Horton

Re: reloption to prevent VACUUM from truncating empty pages at the end of relation

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

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Andres Freund <andres@anarazel.de>
Cc: Michael Paquier <michael@paquier.xyz>, Amit Kapila <amit.kapila16@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Fujii Masao <masao.fujii@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-04-19T20:38:02Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Add TRUNCATE parameter to VACUUM.

  2. Add vacuum_truncate reloption.

  3. Allow VACUUM to be run with index cleanup disabled.

Andres Freund wrote:
> On 2018-04-19 16:56:59 -0300, Alvaro Herrera wrote:
> > Michael Paquier wrote:
> > 
> > > Then, let's consider the beginning of the first commit fest of v12 as
> > > judgement.  Implementing radix tree for shared buffers is a long-term
> > > project, which has no guarantee to get merged, while a visibly-simple
> > > reloptions which helps in some cases...
> > 
> > In the scenario we studied, the truncations were causing periodic
> > hiccups which were quite severe.
> 
> Was that with the current logic of breaking the truncations into smaller
> chunks?

Yes -- it was with 9.5.7.  I was skeptical about that stuff working
correctly for a toast table, BTW, but I didn't manage to prove anything.

> > The truncations were completely useless anyway because the table
> > grew back to the original size daily (a few dozen GBs I think).
> > That was a lot of unnecessary work, and under exclusive lock no
> > less.
> 
> FWIW, One goal of the different buffer mapping implementation is to also
> make both increasing and decreasing size of relations possible without
> an AEL.

Oh, that sounds very useful.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
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