Re: brininsert optimization opportunity

On 11/27/23 08:37, Richard Guo wrote:
>
> On Mon, Nov 27, 2023 at 1:53 PM Soumyadeep Chakraborty
> <soumyadeep2007(at)gmail(dot)com <mailto:soumyadeep2007(at)gmail(dot)com>> wrote:
>
> On Sun, Nov 26, 2023 at 9:28 PM Richard Guo <guofenglinux(at)gmail(dot)com
> <mailto:guofenglinux(at)gmail(dot)com>> wrote:
> > It seems that we have an oversight in this commit.  If there is no
> tuple
> > that has been inserted, we wouldn't have an available insert state in
> > the clean up phase.  So the Assert in brininsertcleanup() is not
> always
> > right.  For example:
> >
> > regression=# update brin_summarize set value = brin_summarize.value;
> > server closed the connection unexpectedly
>
> I wasn't able to repro the issue on
> 86b64bafc19c4c60136a4038d2a8d1e6eecc59f2.
> with UPDATE/INSERT:
>
> This could be because since c5b7ba4e67aeb5d6f824b74f94114d99ed6e42b7,
> we have moved ExecOpenIndices()
> from ExecInitModifyTable() to ExecInsert(). Since we never open the
> indices if nothing is
> inserted, we would never attempt to close them with ExecCloseIndices()
> while the ii_AmCache
> is NULL (which is what causes this assertion failure).
>
>
> AFAICS we would also open the indices from ExecUpdate().  So if we
> update the table in a way that no new tuples are inserted, we will have
> this issue.  As I showed previously, the query below crashes for me on
> latest master (dc9f8a7983).
>
> regression=# update brin_summarize set value = brin_summarize.value;
> server closed the connection unexpectedly
>
> There are other code paths that call ExecOpenIndices(), such as
> ExecMerge(). I believe it's not hard to create queries that trigger
> this Assert for those cases.
>

FWIW I can readily reproduce it like this:

drop table t;
create table t (a int);
insert into t values (1);
create index on t using brin (a);
update t set a = a;

I however wonder if maybe we should do the check in index_insert_cleanup
and not in the AM callback. That seems simpler / better, because the AM
callbacks then can't make this mistake.

regards

--
Tomas Vondra
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