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1698 lines
72 KiB
Plaintext
From owner-pgsql-hackers@hub.org Wed Nov 18 14:40:49 1998
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id m0zgDnj-000EBTC; Wed, 18 Nov 98 21:02 MET
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Message-Id: <m0zgDnj-000EBTC@orion.SAPserv.Hamburg.dsh.de>
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From: jwieck@debis.com (Jan Wieck)
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Subject: Re: [HACKERS] PREPARE
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To: meskes@usa.net (Michael Meskes)
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Date: Wed, 18 Nov 1998 21:02:06 +0100 (MET)
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Cc: pgsql-hackers@hub.org
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Reply-To: jwieck@debis.com (Jan Wieck)
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In-Reply-To: <19981118084843.B869@usa.net> from "Michael Meskes" at Nov 18, 98 08:48:43 am
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X-Mailer: ELM [version 2.4 PL25]
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Content-Type: text
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Sender: owner-pgsql-hackers@postgreSQL.org
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Precedence: bulk
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Status: RO
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Michael Meskes wrote:
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>
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> On Wed, Nov 18, 1998 at 03:23:30AM +0000, Thomas G. Lockhart wrote:
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> > > I didn't get this one completly. What input do you mean?
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> >
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> > Just the original string/query to be prepared...
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>
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> I see. But wouldn't it be more useful to preprocess the query and store the
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> resulting nodes instead? We don't want to parse the statement everytime a
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> variable binding comes in.
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Right. A real improvement would only be to have the prepared
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execution plan in the backend and just giving the parameter
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values.
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I can think of the following construct:
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PREPARE optimizable-statement;
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That one will run parser/rewrite/planner, create a new memory
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context with a unique identifier and saves the querytree's
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and plan's in it. Parameter values are identified by the
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usual $n notation. The command returns the identifier.
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EXECUTE QUERY identifier [value [, ...]];
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then get's back the prepared plan and querytree by the id,
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creates an executor context with the given values in the
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parameter array and calls ExecutorRun() for them.
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The PREPARE needs to analyze the resulting parsetrees to get
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the datatypes (and maybe atttypmod's) of the parameters, so
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EXECUTE QUERY can convert the values into Datum's using the
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types input functions. And the EXECUTE has to be handled
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special in tcop (it's something between a regular query and
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an utility statement). But it's not too hard to implement.
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Finally a
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FORGET QUERY identifier;
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(don't remember how the others named it) will remove the
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prepared plan etc. simply by destroying the memory context
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and dropping the identifier from the id->mcontext+prepareinfo
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mapping.
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This all restricts the usage of PREPARE to optimizable
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statements. Is it required to be able to prepare utility
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statements (like CREATE TABLE or so) too?
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Jan
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--
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#======================================================================#
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# It's easier to get forgiveness for being wrong than for being right. #
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# Let's break this rule - forgive me. #
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#======================================== jwieck@debis.com (Jan Wieck) #
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From pgsql-hackers-owner+M67@postgresql.org Tue Oct 31 19:18:16 2000
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Received: from mail.postgresql.org ([216.126.85.28])
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(envelope-from pgsql-hackers-owner+M67@postgresql.org)
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Received: from ara.zf.jcu.cz (ara.zf.jcu.cz [160.217.161.4])
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for <pgsql-hackers@postgresql.org>; Tue, 31 Oct 2000 19:17:08 -0500 (EST)
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(envelope-from zakkr@zf.jcu.cz)
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Wed, 1 Nov 2000 01:16:42 +0100
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Date: Wed, 1 Nov 2000 01:16:42 +0100 (CET)
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From: Karel Zak <zakkr@zf.jcu.cz>
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To: Alfred Perlstein <bright@wintelcom.net>
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cc: pgsql-hackers@postgresql.org
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Subject: Re: [HACKERS] Query cache import?
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In-Reply-To: <20001031151144.F22110@fw.wintelcom.net>
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Message-ID: <Pine.LNX.3.96.1001101005110.31713B-100000@ara.zf.jcu.cz>
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MIME-Version: 1.0
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Sender: pgsql-hackers-owner@postgresql.org
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Status: OR
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On Tue, 31 Oct 2000, Alfred Perlstein wrote:
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> I never saw much traffic regarding Karel's work on making stored
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> proceedures:
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>
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> http://people.freebsd.org/~alfred/karel-pgsql.txt
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>
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> What happened with this? It looked pretty interesting. :(
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It's probably a little about me :-) ... well,
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My query cache is in usable state and it's efficient for all
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things those motivate me to work on this.
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some basic features:
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- share parsed plans between backends in shared memory
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- store plans to private backend hash table
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- use parameters for stored queries
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- better design for SPI
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- memory usage for saved plans
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- save plans "by key"
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The current query cache code depend on 7.1 memory management. After
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official 7.1 release I prepare patch with query cache+SPI (if not
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hit me over head, please ..)
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All what will doing next time not depend on me, *it's on code developers*.
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For example Jan has interesting idea about caching all plans which
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processing backend. But it's far future and IMHO we must go by small
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steps to Oracle's funeral :-)
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If I need the query cache in the my work (typical for some web+pgsql) or
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will some public interest I will continue on this, if not I freeze it.
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(Exists more interesting work like http://mape.jcu.cz ... sorry of
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advertising :-)
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Karel
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From pgsql-hackers-owner+M312@postgresql.org Mon Nov 6 03:27:32 2000
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Received: from mail.postgresql.org (webmail.postgresql.org [216.126.85.28])
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for <pgsql-hackers@postgresql.org>; Mon, 6 Nov 2000 03:15:40 -0500 (EST)
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Mon, 6 Nov 2000 09:15:04 +0100
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Date: Mon, 6 Nov 2000 09:15:04 +0100 (CET)
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From: Karel Zak <zakkr@zf.jcu.cz>
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To: Christof Petig <christof.petig@wtal.de>
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cc: Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>,
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The Hermit Hacker <scrappy@hub.org>, pgsql-hackers@postgresql.org
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Subject: Re: AW: [HACKERS] Re: [GENERAL] Query caching
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In-Reply-To: <3A02DDFF.E8CBFCF3@wtal.de>
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Message-ID: <Pine.LNX.3.96.1001106090801.20612C-100000@ara.zf.jcu.cz>
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MIME-Version: 1.0
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Precedence: bulk
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Sender: pgsql-hackers-owner@postgresql.org
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Status: OR
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On Fri, 3 Nov 2000, Christof Petig wrote:
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> Karel Zak wrote:
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>
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> > On Thu, 2 Nov 2000, Zeugswetter Andreas SB wrote:
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> >
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> > >
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> > > > Well I can re-write and resubmit this patch. Add it as a
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> > > > compile time option
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> > > > is not bad idea. Second possibility is distribute it as patch
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> > > > in the contrib
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> > > > tree. And if it until not good tested not dirty with this main tree...
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> > > >
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> > > > Ok, I next week prepare it...
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> > >
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> > > One thing that worries me though is, that it extends the sql language,
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> > > and there has been no discussion about the chosen syntax.
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> > >
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> > > Imho the standard embedded SQL syntax (prepare ...) could be a
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> > > starting point.
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> >
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> > Yes, you are right... my PREPARE/EXECUTE is not too much ready to SQL92,
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> > I some old letter I speculate about "SAVE/EXECUTE PLAN" instead
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> > PREPARE/EXECUTE. But don't forget, it will *experimental* patch... we can
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> > change it in future ..etc.
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> >
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> > Karel
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>
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> [Sorry, I didn't look into your patch, yet.]
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Please, read my old query cache and PREPARE/EXECUTE description...
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> What about parameters? Normally you can prepare a statement and execute it
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We have in PG parameters, see SPI, but now it's used inside backend only
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and not exist statement that allows to use this feature in be<->fe.
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> using different parameters. AFAIK postgres' frontend-backend protocol is not
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> designed to take parameters for statements (e.g. like result presents
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> results). A very long road to go.
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> By the way, I'm somewhat interested in getting this feature in. Perhaps it
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> should be part of a protocol redesign (e.g. binary parameters/results).
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> Handling endianness is one aspect, floats are harder (but float->ascii->float
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> sometimes fails as well).
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PREPARE <name> AS <query>
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[ USING type, ... typeN ]
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[ NOSHARE | SHARE | GLOBAL ]
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EXECUTE <name>
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[ INTO [ TEMPORARY | TEMP ] [ TABLE ] new_table ]
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[ USING val, ... valN ]
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[ NOSHARE | SHARE | GLOBAL ]
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DEALLOCATE PREPARE
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[ <name> [ NOSHARE | SHARE | GLOBAL ]]
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[ ALL | ALL INTERNAL ]
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An example:
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PREPARE chris_query AS SELECT * FROM pg_class WHERE relname = $1 USING text;
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EXECUTE chris_query USING 'pg_shadow';
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Or mean you something other?
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Karel
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From pgsql-hackers-owner+M444@postgresql.org Thu Nov 9 03:32:10 2000
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Received: from mail.postgresql.org (webmail.postgresql.org [216.126.85.28])
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(envelope-from pgsql-hackers-owner+M444@postgresql.org)
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Received: from ara.zf.jcu.cz (ara.zf.jcu.cz [160.217.161.4])
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Thu, 9 Nov 2000 09:23:41 +0100
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Date: Thu, 9 Nov 2000 09:23:41 +0100 (CET)
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From: Karel Zak <zakkr@zf.jcu.cz>
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To: Christof Petig <christof.petig@wtal.de>
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cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
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Michael Meskes <meskes@postgresql.org>,
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Zeugswetter Andreas SB <ZeugswetterA@wien.spardat.at>,
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The Hermit Hacker <scrappy@hub.org>
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Subject: Re: AW: [HACKERS] Re: [GENERAL] Query caching
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In-Reply-To: <3A096BCE.F9887955@wtal.de>
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Message-ID: <Pine.LNX.3.96.1001109090739.8052B-100000@ara.zf.jcu.cz>
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MIME-Version: 1.0
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Content-Type: TEXT/PLAIN; charset=US-ASCII
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Precedence: bulk
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Sender: pgsql-hackers-owner@postgresql.org
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Status: OR
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On Wed, 8 Nov 2000, Christof Petig wrote:
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> Karel Zak wrote:
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>
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> > > What about parameters? Normally you can prepare a statement and execute it
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> >
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> > We have in PG parameters, see SPI, but now it's used inside backend only
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> > and not exist statement that allows to use this feature in be<->fe.
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>
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> Sad. Since ecpg would certainly benefit from this.
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>
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> > > using different parameters. AFAIK postgres' frontend-backend protocol is not
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> > > designed to take parameters for statements (e.g. like result presents
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> > > results). A very long road to go.
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> > > By the way, I'm somewhat interested in getting this feature in. Perhaps it
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> > > should be part of a protocol redesign (e.g. binary parameters/results).
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> > > Handling endianness is one aspect, floats are harder (but float->ascii->float
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> > > sometimes fails as well).
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> >
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> > PREPARE <name> AS <query>
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> > [ USING type, ... typeN ]
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> > [ NOSHARE | SHARE | GLOBAL ]
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> >
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> > EXECUTE <name>
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> > [ INTO [ TEMPORARY | TEMP ] [ TABLE ] new_table ]
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> > [ USING val, ... valN ]
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> > [ NOSHARE | SHARE | GLOBAL ]
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> >
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> > DEALLOCATE PREPARE
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> > [ <name> [ NOSHARE | SHARE | GLOBAL ]]
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> > [ ALL | ALL INTERNAL ]
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> >
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> > An example:
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> >
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> > PREPARE chris_query AS SELECT * FROM pg_class WHERE relname = $1 USING text;
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>
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> I would prefer '?' as a parameter name, since this is in the embedded sql standard
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> (do you have a copy of the 94 draft? I can mail mine to you?)
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This not depend on query cache. The '$n' is PostgreSQL query parametr
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keyword and is defined in standard parser. The PREPARE statement not parsing
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query it's job for standard parser.
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> Also the standard says a whole lot about guessing the parameter's type.
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>
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> Also I vote for ?::type or type(?) or sql's cast(...) (don't know it's syntax)
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> instead of abusing the using keyword.
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The postgresql executor expect types of parametrs in separate input (array).
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I not sure how much expensive/executable is survey it from query.
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> > EXECUTE chris_query USING 'pg_shadow';
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>
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> Great idea of yours to implement this! Since I was thinking about implementing a
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> more decent schema for ecpg but had no mind to touch the backend and be-fe
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> protocol (yet).
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> It would be desirable to do an 'execute immediate using', since using input
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> parameters would take a lot of code away from ecpg.
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By the way, PREPARE/EXECUTE is face only. More interesting in this period is
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query-cache-kernel. SQL92 is really a little unlike my PREPARE/EXECUTE.
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Karel
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From pgsql-hackers-owner+M9563@postgresql.org Thu May 31 16:31:59 2001
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Return-path: <pgsql-hackers-owner+M9563@postgresql.org>
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Thu, 31 May 2001 22:23:26 +0200
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Date: Thu, 31 May 2001 22:23:26 +0200
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From: Karel Zak <zakkr@zf.jcu.cz>
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To: Roberto Abalde <roberto.abalde@galego21.org>
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cc: pgsql-hackers@postgresql.org
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Subject: Re: [HACKERS] Cache for query plans
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Message-ID: <20010531222326.B16862@ara.zf.jcu.cz>
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References: <000701c0e932$d17646c0$c6023dc8@ultra>
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MIME-Version: 1.0
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In-Reply-To: <000701c0e932$d17646c0$c6023dc8@ultra>; from roberto.abalde@galego21.org on Wed, May 30, 2001 at 03:00:53PM -0300
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Precedence: bulk
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Sender: pgsql-hackers-owner@postgresql.org
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Status: ORr
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On Wed, May 30, 2001 at 03:00:53PM -0300, Roberto Abalde wrote:
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> Hi,
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>
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> I need to implement a cache for query plans as part of my BSc thesis. Does
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> anybody know what happened to Karel Zak's patch?
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>
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Hi,
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my patch is on my ftp and nobody works on it, but I mean it's good
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begin for some next work. I not sure with implement this experimental
|
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patch (but usable) to official sources. For example Jan has more complex
|
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idea about query plan cache ... but first time we must solve some
|
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sub-problems like memory management in shared memory that is transparently
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for starndard routines like copy query plan ... and Tom isn't sure with
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query cache in shared memory...etc. Too much queries, but less answers :-)
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Karel
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>
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> PS: Sorry for my english :(
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Do you anytime read any my mail :-)
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Karel
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--
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Karel Zak <zakkr@zf.jcu.cz>
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http://home.zf.jcu.cz/~zakkr/
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C, PostgreSQL, PHP, WWW, http://docs.linux.cz, http://mape.jcu.cz
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From pgsql-hackers-owner+M21218@postgresql.org Fri Apr 12 04:52:19 2002
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Return-path: <pgsql-hackers-owner+M21218@postgresql.org>
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Fri, 12 Apr 2002 09:51:16 +0200
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Date: Fri, 12 Apr 2002 09:51:16 +0200
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From: Karel Zak <zakkr@zf.jcu.cz>
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To: pgsql-hackers@postgresql.org
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cc: Hiroshi Inoue <Inoue@tpf.co.jp>
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Subject: Re: [HACKERS] 7.3 schedule
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Message-ID: <20020412095116.B6370@zf.jcu.cz>
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References: <GNELIHDDFBOCMGBFGEFOGEBHCCAA.chriskl@familyhealth.com.au> <3CB52C54.4020507@freaky-namuh.com> <20020411115434.201ff92f.nconway@klamath.dyndns.org> <3CB61DAB.5010601@freaky-namuh.com> <24184.1018581907@sss.pgh.pa.us> <3CB65B49.93F2F790@tpf.co.jp> <20020412004134.5d35a2dd.nconway@klamath.dyndns.org>
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In-Reply-To: <20020412004134.5d35a2dd.nconway@klamath.dyndns.org>; from nconway@klamath.dyndns.org on Fri, Apr 12, 2002 at 12:41:34AM -0400
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Precedence: bulk
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Sender: pgsql-hackers-owner@postgresql.org
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Status: OR
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On Fri, Apr 12, 2002 at 12:41:34AM -0400, Neil Conway wrote:
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> On Fri, 12 Apr 2002 12:58:01 +0900
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> "Hiroshi Inoue" <Inoue@tpf.co.jp> wrote:
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> >
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> > Just a confirmation.
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> > Someone is working on PREPARE/EXECUTE ?
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> > What about Karel's work ?
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Right question :-)
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> I am. My work is based on Karel's stuff -- at the moment I'm still
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> basically working on getting Karel's patch to play nicely with
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> current sources; once that's done I'll be addressing whatever
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> issues are stopping the code from getting into CVS.
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My patch (qcache) for PostgreSQL 7.0 is available at
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ftp://ftp2.zf.jcu.cz/users/zakkr/pg/.
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I very look forward to Neil's work on this.
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Notes:
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* It's experimental patch, but usable. All features below mentioned
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works.
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* PREPARE/EXECUTE is not only SQL statements, I think good idea is
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create something common and robus for query-plan caching,
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beacuse there is for example SPI too. The RI triggers are based
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on SPI_saveplan().
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* My patch knows EXECUTE INTO feature:
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PREPARE foo AS SELECT * FROM pg_class WHERE relname ~~ $1 USING text;
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EXECUTE foo USING 'pg%'; <-- standard select
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EXECUTE foo INTO TEMP newtab USING 'pg%'; <-- select into
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* The patch allows store query-planns to shared memory and is
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possible EXECUTE it at more backends (over same DB) and planns
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are persistent across connetions. For this feature I create special
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memory context subsystem (like current aset.c, but it works with
|
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IPC shared memory).
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This is maybe too complex solution and (maybe) sufficient is cache
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query in one backend only. I know unbelief about this shared
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memory solution (Tom?).
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Karel
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My experimental patch README (excuse my English):
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Implementation
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~~~~~~~~~~~~~~
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The qCache allows save queryTree and queryPlan. There is available are
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two space for data caching.
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LOCAL - data are cached in backend non-shared memory and data aren't
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available in other backends.
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SHARE - data are cached in backend shared memory and data are
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visible in all backends.
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Because size of share memory pool is limited and it is set during
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postmaster start up, the qCache must remove all old planns if pool is
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full. You can mark each entry as "REMOVEABLE" or "NOTREMOVEABLE".
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A removeable entry is removed if pool is full.
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A not-removeable entry must be removed via qCache_Remove() or
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the other routines. The qCache not remove this entry itself.
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All records in qCache are cached (in the hash table) under some key.
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The qCache knows two alternate of key --- "KEY_STRING" and "KEY_BINARY".
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The qCache API not allows access to shared memory, all cached planns that
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API returns are copy to CurrentMemoryContext. All (qCache_ ) routines lock
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shmem itself (exception is qCache_RemoveOldest_ShareRemoveAble()).
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- for locking is used spin lock.
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Memory management
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~~~~~~~~~~~~~~~~~
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The qCache use for qCache's shared pool its memory context independent on
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standard aset/mcxt, but use compatible API --- it allows to use standard
|
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palloc() (it is very needful for basic plan-tree operations, an example
|
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for copyObject()). The qCache memory management is very simular to current
|
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aset.c code. It is chunk-ed blocks too, but the block is smaller - 1024b.
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The number of blocks is available set in postmaster 'argv' via option
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'-Z'.
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For plan storing is used separate MemoryContext for each plan, it
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is good idea (Hiroshi's ?), bucause create new context is simple and
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inexpensive and allows easy destroy (free) cached plan. This method is
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used in my SPI overhaul instead TopMemoryContext feeding.
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Postmaster
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~~~~~~~~~~
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The query cache memory is init during potmaster startup. The size of
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query cache pool is set via '-Z <number-of-blocks>' switch --- default
|
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is 100 blocks where 1 block = 1024b, it is sufficient for 20-30 cached
|
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planns. One query needs somewhere 3-10 blocks, for example query like
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PREPARE sel AS SELECT * FROM pg_class;
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needs 10Kb, because table pg_class has very much columns.
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Note: for development I add SQL function: "SELECT qcache_state();",
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this routine show usage of qCache.
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SPI
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~~~
|
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I a little overwrite SPI save plan method and remove TopMemoryContext
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"feeding".
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Standard SPI:
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SPI_saveplan() - save each plan to separate standard memory context.
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SPI_freeplan() - free plan.
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By key SPI:
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It is SPI interface for query cache and allows save planns to SHARED
|
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or LOCAL cache 'by' arbitrary key (string or binary). Routines:
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SPI_saveplan_bykey() - save plan to query cache
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|
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SPI_freeplan_bykey() - remove plan from query cache
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SPI_fetchplan_bykey() - fetch plan saved in query cache
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|
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SPI_execp_bykey() - execute (via SPI) plan saved in query
|
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cache
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|
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- now, users can write functions that save planns to shared memory
|
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and planns are visible in all backend and are persistent arcoss
|
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connection.
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Example:
|
|
~~~~~~~
|
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/* ----------
|
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* Save/exec query from shared cache via string key
|
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* ----------
|
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*/
|
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int keySize = 0;
|
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flag = SPI_BYKEY_SHARE | SPI_BYKEY_STRING;
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char *key = "my unique key";
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res = SPI_execp_bykey(values, nulls, tcount, key, flag, keySize);
|
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|
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if (res == SPI_ERROR_PLANNOTFOUND)
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{
|
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/* --- not plan in cache - must create it --- */
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void *plan;
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plan = SPI_prepare(querystr, valnum, valtypes);
|
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SPI_saveplan_bykey(plan, key, keySize, flag);
|
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|
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res = SPI_execute(plan, values, Nulls, tcount);
|
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}
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|
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elog(NOTICE, "Processed: %d", SPI_processed);
|
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PREPARE/EXECUTE
|
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~~~~~~~~~~~~~~~
|
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* Syntax:
|
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PREPARE <name> AS <query>
|
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[ USING type, ... typeN ]
|
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[ NOSHARE | SHARE | GLOBAL ]
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EXECUTE <name>
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[ INTO [ TEMPORARY | TEMP ] [ TABLE ] new_table ]
|
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[ USING val, ... valN ]
|
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[ NOSHARE | SHARE | GLOBAL ]
|
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DEALLOCATE PREPARE
|
|
[ <name> [ NOSHARE | SHARE | GLOBAL ]]
|
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[ ALL | ALL INTERNAL ]
|
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|
|
I know that it is a little out of SQL92... (use CREATE/DROP PLAN instead
|
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this?) --- what mean SQL standard guru?
|
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|
|
* Where:
|
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|
|
NOSHARE --- cached in local backend query cache - not accessable
|
|
from the others backends and not is persisten a across
|
|
conection.
|
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|
|
SHARE --- cached in shared query cache and accessable from
|
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all backends which work over same database.
|
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|
|
GLOBAL --- cached in shared query cache and accessable from
|
|
all backends and all databases.
|
|
|
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- default is 'SHARE'
|
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|
|
Deallocate:
|
|
|
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ALL --- deallocate all users's plans
|
|
|
|
ALL INTERNAL --- deallocate all internal plans, like planns
|
|
cached via SPI. It is needful if user
|
|
alter/drop table ...etc.
|
|
|
|
* Parameters:
|
|
|
|
"USING" part in the prepare statement is for datetype setting for
|
|
paremeters in the query. For example:
|
|
|
|
PREPARE sel AS SELECT * FROM pg_class WHERE relname ~~ $1 USING text;
|
|
|
|
EXECUTE sel USING 'pg%';
|
|
|
|
|
|
* Limitation:
|
|
|
|
- prepare/execute allow use full statement of SELECT/INSERT/DELETE/
|
|
UPDATE.
|
|
- possible is use union, subselects, limit, ofset, select-into
|
|
|
|
|
|
Performance:
|
|
~~~~~~~~~~~
|
|
* the SPI
|
|
|
|
- I for my tests a little change RI triggers to use SPI by_key API
|
|
and save planns to shared qCache instead to internal RI hash table.
|
|
|
|
The RI use very simple (for parsing) queries and qCache interest is
|
|
not visible. It's better if backend very often startup and RI check
|
|
always same tables. In this situation speed go up --- 10-12%.
|
|
(This snapshot not include this RI change.)
|
|
|
|
But all depend on how much complicate for parser is query in
|
|
trigger.
|
|
|
|
* PREPARE/EXECUTE
|
|
|
|
- For tests I use query that not use some table (the executor is
|
|
in boredom state), but is difficult for the parser. An example:
|
|
|
|
SELECT 'a text ' || (10*10+(100^2))::text || ' next text ' || cast
|
|
(date_part('year', timestamp 'now') AS text );
|
|
|
|
- (10000 * this query):
|
|
|
|
standard select: 54 sec
|
|
via prepare/execute: 4 sec (93% better)
|
|
|
|
IMHO it is nod bad.
|
|
|
|
- For standard query like:
|
|
|
|
SELECT u.usename, r.relname FROM pg_class r, pg_user u WHERE
|
|
r.relowner = u.usesysid;
|
|
|
|
it is with PREPARE/EXECUTE 10-20% faster.
|
|
|
|
--
|
|
Karel Zak <zakkr@zf.jcu.cz>
|
|
http://home.zf.jcu.cz/~zakkr/
|
|
|
|
C, PostgreSQL, PHP, WWW, http://docs.linux.cz, http://mape.jcu.cz
|
|
|
|
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TIP 4: Don't 'kill -9' the postmaster
|
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From pgsql-hackers-owner+M21228@postgresql.org Fri Apr 12 10:15:34 2002
|
|
Return-path: <pgsql-hackers-owner+M21228@postgresql.org>
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Received: from postgresql.org (postgresql.org [64.49.215.8])
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|
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|
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Fri, 12 Apr 2002 10:14:26 -0400 (EDT)
|
|
To: Karel Zak <zakkr@zf.jcu.cz>
|
|
cc: pgsql-hackers@postgresql.org, Neil Conway <nconway@klamath.dyndns.org>
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
In-Reply-To: <20020412095116.B6370@zf.jcu.cz>
|
|
References: <GNELIHDDFBOCMGBFGEFOGEBHCCAA.chriskl@familyhealth.com.au> <3CB52C54.4020507@freaky-namuh.com> <20020411115434.201ff92f.nconway@klamath.dyndns.org> <3CB61DAB.5010601@freaky-namuh.com> <24184.1018581907@sss.pgh.pa.us> <3CB65B49.93F2F790@tpf.co.jp> <20020412004134.5d35a2dd.nconway@klamath.dyndns.org> <20020412095116.B6370@zf.jcu.cz>
|
|
Comments: In-reply-to Karel Zak <zakkr@zf.jcu.cz>
|
|
message dated "Fri, 12 Apr 2002 09:51:16 +0200"
|
|
Date: Fri, 12 Apr 2002 10:14:26 -0400
|
|
Message-ID: <27235.1018620866@sss.pgh.pa.us>
|
|
From: Tom Lane <tgl@sss.pgh.pa.us>
|
|
Precedence: bulk
|
|
Sender: pgsql-hackers-owner@postgresql.org
|
|
Status: ORr
|
|
|
|
Karel Zak <zakkr@zf.jcu.cz> writes:
|
|
> * The patch allows store query-planns to shared memory and is
|
|
> possible EXECUTE it at more backends (over same DB) and planns
|
|
> are persistent across connetions. For this feature I create special
|
|
> memory context subsystem (like current aset.c, but it works with
|
|
> IPC shared memory).
|
|
> This is maybe too complex solution and (maybe) sufficient is cache
|
|
> query in one backend only. I know unbelief about this shared
|
|
> memory solution (Tom?).
|
|
|
|
Yes, that is the part that was my sticking point last time around.
|
|
(1) Because shared memory cannot be extended on-the-fly, I think it is
|
|
a very bad idea to put data structures in there without some well
|
|
thought out way of predicting/limiting their size. (2) How the heck do
|
|
you get rid of obsoleted cached plans, if the things stick around in
|
|
shared memory even after you start a new backend? (3) A shared cache
|
|
requires locking; contention among multiple backends to access that
|
|
shared resource could negate whatever performance benefit you might hope
|
|
to realize from it.
|
|
|
|
A per-backend cache kept in local memory avoids all of these problems,
|
|
and I have seen no numbers to make me think that a shared plan cache
|
|
would achieve significantly more performance benefit than a local one.
|
|
|
|
regards, tom lane
|
|
|
|
---------------------------(end of broadcast)---------------------------
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TIP 5: Have you checked our extensive FAQ?
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http://www.postgresql.org/users-lounge/docs/faq.html
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From pgsql-hackers-owner+M21233@postgresql.org Fri Apr 12 12:26:32 2002
|
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Return-path: <pgsql-hackers-owner+M21233@postgresql.org>
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Received: from postgresql.org (postgresql.org [64.49.215.8])
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by candle.pha.pa.us (8.11.6/8.10.1) id g3CGL4310492;
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Fri, 12 Apr 2002 12:21:04 -0400 (EDT)
|
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From: Bruce Momjian <pgman@candle.pha.pa.us>
|
|
Message-ID: <200204121621.g3CGL4310492@candle.pha.pa.us>
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
In-Reply-To: <27235.1018620866@sss.pgh.pa.us>
|
|
To: Tom Lane <tgl@sss.pgh.pa.us>
|
|
Date: Fri, 12 Apr 2002 12:21:04 -0400 (EDT)
|
|
cc: Karel Zak <zakkr@zf.jcu.cz>, pgsql-hackers@postgresql.org,
|
|
Neil Conway <nconway@klamath.dyndns.org>
|
|
X-Mailer: ELM [version 2.4ME+ PL97 (25)]
|
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MIME-Version: 1.0
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Precedence: bulk
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Sender: pgsql-hackers-owner@postgresql.org
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Status: OR
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Tom Lane wrote:
|
|
> Karel Zak <zakkr@zf.jcu.cz> writes:
|
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> > * The patch allows store query-planns to shared memory and is
|
|
> > possible EXECUTE it at more backends (over same DB) and planns
|
|
> > are persistent across connetions. For this feature I create special
|
|
> > memory context subsystem (like current aset.c, but it works with
|
|
> > IPC shared memory).
|
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> > This is maybe too complex solution and (maybe) sufficient is cache
|
|
> > query in one backend only. I know unbelief about this shared
|
|
> > memory solution (Tom?).
|
|
>
|
|
> Yes, that is the part that was my sticking point last time around.
|
|
> (1) Because shared memory cannot be extended on-the-fly, I think it is
|
|
> a very bad idea to put data structures in there without some well
|
|
> thought out way of predicting/limiting their size. (2) How the heck do
|
|
> you get rid of obsoleted cached plans, if the things stick around in
|
|
> shared memory even after you start a new backend? (3) A shared cache
|
|
> requires locking; contention among multiple backends to access that
|
|
> shared resource could negate whatever performance benefit you might hope
|
|
> to realize from it.
|
|
>
|
|
> A per-backend cache kept in local memory avoids all of these problems,
|
|
> and I have seen no numbers to make me think that a shared plan cache
|
|
> would achieve significantly more performance benefit than a local one.
|
|
|
|
Certainly a shared cache would be good for apps that connect to issue a
|
|
single query frequently. In such cases, there would be no local cache
|
|
to use.
|
|
|
|
--
|
|
Bruce Momjian | http://candle.pha.pa.us
|
|
pgman@candle.pha.pa.us | (610) 853-3000
|
|
+ If your life is a hard drive, | 830 Blythe Avenue
|
|
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
|
|
|
|
---------------------------(end of broadcast)---------------------------
|
|
TIP 4: Don't 'kill -9' the postmaster
|
|
|
|
From pgsql-hackers-owner+M21234@postgresql.org Fri Apr 12 12:44:12 2002
|
|
Return-path: <pgsql-hackers-owner+M21234@postgresql.org>
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|
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Received: from barry.xythos.com (h-64-105-36-191.SNVACAID.covad.net [64.105.36.191])
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Fri, 12 Apr 2002 09:42:36 -0700
|
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Message-ID: <3CB70E7C.3090801@xythos.com>
|
|
Date: Fri, 12 Apr 2002 09:42:36 -0700
|
|
From: Barry Lind <barry@xythos.com>
|
|
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.9) Gecko/20020310
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MIME-Version: 1.0
|
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To: Tom Lane <tgl@sss.pgh.pa.us>
|
|
cc: Karel Zak <zakkr@zf.jcu.cz>, pgsql-hackers@postgresql.org,
|
|
Neil Conway <nconway@klamath.dyndns.org>
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
References: <GNELIHDDFBOCMGBFGEFOGEBHCCAA.chriskl@familyhealth.com.au> <3CB52C54.4020507@freaky-namuh.com> <20020411115434.201ff92f.nconway@klamath.dyndns.org> <3CB61DAB.5010601@freaky-namuh.com> <24184.1018581907@sss.pgh.pa.us> <3CB65B49.93F2F790@tpf.co.jp> <20020412004134.5d35a2dd.nconway@klamath.dyndns.org> <20020412095116.B6370@zf.jcu.cz> <27235.1018620866@sss.pgh.pa.us>
|
|
Content-Type: text/plain; charset=us-ascii; format=flowed
|
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Content-Transfer-Encoding: 7bit
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|
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Sender: pgsql-hackers-owner@postgresql.org
|
|
Status: ORr
|
|
|
|
|
|
|
|
Tom Lane wrote:
|
|
> Yes, that is the part that was my sticking point last time around.
|
|
> (1) Because shared memory cannot be extended on-the-fly, I think it is
|
|
> a very bad idea to put data structures in there without some well
|
|
> thought out way of predicting/limiting their size. (2) How the heck do
|
|
> you get rid of obsoleted cached plans, if the things stick around in
|
|
> shared memory even after you start a new backend? (3) A shared cache
|
|
> requires locking; contention among multiple backends to access that
|
|
> shared resource could negate whatever performance benefit you might hope
|
|
> to realize from it.
|
|
>
|
|
> A per-backend cache kept in local memory avoids all of these problems,
|
|
> and I have seen no numbers to make me think that a shared plan cache
|
|
> would achieve significantly more performance benefit than a local one.
|
|
>
|
|
|
|
Oracle's implementation is a shared cache for all plans. This was
|
|
introduced in Oracle 6 or 7 (I don't remember which anymore). The net
|
|
effect was that in general there was a significant performance
|
|
improvement with the shared cache. However poorly written apps can now
|
|
bring the Oracle database to its knees because of the locking issues
|
|
associated with the shared cache. For example if the most frequently
|
|
run sql statements are coded poorly (i.e. they don't use bind variables,
|
|
eg. 'select bar from foo where foobar = $1' vs. 'select bar from foo
|
|
where foobar = || somevalue' (where somevalue is likely to be
|
|
different on every call)) the shared cache doesn't help and its overhead
|
|
becomes significant.
|
|
|
|
thanks,
|
|
--Barry
|
|
|
|
|
|
|
|
---------------------------(end of broadcast)---------------------------
|
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TIP 3: if posting/reading through Usenet, please send an appropriate
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subscribe-nomail command to majordomo@postgresql.org so that your
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From pgsql-hackers-owner+M21237@postgresql.org Fri Apr 12 12:50:28 2002
|
|
Return-path: <pgsql-hackers-owner+M21237@postgresql.org>
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by candle.pha.pa.us (8.11.6/8.10.1) id g3CGnbw12950;
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Fri, 12 Apr 2002 12:49:37 -0400 (EDT)
|
|
From: Bruce Momjian <pgman@candle.pha.pa.us>
|
|
Message-ID: <200204121649.g3CGnbw12950@candle.pha.pa.us>
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
In-Reply-To: <3CB70E7C.3090801@xythos.com>
|
|
To: Barry Lind <barry@xythos.com>
|
|
Date: Fri, 12 Apr 2002 12:49:37 -0400 (EDT)
|
|
cc: Tom Lane <tgl@sss.pgh.pa.us>, Karel Zak <zakkr@zf.jcu.cz>,
|
|
pgsql-hackers@postgresql.org, Neil Conway <nconway@klamath.dyndns.org>
|
|
X-Mailer: ELM [version 2.4ME+ PL97 (25)]
|
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|
Precedence: bulk
|
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Sender: pgsql-hackers-owner@postgresql.org
|
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Status: OR
|
|
|
|
Barry Lind wrote:
|
|
> Oracle's implementation is a shared cache for all plans. This was
|
|
> introduced in Oracle 6 or 7 (I don't remember which anymore). The net
|
|
> effect was that in general there was a significant performance
|
|
> improvement with the shared cache. However poorly written apps can now
|
|
> bring the Oracle database to its knees because of the locking issues
|
|
> associated with the shared cache. For example if the most frequently
|
|
> run sql statements are coded poorly (i.e. they don't use bind variables,
|
|
> eg. 'select bar from foo where foobar = $1' vs. 'select bar from foo
|
|
> where foobar = || somevalue' (where somevalue is likely to be
|
|
> different on every call)) the shared cache doesn't help and its overhead
|
|
> becomes significant.
|
|
|
|
This is very interesting. We have always been concerned that shared
|
|
cache invalidation could cause more of a performance problem that the
|
|
shared cache gives benefit, and it sounds like you are saying exactly
|
|
that.
|
|
|
|
--
|
|
Bruce Momjian | http://candle.pha.pa.us
|
|
pgman@candle.pha.pa.us | (610) 853-3000
|
|
+ If your life is a hard drive, | 830 Blythe Avenue
|
|
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
|
|
|
|
---------------------------(end of broadcast)---------------------------
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|
TIP 2: you can get off all lists at once with the unregister command
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(send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
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From pgsql-hackers-owner+M21238@postgresql.org Fri Apr 12 12:51:55 2002
|
|
Return-path: <pgsql-hackers-owner+M21238@postgresql.org>
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Fri, 12 Apr 2002 12:51:27 -0400 (EDT)
|
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To: Bruce Momjian <pgman@candle.pha.pa.us>
|
|
cc: Karel Zak <zakkr@zf.jcu.cz>, pgsql-hackers@postgresql.org,
|
|
Neil Conway <nconway@klamath.dyndns.org>
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
In-Reply-To: <200204121621.g3CGL4310492@candle.pha.pa.us>
|
|
References: <200204121621.g3CGL4310492@candle.pha.pa.us>
|
|
Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
|
|
message dated "Fri, 12 Apr 2002 12:21:04 -0400"
|
|
Date: Fri, 12 Apr 2002 12:51:26 -0400
|
|
Message-ID: <27964.1018630286@sss.pgh.pa.us>
|
|
From: Tom Lane <tgl@sss.pgh.pa.us>
|
|
Precedence: bulk
|
|
Sender: pgsql-hackers-owner@postgresql.org
|
|
Status: OR
|
|
|
|
Bruce Momjian <pgman@candle.pha.pa.us> writes:
|
|
> Certainly a shared cache would be good for apps that connect to issue a
|
|
> single query frequently. In such cases, there would be no local cache
|
|
> to use.
|
|
|
|
We have enough other problems with the single-query-per-connection
|
|
scenario that I see no reason to believe that a shared plan cache will
|
|
help materially. The correct answer for those folks will *always* be
|
|
to find a way to reuse the connection.
|
|
|
|
regards, tom lane
|
|
|
|
---------------------------(end of broadcast)---------------------------
|
|
TIP 4: Don't 'kill -9' the postmaster
|
|
|
|
From pgsql-hackers-owner+M21241@postgresql.org Fri Apr 12 16:25:46 2002
|
|
Return-path: <pgsql-hackers-owner+M21241@postgresql.org>
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id C05557013; Fri, 12 Apr 2002 16:24:53 -0400 (EDT)
|
|
Date: Fri, 12 Apr 2002 16:24:48 -0400
|
|
From: Neil Conway <nconway@klamath.dyndns.org>
|
|
To: "Bruce Momjian" <pgman@candle.pha.pa.us>
|
|
cc: tgl@sss.pgh.pa.us, zakkr@zf.jcu.cz, pgsql-hackers@postgresql.org
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
Message-ID: <20020412162448.4d46d747.nconway@klamath.dyndns.org>
|
|
In-Reply-To: <200204121621.g3CGL4310492@candle.pha.pa.us>
|
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References: <27235.1018620866@sss.pgh.pa.us>
|
|
<200204121621.g3CGL4310492@candle.pha.pa.us>
|
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X-Mailer: Sylpheed version 0.7.4 (GTK+ 1.2.10; i386-debian-linux-gnu)
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Status: ORr
|
|
|
|
On Fri, 12 Apr 2002 12:21:04 -0400 (EDT)
|
|
"Bruce Momjian" <pgman@candle.pha.pa.us> wrote:
|
|
> Tom Lane wrote:
|
|
> > A per-backend cache kept in local memory avoids all of these problems,
|
|
> > and I have seen no numbers to make me think that a shared plan cache
|
|
> > would achieve significantly more performance benefit than a local one.
|
|
>
|
|
> Certainly a shared cache would be good for apps that connect to issue a
|
|
> single query frequently. In such cases, there would be no local cache
|
|
> to use.
|
|
|
|
One problem with this kind of scenario is: what to do if the plan no
|
|
longer exists for some reason? (e.g. the code that was supposed to be
|
|
PREPARE-ing your statements failed to execute properly, or the cached
|
|
plan has been evicted from shared memory, or the database was restarted,
|
|
etc.) -- EXECUTE in and of itself won't have enough information to do
|
|
anything useful. We could perhaps provide a means for an application
|
|
to test for the existence of a cached plan (in which case the
|
|
application developer will need to add logic to their application
|
|
to re-prepare the query if necessary, which could get complicated).
|
|
|
|
Cheers,
|
|
|
|
Neil
|
|
|
|
--
|
|
Neil Conway <neilconway@rogers.com>
|
|
PGP Key ID: DB3C29FC
|
|
|
|
---------------------------(end of broadcast)---------------------------
|
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TIP 5: Have you checked our extensive FAQ?
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|
http://www.postgresql.org/users-lounge/docs/faq.html
|
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|
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From pgsql-hackers-owner+M21242@postgresql.org Fri Apr 12 17:27:24 2002
|
|
Return-path: <pgsql-hackers-owner+M21242@postgresql.org>
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Fri, 12 Apr 2002 17:25:31 -0400 (EDT)
|
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From: Bruce Momjian <pgman@candle.pha.pa.us>
|
|
Message-ID: <200204122125.g3CLPVa14231@candle.pha.pa.us>
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
In-Reply-To: <20020412162448.4d46d747.nconway@klamath.dyndns.org>
|
|
To: Neil Conway <nconway@klamath.dyndns.org>
|
|
Date: Fri, 12 Apr 2002 17:25:31 -0400 (EDT)
|
|
cc: tgl@sss.pgh.pa.us, zakkr@zf.jcu.cz, pgsql-hackers@postgresql.org
|
|
X-Mailer: ELM [version 2.4ME+ PL97 (25)]
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|
Precedence: bulk
|
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Sender: pgsql-hackers-owner@postgresql.org
|
|
Status: OR
|
|
|
|
Neil Conway wrote:
|
|
> On Fri, 12 Apr 2002 12:21:04 -0400 (EDT)
|
|
> "Bruce Momjian" <pgman@candle.pha.pa.us> wrote:
|
|
> > Tom Lane wrote:
|
|
> > > A per-backend cache kept in local memory avoids all of these problems,
|
|
> > > and I have seen no numbers to make me think that a shared plan cache
|
|
> > > would achieve significantly more performance benefit than a local one.
|
|
> >
|
|
> > Certainly a shared cache would be good for apps that connect to issue a
|
|
> > single query frequently. In such cases, there would be no local cache
|
|
> > to use.
|
|
>
|
|
> One problem with this kind of scenario is: what to do if the plan no
|
|
> longer exists for some reason? (e.g. the code that was supposed to be
|
|
> PREPARE-ing your statements failed to execute properly, or the cached
|
|
> plan has been evicted from shared memory, or the database was restarted,
|
|
> etc.) -- EXECUTE in and of itself won't have enough information to do
|
|
> anything useful. We could perhaps provide a means for an application
|
|
> to test for the existence of a cached plan (in which case the
|
|
> application developer will need to add logic to their application
|
|
> to re-prepare the query if necessary, which could get complicated).
|
|
|
|
Oh, are you thinking that one backend would do the PREPARE and another
|
|
one the EXECUTE? I can't see that working at all. I thought there
|
|
would some way to quickly test if the submitted query was in the cache,
|
|
but maybe that is too much of a performance penalty to be worth it.
|
|
|
|
--
|
|
Bruce Momjian | http://candle.pha.pa.us
|
|
pgman@candle.pha.pa.us | (610) 853-3000
|
|
+ If your life is a hard drive, | 830 Blythe Avenue
|
|
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
|
|
|
|
---------------------------(end of broadcast)---------------------------
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From tgl@sss.pgh.pa.us Fri Apr 12 17:36:17 2002
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To: Bruce Momjian <pgman@candle.pha.pa.us>
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cc: Neil Conway <nconway@klamath.dyndns.org>, zakkr@zf.jcu.cz,
|
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pgsql-hackers@postgresql.org
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Subject: Re: [HACKERS] 7.3 schedule
|
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In-Reply-To: <200204122125.g3CLPVa14231@candle.pha.pa.us>
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References: <200204122125.g3CLPVa14231@candle.pha.pa.us>
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Comments: In-reply-to Bruce Momjian <pgman@candle.pha.pa.us>
|
|
message dated "Fri, 12 Apr 2002 17:25:31 -0400"
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Date: Fri, 12 Apr 2002 17:36:16 -0400
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Message-ID: <10810.1018647376@sss.pgh.pa.us>
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From: Tom Lane <tgl@sss.pgh.pa.us>
|
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Status: ORr
|
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
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> Oh, are you thinking that one backend would do the PREPARE and another
|
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> one the EXECUTE? I can't see that working at all.
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Uh, why exactly were you advocating a shared cache then? Wouldn't that
|
|
be exactly the *point* of a shared cache?
|
|
|
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regards, tom lane
|
|
|
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From pgsql-hackers-owner+M21245@postgresql.org Fri Apr 12 17:39:13 2002
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Fri, 12 Apr 2002 17:38:15 -0400 (EDT)
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From: Bruce Momjian <pgman@candle.pha.pa.us>
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Message-ID: <200204122138.g3CLcFX16347@candle.pha.pa.us>
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Subject: Re: [HACKERS] 7.3 schedule
|
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In-Reply-To: <10810.1018647376@sss.pgh.pa.us>
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To: Tom Lane <tgl@sss.pgh.pa.us>
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Date: Fri, 12 Apr 2002 17:38:15 -0400 (EDT)
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cc: Neil Conway <nconway@klamath.dyndns.org>, zakkr@zf.jcu.cz,
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pgsql-hackers@postgresql.org
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Status: OR
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|
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Tom Lane wrote:
|
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> Bruce Momjian <pgman@candle.pha.pa.us> writes:
|
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> > Oh, are you thinking that one backend would do the PREPARE and another
|
|
> > one the EXECUTE? I can't see that working at all.
|
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>
|
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> Uh, why exactly were you advocating a shared cache then? Wouldn't that
|
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> be exactly the *point* of a shared cache?
|
|
|
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I thought it would somehow compare the SQL query string to the cached
|
|
plans and if it matched, it would use that plan rather than make a new
|
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one. Any DDL statement would flush the cache.
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|
|
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--
|
|
Bruce Momjian | http://candle.pha.pa.us
|
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pgman@candle.pha.pa.us | (610) 853-3000
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+ If your life is a hard drive, | 830 Blythe Avenue
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+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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From pgsql-hackers-owner+M21246@postgresql.org Fri Apr 12 17:56:58 2002
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Subject: Re: [HACKERS] 7.3 schedule
|
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Date: Fri, 12 Apr 2002 14:59:15 -0700
|
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Message-ID: <D90A5A6C612A39408103E6ECDD77B82906F42C@voyager.corporate.connx.com>
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Thread-Topic: [HACKERS] 7.3 schedule
|
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Thread-Index: AcHia2aODSpgXEd4Tluz/N0jN5fJOQAAC//w
|
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From: "Dann Corbit" <DCorbit@connx.com>
|
|
To: "Bruce Momjian" <pgman@candle.pha.pa.us>, "Tom Lane" <tgl@sss.pgh.pa.us>
|
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cc: "Neil Conway" <nconway@klamath.dyndns.org>, <zakkr@zf.jcu.cz>,
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<pgsql-hackers@postgresql.org>
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Status: OR
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-----Original Message-----
|
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From: Bruce Momjian [mailto:pgman@candle.pha.pa.us]
|
|
Sent: Friday, April 12, 2002 2:38 PM
|
|
To: Tom Lane
|
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Cc: Neil Conway; zakkr@zf.jcu.cz; pgsql-hackers@postgresql.org
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
|
|
|
|
Tom Lane wrote:
|
|
> Bruce Momjian <pgman@candle.pha.pa.us> writes:
|
|
> > Oh, are you thinking that one backend would do the PREPARE and
|
|
another
|
|
> > one the EXECUTE? I can't see that working at all.
|
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>
|
|
> Uh, why exactly were you advocating a shared cache then? Wouldn't
|
|
that
|
|
> be exactly the *point* of a shared cache?
|
|
|
|
I thought it would somehow compare the SQL query string to the cached
|
|
plans and if it matched, it would use that plan rather than make a new
|
|
one. Any DDL statement would flush the cache.
|
|
>>-------------------------------------------------------------------
|
|
Many applications will have similar queries coming from lots of
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different end-users. Imagine an order-entry program where people are
|
|
ordering parts. Many of the queries might look like this:
|
|
|
|
SELECT part_number FROM parts WHERE part_id = 12324 AND part_cost
|
|
< 12.95
|
|
|
|
In order to cache this query, we first parse it to replace the data
|
|
fields with paramter markers.
|
|
Then it looks like this:
|
|
SELECT part_number FROM parts WHERE part_id = ? AND part_cost < ?
|
|
{in the case of a 'LIKE' query or some other query where you can use
|
|
key information, you might have a symbolic replacement like this:
|
|
WHERE field LIKE '{D}%' to indicate that the key can be used}
|
|
Then, we make sure that the case is consistent by either capitalizing
|
|
the whole query or changing it all into lower case:
|
|
select part_number from parts where part_id = ? and part_cost < ?
|
|
Then, we run a checksum on the parameterized string.
|
|
The checksum might be used as a hash table key, where we keep some
|
|
additional information like how stale the entry is, and a pointer to
|
|
the actual parameterized SQL (in case the hash key has a collision
|
|
it would be simply wrong to run an incorrect query for obvious enough
|
|
reasons).
|
|
Now, if there are a huge number of users of the same application, it
|
|
makes sense that the probabilities of reusing queries goes up with
|
|
the number of users of the same application. Therefore, I would
|
|
advocate that the cache be kept in shared memory.
|
|
|
|
Consider a single application with 100 different queries. Now, add
|
|
one user, ten users, 100 users, ... 10,000 users and you can see
|
|
that the benefit would be greater and greater as we add users.
|
|
<<-------------------------------------------------------------------
|
|
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|
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From pgsql-hackers-owner+M21270@postgresql.org Sat Apr 13 02:30:47 2002
|
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Message-ID: <002301c1e2b3$804bd000$0200a8c0@SOL>
|
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From: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
|
|
To: "Barry Lind" <barry@xythos.com>, "Tom Lane" <tgl@sss.pgh.pa.us>
|
|
cc: "Karel Zak" <zakkr@zf.jcu.cz>, <pgsql-hackers@postgresql.org>,
|
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"Neil Conway" <nconway@klamath.dyndns.org>
|
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References: <GNELIHDDFBOCMGBFGEFOGEBHCCAA.chriskl@familyhealth.com.au> <3CB52C54.4020507@freaky-namuh.com> <20020411115434.201ff92f.nconway@klamath.dyndns.org> <3CB61DAB.5010601@freaky-namuh.com> <24184.1018581907@sss.pgh.pa.us> <3CB65B49.93F2F790@tpf.co.jp> <20020412004134.5d35a2dd.nconway@klamath.dyndns.org> <20020412095116.B6370@zf.jcu.cz> <27235.1018620866@sss.pgh.pa.us> <3CB70E7C.3090801@xythos.com>
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Subject: Re: [HACKERS] 7.3 schedule
|
|
Date: Sat, 13 Apr 2002 14:21:50 +0800
|
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MIME-Version: 1.0
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Status: OR
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|
|
> > thought out way of predicting/limiting their size. (2) How the heck do
|
|
> > you get rid of obsoleted cached plans, if the things stick around in
|
|
> > shared memory even after you start a new backend? (3) A shared cache
|
|
> > requires locking; contention among multiple backends to access that
|
|
> > shared resource could negate whatever performance benefit you might hope
|
|
> > to realize from it.
|
|
|
|
I don't understand all these locking problems? Surely the only lock a
|
|
transaction would need on a stored query is one that prevents the cache
|
|
invalidation mechanism from deleting it out from under it? Surely this
|
|
means that there would be tonnes of readers on the cache - none of them
|
|
blocking each other, and the odd invalidation event that needs a complete
|
|
lock?
|
|
|
|
Also, as for invalidation, there probably could be just two reasons to
|
|
invalidate a query in the cache. (1) The cache is running out of space and
|
|
you use LRU or something to remove old queries, or (2) someone runs ANALYZE,
|
|
in which case all cached queries should just be flushed? If they specify an
|
|
actual table to analyze, then just drop all queries on the table.
|
|
|
|
Could this cache mechanism be used to make views fast as well? You could
|
|
cache the queries that back views on first use, and then they can follow the
|
|
above rules for flushing...
|
|
|
|
Chris
|
|
|
|
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|
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From pgsql-hackers-owner+M21276@postgresql.org Sat Apr 13 11:48:51 2002
|
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Return-path: <pgsql-hackers-owner+M21276@postgresql.org>
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Sat, 13 Apr 2002 11:46:02 -0400 (EDT)
|
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To: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
|
|
cc: "Barry Lind" <barry@xythos.com>, "Karel Zak" <zakkr@zf.jcu.cz>,
|
|
pgsql-hackers@postgresql.org, "Neil Conway" <nconway@klamath.dyndns.org>
|
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Subject: Re: [HACKERS] 7.3 schedule
|
|
In-Reply-To: <002301c1e2b3$804bd000$0200a8c0@SOL>
|
|
References: <GNELIHDDFBOCMGBFGEFOGEBHCCAA.chriskl@familyhealth.com.au> <3CB52C54.4020507@freaky-namuh.com> <20020411115434.201ff92f.nconway@klamath.dyndns.org> <3CB61DAB.5010601@freaky-namuh.com> <24184.1018581907@sss.pgh.pa.us> <3CB65B49.93F2F790@tpf.co.jp> <20020412004134.5d35a2dd.nconway@klamath.dyndns.org> <20020412095116.B6370@zf.jcu.cz> <27235.1018620866@sss.pgh.pa.us> <3CB70E7C.3090801@xythos.com> <002301c1e2b3$804bd000$0200a8c0@SOL>
|
|
Comments: In-reply-to "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
|
|
message dated "Sat, 13 Apr 2002 14:21:50 +0800"
|
|
Date: Sat, 13 Apr 2002 11:46:01 -0400
|
|
Message-ID: <15740.1018712761@sss.pgh.pa.us>
|
|
From: Tom Lane <tgl@sss.pgh.pa.us>
|
|
Precedence: bulk
|
|
Sender: pgsql-hackers-owner@postgresql.org
|
|
Status: OR
|
|
|
|
"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
|
|
> thought out way of predicting/limiting their size. (2) How the heck do
|
|
> you get rid of obsoleted cached plans, if the things stick around in
|
|
> shared memory even after you start a new backend? (3) A shared cache
|
|
> requires locking; contention among multiple backends to access that
|
|
> shared resource could negate whatever performance benefit you might hope
|
|
> to realize from it.
|
|
|
|
> I don't understand all these locking problems?
|
|
|
|
Searching the cache and inserting/deleting entries in the cache probably
|
|
have to be mutually exclusive; concurrent insertions probably won't work
|
|
either (at least not without a remarkably intelligent data structure).
|
|
Unless the cache hit rate is remarkably high, there are going to be lots
|
|
of insertions --- and, at steady state, an equal rate of deletions ---
|
|
leading to lots of contention.
|
|
|
|
This could possibly be avoided if the cache is not used for all query
|
|
plans but only for explicitly PREPAREd plans, so that only explicit
|
|
EXECUTEs would need to search it. But that approach also makes a
|
|
sizable dent in the usefulness of the cache to begin with.
|
|
|
|
regards, tom lane
|
|
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|
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From pgsql-hackers-owner+M21280@postgresql.org Sat Apr 13 14:36:34 2002
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Return-path: <pgsql-hackers-owner+M21280@postgresql.org>
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id 82B84700C; Sat, 13 Apr 2002 14:35:42 -0400 (EDT)
|
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Date: Sat, 13 Apr 2002 14:35:39 -0400
|
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From: Neil Conway <nconway@klamath.dyndns.org>
|
|
To: "Christopher Kings-Lynne" <chriskl@familyhealth.com.au>
|
|
cc: barry@xythos.com, tgl@sss.pgh.pa.us, zakkr@zf.jcu.cz,
|
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pgsql-hackers@postgresql.org
|
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Subject: Re: [HACKERS] 7.3 schedule
|
|
Message-ID: <20020413143539.7818bf7d.nconway@klamath.dyndns.org>
|
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In-Reply-To: <002301c1e2b3$804bd000$0200a8c0@SOL>
|
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References: <GNELIHDDFBOCMGBFGEFOGEBHCCAA.chriskl@familyhealth.com.au>
|
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<3CB52C54.4020507@freaky-namuh.com>
|
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<20020411115434.201ff92f.nconway@klamath.dyndns.org>
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<3CB61DAB.5010601@freaky-namuh.com>
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<24184.1018581907@sss.pgh.pa.us>
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<3CB65B49.93F2F790@tpf.co.jp>
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<20020412004134.5d35a2dd.nconway@klamath.dyndns.org>
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<20020412095116.B6370@zf.jcu.cz>
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<27235.1018620866@sss.pgh.pa.us>
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<3CB70E7C.3090801@xythos.com>
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<002301c1e2b3$804bd000$0200a8c0@SOL>
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X-Mailer: Sylpheed version 0.7.4 (GTK+ 1.2.10; i386-debian-linux-gnu)
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Status: OR
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On Sat, 13 Apr 2002 14:21:50 +0800
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"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> wrote:
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> Could this cache mechanism be used to make views fast as well?
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The current PREPARE/EXECUTE code will speed up queries that use
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rules of any kind, including views: the query plan is cached after
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it has been rewritten as necessary, so (AFAIK) this should mean
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that rules will be evaluated once when the query is PREPAREd, and
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then cached for subsequent EXECUTE commands.
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Cheers,
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Neil
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--
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Neil Conway <neilconway@rogers.com>
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PGP Key ID: DB3C29FC
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From pgsql-hackers-owner+M21309@postgresql.org Sun Apr 14 15:22:44 2002
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Return-path: <pgsql-hackers-owner+M21309@postgresql.org>
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Sun, 14 Apr 2002 21:21:44 +0200
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Date: Sun, 14 Apr 2002 21:21:44 +0200
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From: Karel Zak <zakkr@zf.jcu.cz>
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To: Tom Lane <tgl@sss.pgh.pa.us>
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cc: Bruce Momjian <pgman@candle.pha.pa.us>, pgsql-hackers@postgresql.org,
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Neil Conway <nconway@klamath.dyndns.org>
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Subject: Re: [HACKERS] 7.3 schedule
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Message-ID: <20020414212144.A12196@zf.jcu.cz>
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References: <200204121621.g3CGL4310492@candle.pha.pa.us> <27964.1018630286@sss.pgh.pa.us>
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In-Reply-To: <27964.1018630286@sss.pgh.pa.us>; from tgl@sss.pgh.pa.us on Fri, Apr 12, 2002 at 12:51:26PM -0400
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Precedence: bulk
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Status: OR
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On Fri, Apr 12, 2002 at 12:51:26PM -0400, Tom Lane wrote:
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> Bruce Momjian <pgman@candle.pha.pa.us> writes:
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> > Certainly a shared cache would be good for apps that connect to issue a
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> > single query frequently. In such cases, there would be no local cache
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> > to use.
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>
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> We have enough other problems with the single-query-per-connection
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> scenario that I see no reason to believe that a shared plan cache will
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> help materially. The correct answer for those folks will *always* be
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> to find a way to reuse the connection.
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My query cache was write for 7.0. If some next release will use
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pre-forked backend and after a client disconnection the backend will
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still alives and waits for new client the shared cache is (maybe:-) not
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needful. The current backend fork model is killer of all possible
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caching.
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We have more caches. I hope persistent backend help will help to all
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and I'm sure that speed will grow up with persistent backend and
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persistent caches without shared memory usage. There I can agree with
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Tom :-)
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Karel
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--
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Karel Zak <zakkr@zf.jcu.cz>
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http://home.zf.jcu.cz/~zakkr/
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C, PostgreSQL, PHP, WWW, http://docs.linux.cz, http://mape.jcu.cz
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TIP 4: Don't 'kill -9' the postmaster
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From pgsql-hackers-owner+M21321@postgresql.org Sun Apr 14 20:40:08 2002
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Return-path: <pgsql-hackers-owner+M21321@postgresql.org>
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X-Authentication-Warning: localhost.localdomain: camber owned process doing -bs
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Date: Sun, 14 Apr 2002 20:38:48 -0400 (EDT)
|
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From: Brian Bruns <camber@ais.org>
|
|
X-X-Sender: <camber@localhost.localdomain>
|
|
To: Hannu Krosing <hannu@tm.ee>
|
|
cc: <pgsql-hackers@postgresql.org>
|
|
Subject: Re: [HACKERS] 7.3 schedule
|
|
In-Reply-To: <1018704763.1784.1.camel@taru.tm.ee>
|
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Message-ID: <Pine.LNX.4.33.0204142027180.9523-100000@localhost.localdomain>
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Status: OR
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|
|
On 13 Apr 2002, Hannu Krosing wrote:
|
|
|
|
> On Fri, 2002-04-12 at 03:04, Brian Bruns wrote:
|
|
> > On 11 Apr 2002, Hannu Krosing wrote:
|
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> >
|
|
> > > IIRC someone started work on modularising the network-related parts with
|
|
> > > a goal of supporting DRDA (DB2 protocol) and others in future.
|
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> >
|
|
> > That was me, although I've been bogged down lately, and haven't been able
|
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> > to get back to it.
|
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>
|
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> Has any of your modularisation work got into CVS yet ?
|
|
|
|
No, Bruce didn't like the way I did certain things, and had some qualms
|
|
about the value of supporting multiple wire protocols IIRC. Plus the
|
|
patch was not really ready for primetime yet.
|
|
|
|
I'm hoping to get back to it soon and sync it with the latest CVS, and
|
|
clean up the odds and ends.
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|
|
|
> > DRDA, btw, is not just a DB2 protocol but an opengroup
|
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> > spec that hopefully will someday be *the* standard on the wire database
|
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> > protocol. DRDA handles prepare/execute and is completely binary in
|
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> > representation, among other advantages.
|
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>
|
|
> What about extensibility - is there some predefined way of adding new
|
|
> types ?
|
|
|
|
Not really, there is some ongoing standards activity adding some new
|
|
features. The list of supported types is pretty impressive, anything in
|
|
particular you are looking for?
|
|
|
|
> Also, does it handle NOTIFY ?
|
|
|
|
I don't know the answer to this. The spec is pretty huge, so it may, but
|
|
I haven't seen it.
|
|
|
|
Even if it is supported as a secondary protocol, I believe there is alot
|
|
of value in having a single database protocol standard. (why else would I
|
|
be doing it!). I'm also looking into what it will take to do the same for
|
|
MySQL and Firebird. Hopefully they will be receptive to the idea as well.
|
|
|
|
> ----------------
|
|
> Hannu
|
|
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|
Cheers,
|
|
|
|
Brian
|
|
|
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