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.\" This is -*-nroff-*-
.\" XXX standard disclaimer belongs here....
.\" $Header: /cvsroot/pgsql/src/man/Attic/lock.l,v 1.1 1998/01/23 06:01:36 momjian Exp $
.TH FETCH SQL 01/23/93 PostgreSQL PostgreSQL
.SH NAME
lock - exclusive lock a table
.SH SYNOPSIS
.nf
\fBlock\fR classname
.fi
.SH DESCRIPTION
.BR lock
exclusive locks a table inside a transaction. The classic use for this
is the case where you want to \fBselect\fP some data, then update it
inside a transaction. If you don't exclusive lock the table before the
\fBselect\fP, some other user may also read the selected data, and try
and do their own \fBupdate\fP, causing a deadlock while you both wait
for the other to release the \fBselect\fP-induced shared lock so you can
get an exclusive lock to do the \fBupdate.\fP
.SH EXAMPLES
.nf
--
-- Proper locking to prevent deadlock
--
begin work;
lock mytable;
select * from mytable;
update mytable set (x = 100);
end work;
.SH "SEE ALSO"
begin(l),
end(l),
select(l).
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