Subject: Re: get_relation_stats_hook()
From: Simon Riggs <simon@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Alvaro Herrera <alvherre@commandprompt.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
In-Reply-To: <16415.1214493494@sss.pgh.pa.us>
References: <1214490037.3845.136.camel@ebony.site>
	<16415.1214493494@sss.pgh.pa.us>
Content-Type: text/plain
Date: Thu, 26 Jun 2008 17:02:50 +0100
Message-Id: <1214496170.3845.196.camel@ebony.site>
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On Thu, 2008-06-26 at 11:18 -0400, Tom Lane wrote:
> Simon Riggs <simon@2ndquadrant.com> writes:
> > Currently we have a plugin capability for get_relation_info_hook(), but
> > no corresponding capability for statistics info.
> 
> > So, all calls to SearchSysCache would be replaced with a call to
> > get_relation_info_hook(), if present.
> 
> Surely you didn't mean ALL calls.  Please be more specific about what
> you're proposing.

The statistics relation STATRELATT is accessed in a few places in the
planner. Since it is in the syscache it is accessed directly from there.
I would like to add hooks so that stats data can come from somewhere
else other than the syscache for tables, just as we can already do with
get_relation_stats_hook(). These new changes would complete the existing
feature to ensure it is fully usabled in the way originally intended.

In selfunc.c: There are 3 calls to SearchSysCache(STATRELATT,...).

In lsyscache.c: There is 1 call to SearchSysCache(STATRELATT...) in
get_attavgwidth() and 2 calls to SysCacheGetAttr(STATRELATT...) in
get_attstatsslot().

Calls to SearchSysCache(STATRELATT...) would be replaced by a call to an
external module, if present, with a function pointer to
get_relation_stats_hook(). This returns a tuple with stats info about
that relation.

Calls to SysCacheGetAttr(STATRELATT...) would be replaced by a call to
an external module, if present with a function pointer to
get_attribute_stats_hook(). This returns a stats slot.

The call in ANALYZE would not be touched.

-- 
 Simon Riggs           www.2ndQuadrant.com
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