| From: | Michael Paquier <michael(at)paquier(dot)xyz> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>, Robert Haas <robertmhaas(at)gmail(dot)com> |
| Subject: | Re: Move pg_attribute.attcompression to earlier in struct for reduced size? |
| Date: | 2021-05-27 02:07:53 |
| Message-ID: | YK7++YoPYbsHOb+W@paquier.xyz |
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| Lists: | pgsql-hackers |
On Wed, May 26, 2021 at 06:54:15PM -0700, Andres Freund wrote:
> Oh, it'll definitely be more expensive in that case - but that seems
> fair game. What I was wondering about was whether VACUUM FULL would be
> measurably slower, because we'll now call toast_get_compression_id() on
> each varlena datum. It's pretty easy for VACUUM FULL to be CPU bound
> already, and presumably this'll add a bit.
This depends on the number of attributes, but I do see an extra 0.5%
__memmove_avx_unaligned_erms in reform_and_rewrite_tuple() for a
normal VACUUM FULL with a 1-int-column relation on a perf profile,
with rewrite_heap_tuple eating most of it as in the past, so that's
within the noise bandwidth if you measure the runtime. What would be
the worst case here, a table with one text column made of non-NULL
still very short values?
--
Michael
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