Re: Freeze avoidance of very large table.

From: Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Peter Geoghegan <pg(at)heroku(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Petr Jelinek <petr(at)2ndquadrant(dot)com>, Greg S <stark(at)mit(dot)edu>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Freeze avoidance of very large table.
Date: 2016-03-02 23:57:27
Message-ID: 56D77DE7.7080309@BlueTreble.com
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On 3/2/16 5:41 PM, Tom Lane wrote:
> Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com> writes:
>> On 3/2/16 4:21 PM, Peter Geoghegan wrote:
>>> I think you should commit this. The chances of anyone other than you
>>> and Masahiko recalling that you developed this tool in 3 years is
>>> essentially nil. I think that the cost of committing a developer-level
>>> debugging tool like this is very low. Modules like pg_freespacemap
>>> currently already have no chance of being of use to ordinary users.
>>> All you need to do is restrict the functions to throw an error when
>>> called by non-superusers, out of caution.
>>>
>>> It's a problem that modules like pg_stat_statements and
>>> pg_freespacemap are currently lumped together in the documentation,
>>> but we all know that.
>
>> +1.
>
> Would it make any sense to stick it under src/test/modules/ instead of
> contrib/ ? That would help make it clear that it's a debugging tool
> and not something we expect end users to use.

I haven't looked at it in detail; is there something inherently
dangerous about it?

When I'm forced to wear a DBA hat, I'd really love to be able to find
out what VM status for a large table is. If it's in contrib they'll know
the tool is there; if it's under src then there's about 0 chance of
that. I'd think SU-only and any appropriate warnings would be enough
heads-up for DBAs to be careful with it.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com

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