From: Michael Paquier <michael@paquier.xyz>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Move pg_attribute.attcompression to earlier in struct for reduced size?
Date: Wed, 9 Jun 2021 12:24:57 +0900
Message-ID: <YMA0iRYL49kdCCZu@paquier.xyz> (raw)
In-Reply-To: <202106081439.m2pwwk5yvcrd@alvherre.pgsql>
References: <YLw797TlZxbB0QHU@paquier.xyz>
<202106081439.m2pwwk5yvcrd@alvherre.pgsql>
On Tue, Jun 08, 2021 at 10:39:24AM -0400, Alvaro Herrera wrote:
> My unverified guess is that this code causes too many pipeline stalls
> while executing the big per-column loop. Maybe it would be better to
> scan the attribute array twice: one to collect all data from
> Form_pg_attribute for each column into nicely packed arrays, then in a
> second loop process all the recompressions together ... the idea being
> that the first loop can run without stalling.
You mean for attlen and attcompression, right? I agree that it would
help.
A extra set of things worth it here would be to move the allocation
and memset(0) of values_free from reform_and_rewrite_tuple(), and do
the round of pfree() calls if at least one value has been detoasted.
> Maybe at this point reverting is the only solution.
That's a safe bet at this point. It would be good to conclude this
one by beta2 IMO.
--
Michael
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To: pgsql-hackers@postgresql.org
Cc: michael@paquier.xyz, alvherre@alvh.no-ip.org, tgl@sss.pgh.pa.us, robertmhaas@gmail.com, dilipbalaut@gmail.com, andres@anarazel.de
Subject: Re: Move pg_attribute.attcompression to earlier in struct for reduced size?
In-Reply-To: <YMA0iRYL49kdCCZu@paquier.xyz>
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