Date: Fri, 4 Sep 2020 14:46:19 +0200
From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Kasahara Tatsuhito <kasahara.tatsuhito@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, torikoshia <torikoshia@oss.nttdata.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Get memory contexts of an arbitrary backend process
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On Fri, Sep 04, 2020 at 11:47:30AM +0900, Kasahara Tatsuhito wrote:
>On Fri, Sep 4, 2020 at 2:40 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Kasahara Tatsuhito <kasahara.tatsuhito@gmail.com> writes:
>> > Yes, but it's not only for future expansion, but also for the
>> > usability and the stability of this feature.
>> > For example, if you want to read one dumped file multiple times and analyze it,
>> > you will want the ability to just read the dump.
>>
>> If we design it to make that possible, how are we going to prevent disk
>> space leaks from never-cleaned-up dump files?
>In my thought, with features such as a view that allows us to see a
>list of dumped files,
>it would be better to have a function that simply deletes the dump
>files associated with a specific PID,
>or to delete all dump files.
>Some files may be dumped with unexpected delays, so I think the
>cleaning feature will be necessary.
>( Also, as the pgsql_tmp file, it might better to delete dump files
>when PostgreSQL start.)
>
>Or should we try to delete the dump file as soon as we can read it?
>

IMO making the cleanup a responsibility of the users (e.g. by exposing
the list of dumped files through a view and expecting users to delete
them in some way) is rather fragile.

I don't quite see what's the point of designing it this way. It was
suggested this improves stability and usability of this feature, but
surely making it unnecessarily complex contradicts both points?

IMHO if the user needs to process the dump repeatedly, what's preventing
him/her from storing it in a file, or something like that? At that point
it's clear it's up to them to remove the file. So I suggest to keep the
feature as simple as possible - hand the dump over and delete.


regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services