Horton

Re: Move pg_attribute.attcompression to earlier in struct for reduced size?

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Michael Paquier <michael@paquier.xyz>, Dilip Kumar <dilipbalaut@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>, Robert Haas <robertmhaas@gmail.com>
Date: 2021-05-27T01:54:15Z
Lists: pgsql-hackers 
Hi,

On 2021-05-26 20:35:46 -0400, Tom Lane wrote:
> Andres Freund <andres@anarazel.de> writes:
> > The efficiency bit is probably going to be swamped by the addition of
> > the compression handling, given the amount of additional work we're now
> > doing in in reform_and_rewrite_tuple().
> 
> Only if the user has explicitly requested a change of compression, no?

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.

Greetings,

Andres Freund

Commits

  1. Remove forced toast recompression in VACUUM FULL/CLUSTER

  2. Rethink definition of pg_attribute.attcompression.

  3. Fix memory leak when de-toasting compressed values in VACUUM FULL/CLUSTER

  4. Re-order pg_attribute columns to eliminate some padding space.

  5. Add more TAP tests for pg_dump with attribute compression