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Re: TOAST versus VACUUM, or "missing chunk number 0 for toast value" identified

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Andrew Hammond <andrew(dot)george(dot)hammond(at)gmail(dot)com>
Subject: Re: TOAST versus VACUUM, or "missing chunk number 0 for toast value" identified
Date: 2011-10-28 19:47:13
Message-ID: 1319831114-sup-3152@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-hackers
Excerpts from Tom Lane's message of vie oct 28 15:37:43 -0300 2011:

> The main concern I had about detoast before caching is the risk of
> circularity, ie, needing detoastable cache entries in order to figure
> out how to detoast.  But I think it's probably okay.  The current list
> of catalogs with toast tables is
> 
>  pg_attrdef
>  pg_constraint
>  pg_database
>  pg_db_role_setting
>  pg_description
>  pg_proc
>  pg_rewrite
>  pg_seclabel
>  pg_shdescription
>  pg_statistic
>  pg_trigger
> 
> Of these, only pg_proc is even conceivably consulted during a toast
> table fetch, and we can be sure that functions needed for such a fetch
> don't have toasted entries.  But we will have to be very wary of any
> future proposal for adding a toast table to pg_class, pg_index, etc.

BTW we had previous discussions about dropping pg_database's toast
table.  Maybe this is a good time to do it, even if there's no risk of
this bug (or the hypothetical circularity detoasting problem) showing up
there.

-- 
Álvaro Herrera <alvherre(at)commandprompt(dot)com>
The PostgreSQL Company - Command Prompt, Inc.
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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