Re: Tid scan improvements

From: Andres Freund <andres(at)anarazel(dot)de>
To: Edmund Horner <ejrh00(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Tid scan improvements
Date: 2019-03-26 16:35:33
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On 2019-03-26 19:11:13 +1300, Edmund Horner wrote:
> The changes in heapam.c were required for backward scan support, as
> used by ORDER BY ctid DESC and MAX(ctid); and also for FETCH LAST and
> FETCH PRIOR. I have removed the backward scans functionality from the
> current set of patches, but support for backward cursor fetches
> remains.
> I guess to brutally simplify the patch further, we could give up
> backward cursor fetches entirely? This means such cursors that end up
> using a TidRangeScan will require SCROLL to go backwards (which is a
> small pain for user experience), but TBH I don't think backwards-going
> cursors on CTID will be hugely common.

FWIW, I think it'd be entirely reasonable to remove support for backward
scans without SCROLL. In fact, I think it'd be wasted effort to maintain
code for it, without a pretty clear reason why we need it (unless it
were trivial to support, which it isn't).


Andres Freund

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