Do you need to unlock the table fifo when you are done? On Fri, 2002-11-01 at 11:51, Tom Lane wrote: > Chris Gamache <[EMAIL PROTECTED]> writes: > > I have a program that claims a row for itself > > > my $processid = $$; > > my $sql_update = <<EOS; > > UPDATE fifo > > set status=$processid > > WHERE id = (SELECT min(id) FROM fifo WHERE status=0); > > EOS > > > The problem occurrs when two of the processes grab the exact same row at the > > exact same instant. > > Probably the best fix is to do it this way: > > BEGIN; > LOCK TABLE fifo IN EXCLUSIVE MODE; > UPDATE ... as above ... > COMMIT; > > The exclusive lock will ensure that only one process claims a row > at a time (while not preventing concurrent SELECTs from the table). > This way you don't need to worry about retrying. > > regards, tom lane > > ---------------------------(end of broadcast)--------------------------- > TIP 6: Have you searched our list archives? > > http://archives.postgresql.org -- Wei Weng <[EMAIL PROTECTED]>
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