Skip site navigation (1) Skip section navigation (2)

Re: Access to Row ID information in Functions

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Paul Ramsey" <pramsey(at)cleverelephant(dot)ca>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Access to Row ID information in Functions
Date: 2008-04-01 21:37:43
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
"Paul Ramsey" <pramsey(at)cleverelephant(dot)ca> writes:
> The "optimized" form gets cached and retrieved from a memory context.
> Each time the function is run within a statement it checks the cache,
> and sees if one of its arguments are the same as the last time around.
> If so, it uses the prepared version of that argument. If not, it
> builds a new prepared version and caches that.

> The key here is being able to check the identify of the arguments...
> is this argument A the same as the one we processed last time? One way
> is to do a memcmp.  But it seems likely that PgSQL knows exactly
> whether it is running a nested loop, or a literal, and could tell
> somehow that argument A is the same with each call.

Not really.  Certainly there's no way that that information would
propagate into function calls.

In the special case where your argument is a literal constant, I think
there is enough information available to detect that that's the case
(look at get_fn_expr_argtype).  But if it's not, there's no very good
way to know whether it's the same as last time.

Perhaps it would be worth changing your on-disk storage format to allow
cheaper checking?  For instance include a hash value.

			regards, tom lane

In response to


pgsql-hackers by date

Next:From: Paul RamseyDate: 2008-04-01 22:08:17
Subject: Re: Access to Row ID information in Functions
Previous:From: Murray CummingDate: 2008-04-01 21:31:23
Subject: Re: [HACKERS] Avahi support for Postgresql

Privacy Policy | About PostgreSQL
Copyright © 1996-2018 The PostgreSQL Global Development Group