Horton

Re: [Patch] Optimize dropping of relation buffers using dlist

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: "tsunakawa.takay@fujitsu.com" <tsunakawa.takay@fujitsu.com>
Cc: "k.jamison@fujitsu.com" <k.jamison@fujitsu.com>, Kyotaro Horiguchi <horikyota.ntt@gmail.com>, Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>, Thomas Munro <thomas.munro@gmail.com>, Robert Haas <robertmhaas@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2020-12-08T10:58:41Z
Lists: pgsql-hackers 
On Tue, Dec 8, 2020 at 12:13 PM tsunakawa.takay@fujitsu.com
<tsunakawa.takay@fujitsu.com> wrote:
>
> From: Jamison, Kirk/ジャミソン カーク <k.jamison@fujitsu.com>
> > Because one of the rel's cached value was false, it forced the
> > full-scan path for TRUNCATE.
> > Is there a possible workaround for this?
>
> Hmm, the other two relfilenodes are for the TOAST table and index of the target table.  I think the INSERT didn't access those TOAST relfilenodes because the inserted data was stored in the main storage.  But TRUNCATE always truncates all the three relfilenodes.  So, the standby had not opened the relfilenode for the TOAST stuff or cached its size when replaying the TRUNCATE.
>
> I'm afraid this is more common than we can ignore and accept the slow traditional path, but I don't think of a good idea to use the cached flag.
>

I also can't think of a way to use an optimized path for such cases
but I don't agree with your comment on if it is common enough that we
leave this optimization entirely for the truncate path.

-- 
With Regards,
Amit Kapila.

Commits

  1. Fix size overflow in calculation introduced by commits d6ad34f3 and bea449c6.

  2. Optimize DropRelFileNodesAllBuffers() for recovery.

  3. Optimize DropRelFileNodeBuffers() for recovery.

  4. Cache smgrnblocks() results in recovery.

  5. Add a check to prevent overwriting valid data if smgrnblocks() gives a