Re: WIP: Avoid creation of the free space map for small tables

From: John Naylor <jcnaylor(at)gmail(dot)com>
To: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WIP: Avoid creation of the free space map for small tables
Date: 2018-10-31 08:12:08
Message-ID: CAJVSVGVCyYWJqmWjkNZrW_i2=HhSCaeGq_BgxCnzuqxK7M=n7Q@mail.gmail.com
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Upthread I wrote:

> -A possible TODO item is to teach pg_upgrade not to link FSMs for
> small heaps. I haven't look into the feasibility of that, however.

This turned out to be relatively light weight (0002 attached). I had
to add relkind to the RelInfo struct and save the size of each heap as
its transferred. The attached SQL script will setup a couple test
cases to demonstrate pg_upgrade. Installations with large numbers of
small tables will be able to see space savings right away.

For 0001, I adjusted the README and docs, and also made some cosmetic
improvements to the code, mostly in the comments. I've set the
commitfest entry back to 'needs review'

One thing I noticed is that one behavior on master hasn't changed:
System catalogs created during bootstrap still have a FSM if they have
any data. Possibly related, catalogs also have a VM even if they have
no data at all. This isn't anything to get excited about, but it would
be nice to investigate, at least so it can be documented. A cursory
dig hasn't found the cause, but I'll keep doing that as time permits.

-John Naylor

Attachment Content-Type Size
v7-0001-Avoid-creation-of-the-free-space-map-for-small-ta.patch text/x-patch 29.3 KB
v7-0002-During-pg_upgrade-skip-transfer-of-FSMs-if-they-w.patch text/x-patch 7.4 KB
setup-fsm-pg_upgrade.sql application/sql 889 bytes

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