Horton

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

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Michael Paquier <michael@paquier.xyz>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-06-03T16:04:48Z
Lists: pgsql-hackers 
On 2021-Jun-02, Michael Paquier wrote:

> After 12 runs of VACUUM FULL on my laptop, I have removed the two
> highest and the two lowest to remove some noise, and did an average of
> the rest:
> - HEAD, 100 text columns: 5720ms
> - REL_13_STABLE, 100 text columns: 4308ms
> - HEAD, 200 text columns: 10020ms
> - REL_13_STABLE, 200 text columns:  8319ms
> 
> So yes, that looks much visible to me, and an argument in favor of the
> removal of the forced recompression on HEAD when rewriting tuples.

Just to be clear -- that's the time to vacuum the table without changing
the compression algorithm, right?  So the overhead is just the check for
whether the recompression is needed, not the recompression itself?

If the check for recompression is this expensive, then yeah I agree that
we should take it out.  If recompression is actually occurring, then I
don't think this is a good test :-)

-- 
Álvaro Herrera       Valdivia, Chile

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