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Re: get_relation_stats_hook()

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: get_relation_stats_hook()
Date: 2008-06-26 16:02:50
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackerspgsql-patches
On Thu, 2008-06-26 at 11:18 -0400, Tom Lane wrote:
> Simon Riggs <simon(at)2ndquadrant(dot)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

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 
 PostgreSQL Training, Services and Support

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