Re: Use of additional index columns in rows filtering

On 7/19/23 19:17, Jeff Davis wrote:
> On Wed, 2023-07-19 at 11:16 +0200, Tomas Vondra wrote:
>> I wonder if Andres was right (in the index prefetch thread) that
>> splitting regular index scans and index-only scans may not be ideal.
>> In
>> a way, this patch moves those nodes closer, both in capability and
>> code
>> (because now both use index_getnext_tid etc.).
>
> Yeah. I could also imagine decomposing the index scan node into more
> pieces, but I don't think it would work out to be a clean data flow.
> Either way, probably out of scope for this patch.
>

OK

> For this patch I think we should just tweak the EXPLAIN output so that
> it's a little more clear what parts are index-only (at least if VM bit
> is set) and what parts need to go to the heap.
>

Makes sense, I also need to think about maybe not having duplicate
clauses in the two lists. What annoys me on that it partially prevents
the cost-based reordering done by order_qual_clauses(). So maybe we
should have three lists ... Also, some of the expressions count be
fairly expensive.

BTW could you double-check how I expanded the index_getnext_slot()? I
recall I wasn't entirely confident the result is correct, and I wanted
to try getting rid of the "while (true)" loop.

regards

--
Tomas Vondra
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