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To: Joseph Shraibman <jks@selectacast.net>
cc: "pgsql-general@hub.org" <pgsql-general@hub.org>
Subject: Re: select for update not locking properly. 
In-reply-to: <396D2AEA.5D19984A@selectacast.net> 
References: <396D2AEA.5D19984A@selectacast.net>
Comments: In-reply-to Joseph Shraibman <jks@selectacast.net>
	message dated "Wed, 12 Jul 2000 22:35:22 -0400"
Date: Thu, 13 Jul 2000 03:34:20 -0400
Message-ID: <28676.963473660@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
X-Archive-Number: 200007/555

Joseph Shraibman <jks@selectacast.net> writes:
> But the locking isn't working properly.  I do something that should
> cause 3 different threads to try and do that append, and the first one
> goes through properly, but the second two append to the result of the
> first on only, meaning that the third one didn't see the result of the
> second's append.

Can't duplicate it here.  I did:

<in psql window 1>

regression=# create table mytable(mystring text, x int, y int);
CREATE
regression=# insert into mytable values('z',1,4);
INSERT 399867 1
regression=# insert into mytable values('foo',3,4);
INSERT 399868 1
regression=# begin;
BEGIN
regression=# SELECT mystring FROM mytable WHERE x = 3 AND y = 4 FOR UPDATE;
 mystring
----------
 foo
(1 row)

<in psql window 2>

regression=# begin;
BEGIN
regression=# SELECT mystring FROM mytable WHERE x = 3 AND y = 4 FOR UPDATE;
[ psql hangs ]

<in psql window 3>

regression=# begin;
BEGIN
regression=# SELECT mystring FROM mytable WHERE x = 3 AND y = 4 FOR UPDATE;
[ psql hangs ]

<back to psql window 1>

regression=# UPDATE mytable SET mystring = 'foo bar' WHERE x = 3 AND y = 4;
UPDATE 1
regression=# end;
COMMIT
regression=#

<psql window 3 now responds>

 mystring
----------
 foo bar
(1 row)

regression=# UPDATE mytable SET mystring = 'foo bar baz' WHERE x = 3 AND y = 4;
UPDATE 1
regression=# end;
COMMIT
regression=#

<psql window 2 now responds>

  mystring
-------------
 foo bar baz
(1 row)

regression=#

Looks pretty cool to me...

			regards, tom lane