| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Cc: | Amit Langote <amitlangote09(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: making update/delete of inheritance trees scale better |
| Date: | 2020-10-30 21:10:17 |
| Message-ID: | 136943.1604092217@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Heikki Linnakangas <hlinnaka(at)iki(dot)fi> writes:
> I also did some quick performance testing with a simple update designed
> as a worst-case scenario:
> vacuum tab; update tab set b = b, a = a;
> In this case, the patch fetches the old tuple, but it wouldn't really
> need to, because all the columns are updated. Could we optimize that
> special case?
I'm not following. We need to read the old values of a and b for
the update source expressions, no?
(One could imagine realizing that this is a no-op update, but that
seems quite distinct from the problem at hand, and probably not
worth the cycles.)
regards, tom lane
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