mirror/postgresql
2
0
Fork 0
mirror of https://git.postgresql.org/git/postgresql.git synced 2024-12-09 08:10:09 +08:00
Code Issues Packages Projects Releases Wiki Activity
e6e577490d
postgresql/doc/TODO.detail/exists
Bruce Momjian 1a712718ca Add IN/EXISTS file.
2002-01-20 05:12:57 +00:00

192 lines
9.6 KiB
Plaintext
Raw Blame History

From pgsql-sql-owner+M5999=candle.pha.pa.us=pgman@postgresql.org Mon Dec 17 01:39:56 2001
Return-path: <pgsql-sql-owner+M5999=candle.pha.pa.us=pgman@postgresql.org>
Received: from rs.postgresql.org (server1.pgsql.org [64.39.15.238] (may be forged))
by candle.pha.pa.us (8.11.6/8.10.1) with ESMTP id fBH6du410376
for <pgman@candle.pha.pa.us>; Mon, 17 Dec 2001 01:39:56 -0500 (EST)
Received: from postgresql.org (postgresql.org [64.49.215.8])
by rs.postgresql.org (8.11.6/8.11.6) with ESMTP id fBH6VoR80062
for <pgman@candle.pha.pa.us>; Mon, 17 Dec 2001 00:36:11 -0600 (CST)
(envelope-from pgsql-sql-owner+M5999=candle.pha.pa.us=pgman@postgresql.org)
Received: from sss.pgh.pa.us ([192.204.191.242])
by postgresql.org (8.11.3/8.11.4) with ESMTP id fBH6Lgm62418
for <pgsql-sql@postgresql.org>; Mon, 17 Dec 2001 01:21:42 -0500 (EST)
(envelope-from tgl@sss.pgh.pa.us)
Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1])
by sss.pgh.pa.us (8.11.4/8.11.4) with ESMTP id fBH6LHi29550;
Mon, 17 Dec 2001 01:21:17 -0500 (EST)
To: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
cc: "Stephan Szabo" <sszabo@megazone23.bigpanda.com>,
"MindTerm" <mindterm@yahoo.com>, pgsql-sql@postgresql.org
Subject: Re: [SQL] performance tuning in large function / transaction
In-Reply-To: <GNELIHDDFBOCMGBFGEFOIENDCAAA.chriskl@familyhealth.com.au>
References: <GNELIHDDFBOCMGBFGEFOIENDCAAA.chriskl@familyhealth.com.au>
Comments: In-reply-to "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
message dated "Mon, 17 Dec 2001 12:06:14 +0800"
Date: Mon, 17 Dec 2001 01:21:16 -0500
Message-ID: <29547.1008570076@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-sql-owner@postgresql.org
Status: OR
"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
> Is it true that the IN command is implemented sort of as a linked list
> linear time search? Is there any plan for a super-fast implementation of
> 'IN'?
This deserves a somewhat long-winded answer.
Postgres presently supports two kinds of IN (I'm not sure whether SQL92
allows any additional kinds):
1. Scalar-list IN: foo IN ('bar', 'baz', 'quux', ...)
2. Sub-select IN: foo IN (SELECT bar FROM ...)
In the scalar-list form, a variable is compared to an explicit list of
constants or expressions. This form is exactly equivalent to
foo = 'bar' OR foo = 'baz' OR foo = 'quux' OR ...
and is converted into that form by the parser. The planner is capable
of converting a WHERE clause of this kind into multiple passes of
indexscan, when foo is an indexed column and all the IN-list elements
are constants. Whether it actually will make that conversion depends
on the usual vagaries of pg_statistic entries, etc. But if it's a
unique or fairly-selective index, and there aren't a huge number of
entries in the IN list, a multiple indexscan should be a good plan.
In the sub-select form, we pretty much suck: for each tuple in the outer
query, we run the inner query until we find a matching value or the
inner query ends. This is basically a nested-loop scenario, with the
only (minimally) redeeming social value being that the planner realizes
it should pick a fast-start plan for the inner query. I think it should
be possible to convert this form into a modified kind of join (sort of
the reverse of an outer join: rather than at least one result per
lefthand row, at most one result per lefthand row), and then we could
use join methods that are more efficient than nested-loop. But no one's
tried to make that happen yet.
regards, tom lane
---------------------------(end of broadcast)---------------------------
TIP 2: you can get off all lists at once with the unregister command
(send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
From pgsql-sql-owner+M6000=candle.pha.pa.us=pgman@postgresql.org Mon Dec 17 01:49:56 2001
Return-path: <pgsql-sql-owner+M6000=candle.pha.pa.us=pgman@postgresql.org>
Received: from rs.postgresql.org (server1.pgsql.org [64.39.15.238] (may be forged))
by candle.pha.pa.us (8.11.6/8.10.1) with ESMTP id fBH6nu410869
for <pgman@candle.pha.pa.us>; Mon, 17 Dec 2001 01:49:56 -0500 (EST)
Received: from postgresql.org (postgresql.org [64.49.215.8])
by rs.postgresql.org (8.11.6/8.11.6) with ESMTP id fBH6fLR80303
for <pgman@candle.pha.pa.us>; Mon, 17 Dec 2001 00:45:51 -0600 (CST)
(envelope-from pgsql-sql-owner+M6000=candle.pha.pa.us=pgman@postgresql.org)
Received: from mail.iinet.net.au (symphony-05.iinet.net.au [203.59.3.37])
by postgresql.org (8.11.3/8.11.4) with SMTP id fBH6XFm62784
for <pgsql-sql@postgresql.org>; Mon, 17 Dec 2001 01:33:15 -0500 (EST)
(envelope-from chriskl@familyhealth.com.au)
Received: (qmail 30765 invoked by uid 666); 17 Dec 2001 06:33:10 -0000
Received: from unknown (HELO houston.familyhealth.com.au) (203.59.231.6)
by mail.iinet.net.au with SMTP; 17 Dec 2001 06:33:10 -0000
Received: (from root@localhost)
by houston.familyhealth.com.au (8.11.6/8.11.6) id fBH6XBH96532
for pgsql-sql@postgresql.org; Mon, 17 Dec 2001 14:33:11 +0800 (WST)
(envelope-from chriskl@familyhealth.com.au)
Received: from mariner (mariner.internal [192.168.0.101])
by houston.familyhealth.com.au (8.11.6/8.9.3) with SMTP id fBH6X7p96337;
Mon, 17 Dec 2001 14:33:07 +0800 (WST)
From: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
To: "Tom Lane" <tgl@sss.pgh.pa.us>
cc: "Stephan Szabo" <sszabo@megazone23.bigpanda.com>,
"MindTerm" <mindterm@yahoo.com>, <pgsql-sql@postgresql.org>
Subject: [SQL] 'IN' performance
Date: Mon, 17 Dec 2001 14:33:40 +0800
Message-ID: <GNELIHDDFBOCMGBFGEFOEENFCAAA.chriskl@familyhealth.com.au>
MIME-Version: 1.0
Content-Type: text/plain;
charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
X-Priority: 3 (Normal)
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook IMO, Build 9.0.2416 (9.0.2910.0)
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000
Importance: Normal
In-Reply-To: <29547.1008570076@sss.pgh.pa.us>
X-scanner: scanned by Inflex 0.1.5c - (http://www.inflex.co.za/)
Precedence: bulk
Sender: pgsql-sql-owner@postgresql.org
Status: OR
> In the sub-select form, we pretty much suck: for each tuple in the outer
> query, we run the inner query until we find a matching value or the
> inner query ends. This is basically a nested-loop scenario, with the
> only (minimally) redeeming social value being that the planner realizes
> it should pick a fast-start plan for the inner query. I think it should
> be possible to convert this form into a modified kind of join (sort of
> the reverse of an outer join: rather than at least one result per
> lefthand row, at most one result per lefthand row), and then we could
> use join methods that are more efficient than nested-loop. But no one's
> tried to make that happen yet.
That's what I was thinking...where abouts does all that activity happen?
I assume the planner knows that it doesn't have to reevaluate the subquery
if it's not correlated?
Chris
---------------------------(end of broadcast)---------------------------
TIP 2: you can get off all lists at once with the unregister command
(send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
From pgsql-sql-owner+M6001=candle.pha.pa.us=pgman@postgresql.org Mon Dec 17 02:00:10 2001
Return-path: <pgsql-sql-owner+M6001=candle.pha.pa.us=pgman@postgresql.org>
Received: from rs.postgresql.org (server1.pgsql.org [64.39.15.238] (may be forged))
by candle.pha.pa.us (8.11.6/8.10.1) with ESMTP id fBH709411405
for <pgman@candle.pha.pa.us>; Mon, 17 Dec 2001 02:00:09 -0500 (EST)
Received: from postgresql.org (postgresql.org [64.49.215.8])
by rs.postgresql.org (8.11.6/8.11.6) with ESMTP id fBH6psR80624
for <pgman@candle.pha.pa.us>; Mon, 17 Dec 2001 00:56:15 -0600 (CST)
(envelope-from pgsql-sql-owner+M6001=candle.pha.pa.us=pgman@postgresql.org)
Received: from sss.pgh.pa.us ([192.204.191.242])
by postgresql.org (8.11.3/8.11.4) with ESMTP id fBH6iCm63171
for <pgsql-sql@postgresql.org>; Mon, 17 Dec 2001 01:44:12 -0500 (EST)
(envelope-from tgl@sss.pgh.pa.us)
Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1])
by sss.pgh.pa.us (8.11.4/8.11.4) with ESMTP id fBH6i3i29733;
Mon, 17 Dec 2001 01:44:03 -0500 (EST)
To: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
cc: "Stephan Szabo" <sszabo@megazone23.bigpanda.com>,
"MindTerm" <mindterm@yahoo.com>, pgsql-sql@postgresql.org
Subject: Re: [SQL] 'IN' performance
In-Reply-To: <GNELIHDDFBOCMGBFGEFOEENFCAAA.chriskl@familyhealth.com.au>
References: <GNELIHDDFBOCMGBFGEFOEENFCAAA.chriskl@familyhealth.com.au>
Comments: In-reply-to "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
message dated "Mon, 17 Dec 2001 14:33:40 +0800"
Date: Mon, 17 Dec 2001 01:44:03 -0500
Message-ID: <29730.1008571443@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-sql-owner@postgresql.org
Status: OR
"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
> That's what I was thinking...where abouts does all that activity happen?
The infrastructure for different join rules already exists. There'd
need to be a new JOIN_xxx type added to the various join nodes in the
executor, but AFAICS that's just a minor extension. The part that is
perhaps not trivial is in the planner. All the existing inner and outer
join types start out expressed as joins in the original query. To make
IN into a join, the planner would have to hoist up a clause from WHERE
into the join-tree structure. I think it can be done, but I have not
thought hard about where and how, nor about what semantic restrictions
might need to be checked.
regards, tom lane
---------------------------(end of broadcast)---------------------------
TIP 2: you can get off all lists at once with the unregister command
(send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
Reference in New Issue View Git Blame Copy Permalink