From: | Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com> |
---|---|
To: | "pgsql-novice(at)postgresql(dot)org" <pgsql-novice(at)postgresql(dot)org> |
Subject: | Transactional issue that begs for explanation |
Date: | 2010-09-10 08:49:46 |
Message-ID: | 4C89F12A.3000005@vmsinfo.com |
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Thread: | |
Lists: | pgsql-novice |
I am having problems explaining the following course of events:
I created table test_keys(key int,val varchar(10)); No PK, no indexes.
I populated the table using the following SQL:
insert into test_keys values(1,'Key1');
insert into test_keys values(2,'Key2');
insert into test_keys values(3,'Key3');
insert into test_keys values(4,'Key4');
insert into test_keys values(5,'Key5');
insert into test_keys values(6,'Key6');
insert into test_keys values(7,'Key7');
insert into test_keys values(8,'Key8');
insert into test_keys values(9,'Key9');
insert into test_keys values(10,'Key10');
insert into test_keys values(11,'Key11');
insert into test_keys values(12,'Key12');
insert into test_keys values(13,'Key13');
insert into test_keys values(14,'Key14');
insert into test_keys values(15,'Key15');
insert into test_keys values(16,'Key16');
insert into test_keys values(17,'Key17');
insert into test_keys values(18,'Key18');
insert into test_keys values(19,'Key19');
insert into test_keys values(20,'Key20');
To make the story more interesting, I added the following:
CREATE or REPLACE FUNCTION logtrg() RETURNS trigger AS $$
open(STDOUT,">>/tmp/logfile") or die("Cannot open log:$!\n");
$key=$_TD->{old}{key};
$val=$_TD->{old}{val};
print "Firing on: $key $val\n";
return;
$$ LANGUAGE plperlu;
CREATE TRIGGER log_upd BEFORE UPDATE on test_keys
FOR EACH ROW EXECUTE PROCEDURE logtrg();
Essentially, I added trigger that records the values that the trigger
fires upon and puts those values into /tmp/logfile
Next, opened 2 sessions and executed the following:
Session 1: Session 2:
----------------
----------------
begin; begin;
update test_keys update test_keys
set val='EVEN' set val='DIV5'
where key%2=0; where key%5=0;
rollback; commit;
Here is the content of my logfile:
root(at)ubuntu:~# tail -f /tmp/logfile
Firing on: 2 Key2
Firing on: 4 Key4
Firing on: 6 Key6
Firing on: 8 Key8
Firing on: 10 Key10
Firing on: 12 Key12
Firing on: 14 Key14
Firing on: 16 Key16
Firing on: 18 Key18
Firing on: 20 EVEN
Firing on: 5 Key5
Firing on: 10 Key10
Firing on: 15 Key15
Question: where did "EVEN" on the key 20 come from? The first
transaction was rolled back, the 2nd transaction shouldn't have seen any
changes made by the first transaction. I am using PgSQL 8.4.4 on Ubuntu
10, 32bit version (laptop).
I repeated the experiment several times, and this happens rather
consistently.
--
Mladen Gogala
Sr. Oracle DBA
1500 Broadway
New York, NY 10036
(212) 329-5251
www.vmsinfo.com
The Leader in integrated Media Intelligence Solutions
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