Re: [HACKERS] Patch: Write Amplification Reduction Method (WARM)

> @@ -234,6 +236,21 @@ index_beginscan(Relation heapRelation,
>       scan->heapRelation = heapRelation;
>       scan->xs_snapshot = snapshot;
>
> +     /*
> +      * If the index supports recheck, make sure that index tuple is saved
> +      * during index scans.
> +      *
> +      * XXX Ideally, we should look at all indexes on the table and check if
> +      * WARM is at all supported on the base table. If WARM is not supported
> +      * then we don't need to do any recheck. RelationGetIndexAttrBitmap() does
> +      * do that and sets rd_supportswarm after looking at all indexes. But we
> +      * don't know if the function was called earlier in the session when we're
> +      * here. We can't call it now because there exists a risk of causing
> +      * deadlock.
> +      */
> +     if (indexRelation->rd_amroutine->amrecheck)
> +             scan->xs_want_itup = true;
> +
>       return scan;
>  }

I didn't like this comment very much.  But it's not necessary: you have
already given relcache responsibility for setting rd_supportswarm.  The
only problem seems to be that you set it in RelationGetIndexAttrBitmap
instead of RelationGetIndexList, but it's not clear to me why.  I think
if the latter function is in charge, then we can trust the flag more
than the current situation.