Re: patch : Allow toast tables to be moved to a different tablespace

Jim Nasby <jim.nasby@bluetreble.com>

From: Jim Nasby <Jim.Nasby@BlueTreble.com>

To: Andres Freund <andres@anarazel.de>, Tom Lane <tgl@sss.pgh.pa.us>

Cc: Andreas Karlsson <andreas@proxel.se>, Julien Tachoires <julmon@gmail.com>, Alex Shulgin <ash@commandprompt.com>, Alvaro Herrera <alvherre@2ndquadrant.com>, Jaime Casanova <jaime@2ndquadrant.com>, Robert Haas <robertmhaas@gmail.com>, Pg Hackers <pgsql-hackers@postgresql.org>

Date: 2015-07-14T21:57:34Z

Lists: pgsql-hackers

On 7/7/15 7:07 AM, Andres Freund wrote:
> On 2015-07-03 18:03:58 -0400, Tom Lane wrote:
>> I have just looked through this thread, and TBH I think we should reject
>> this patch altogether --- not RWF, but "no we don't want this".  The
>> use-case remains hypothetical: no performance numbers showing a real-world
>> benefit have been exhibited AFAICS.
>
> It's not that hard to imagine a performance benefit though? If the
> toasted column is accessed infrequently/just after filtering on other
> columns (not uncommon) it could very well be beneficial to put the main
> table on fast storage (SSD) and the toast table on slow storage
> (spinning rust).
>
> I've seen humoungous toast tables that are barely ever read for tables
> that are constantly a couple times in the field.

+1. I know of one case where the heap was ~8GB and TOAST was over 400GB.
-- 
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Data in Trouble? Get it in Treble! http://BlueTreble.com