public inbox for [email protected]  

help / color / mirror / Atom feed

From: PFC <[email protected]>
To: Tom Lane <[email protected]>
To: Greg Smith <[email protected]>
Cc: [email protected]
Subject: Re: Volunteer to build a configuration tool
Date: Wed, 20 Jun 2007 09:49:02 +0200
Message-ID: <op.tt7mn0m9cigqcu@apollo13> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>


> To me, the worst catch-22 we face in this area is that we'd like the
> optimizer's choices of plan to be stable and understandable, but the
> real-world costs of queries depend enormously on short-term conditions
> such as how much of the table has been sucked into RAM recently by
> other queries.  I have no good answer to that one.

	Yeah, there is currently no way to tell the optimizer things like :

	- this table/portion of a table is not frequently accessed, so it won't  
be in the cache, so please use low-seek plans (like bitmap index scan)
	- this table/portion of a table is used all the time so high-seek-count  
plans can be used like index scan or nested loops since everything is in  
RAM

	Except planner hints (argh) I see no way to give this information to the  
machine... since it's mostly in the mind of the DBA. Maybe a per-table  
"cache temperature" param (hot, warm, cold), but what about the log table,  
the end of which is cached, but not the old records ? It's messy.

	Still PG does a pretty excellent job most of the time.

view thread (33+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected], [email protected], [email protected], [email protected]
  Subject: Re: Volunteer to build a configuration tool
  In-Reply-To: <op.tt7mn0m9cigqcu@apollo13>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox