Re: Fix Brin Private Spool Initialization (src/backend/access/brin/brin.c)

On 12/26/23 19:10, Ranier Vilela wrote:
> Hi,
>
> The commit b437571 <http://b437571714707bc6466abde1a0af5e69aaade09c> I
> think has an oversight.
> When allocate memory and initialize private spool in function:
> _brin_leader_participate_as_worker
>
> The behavior is the bs_spool (heap and index fields)
> are left empty.
>
> The code affected is:
>   buildstate->bs_spool = (BrinSpool *) palloc0(sizeof(BrinSpool));
> - buildstate->bs_spool->heap = buildstate->bs_spool->heap;
> - buildstate->bs_spool->index = buildstate->bs_spool->index;
> + buildstate->bs_spool->heap = heap;
> + buildstate->bs_spool->index = index;
>
> Is the fix correct?
>

Thanks for noticing this. Yes, I believe this is a bug - the assignments
are certainly wrong, it leaves the fields set to NULL.

I wonder how come this didn't fail during testing. Surely, if the leader
participates as a worker, the tuplesort_begin_index_brin shall be called
with heap/index being NULL, leading to some failure during the sort. But
maybe this means we don't actually need the heap/index fields, it's just
a copy of TuplesortIndexArg, but BRIN does not need that because we sort
the tuples by blkno, and we don't need the descriptors for that.

In any case, the _brin_parallel_scan_and_build does not actually need
the separate heap/index arguments, those are already in the spool.

I'll try to figure out if we want to simplify the tuplesort or remove
the arguments from _brin_parallel_scan_and_build.

regards

--
Tomas Vondra
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