Re: A few new options for vacuumdb

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: "Bossart, Nathan" <bossartn(at)amazon(dot)com>
Cc: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: A few new options for vacuumdb
Date: 2019-01-09 01:06:37
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On Tue, Jan 08, 2019 at 06:46:11PM +0000, Bossart, Nathan wrote:
> This was done in order to maintain the current behavior that
> appendQualifiedRelation() gives us. I found that skipping the
> search_path handling here forced us to specify the schema in the
> argument for --table in most cases. At the very least, I could add a
> comment here to highlight the importance of fully qualifying
> everything in the catalog query. What do you think?

A comment sounds like a good thing. And we really shouldn't hijack
search_path even for one query...

> Looks good to me, except for one small thing in the documentation:
> + <para>
> + Disable all page-skipping behavior during processing based on
> + the visibility map, similarly to the option
> + <literal>DISABLE_PAGE_SKIPPING</literal> for <command>VACUUM</command>.
> + </para>
> I think the "similarly to the option" part is slightly misleading.
> It's not just similar, it _is_ using that option in the generated
> commands. Perhaps we could point to the VACUUM documentation for more
> information about this one.

Sure. If you have any suggestions, please feel free. Adding a link
to VACUUM documentation sounds good to me, as long as we avoid
duplicating the description related to DISABLE_PAGE_SKIPPING on the
VACUUM page.

> Good point. I think allowing multiple different relation size options
> here would be confusing, too (e.g. --min-relation-size versus
> --min-total-relation-size). IMO pg_total_relation_size() is the way
> to go here, as we'll most likely need to process the indexes and TOAST
> tables, too. If/when there is a DISABLE_INDEX_CLEANUP option for
> VACUUM, we'd then want to use pg_table_size() when --min-relation-size
> and --disable-index-cleanup are used together in vacuumdb.
> Thoughts?

Yes, using pg_total_relation_size() looks like the best option to me
here as well, still this does not make me 100% comfortable from the
user perspective.

> I've realized that I forgot to add links to the XID/MXID wraparound
> documentation like you suggested a while back. I'll make sure that
> gets included in the next patch set, too.

Nice, thanks.

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