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

From: John Naylor <john(dot)naylor(at)2ndquadrant(dot)com>
To: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Cc: Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com>, Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WIP: Avoid creation of the free space map for small tables
Date: 2019-01-30 14:41:46
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On Wed, Jan 30, 2019 at 2:11 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> This is much better than the earlier version of test and there is no
> dependency on the vacuum. However, I feel still there is some
> dependency on how the rows will fit in a page and we have seen some
> related failures due to alignment stuff. By looking at the test, I
> can't envision any such problem, but how about if we just write some
> simple tests where we can check that the FSM won't be created for very
> small number of records say one or two and then when we increase the
> records FSM gets created, here if we want, we can even use vacuum to
> ensure FSM gets created. Once we are sure that the main patch passes
> all the buildfarm tests, we can extend the test to something advanced
> as you are proposing now. I think that will reduce the chances of
> failure, what do you think?

That's probably a good idea to limit risk. I just very basic tests
now, and vacuum before every relation size check to make sure any FSM
extension (whether desired or not) is invoked. Also, in my last patch
I forgot to implement explicit checks of the block number instead of
assuming how many rows will fit on a page. I've used a plpgsql code
block to do this.

John Naylor
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Attachment Content-Type Size
simple-regression-test-plus-ctid-loop.patch text/x-patch 4.8 KB

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