondra
>
>

So, I did some testing, and it seems that the tuple returned by
`gistgetadjusted` inside `gist_check_page` is not being freed.

Trivial fix attached.

--
Best regards,
Kirill Reshke