On Sat, Apr 24, 2010 at 4:46 PM, Andre Lopes <lopes80andre@xxxxxxxxx> wrote: > I need to do a SELECT and an UPDATE, but I will have concurrent processes > doing the same task. > > How can I prevent that the concurrent task don't have the same results in > the SELECT? Locking a table? How can I do that? It sounds like you might be looking for SELECT ... FOR UPDATE, see: http://www.postgresql.org/docs/current/static/sql-select.html Basically, you could have each transaction issue SELECT ... FOR UPDATE for rows intended to be updated later. Only one transaction would be able to acquire the necessary locks for the same rows at the same time; the other transaction(s) would block until the locks are released by the first transaction's commit, and then would see the new values. This paragraph assumes you're using the default "read committed" transaction isolation level, you might want to read more at: http://www.postgresql.org/docs/current/static/transaction-iso.html And if you really want to know about full table locking, you can read more at: http://www.postgresql.org/docs/current/static/sql-lock.html though it doesn't sound like you'll actually need full table locks. Josh -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
