From: | "Merlin Moncure" <merlin(dot)moncure(at)rcsonline(dot)com> |
---|---|
To: | "Thomas Rokohl" <rokohl(at)raygina(dot)de> |
Cc: | <pgsql-odbc(at)postgresql(dot)org> |
Subject: | Re: lock - feedback |
Date: | 2005-10-12 14:18:32 |
Message-ID: | 6EE64EF3AB31D5448D0007DD34EEB3417DD591@Herge.rcsinc.local |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-odbc |
> > Have you looked at contrib\userlock? With it, you can simulate
> > pessimistic locks with a non-blocking result code.
> >
> > Merlin
> >
> >
> >
> contrib/userlock? where i can find something about this? in the manual
i
http://developer.postgresql.org/cvsweb.cgi/~checkout~/pgsql/contrib/user
lock/README.user_locks?rev=1.3;content-type=text%2Fplain
> can't find something ?!?!
> mhm what is with the "lost update" problem, can i solve it with it?!?!
probably. However, in many cases proper use of transactions is more
appropriate. This will be even easier to do when we get proper
assertions.
> i can't visualize how it can works?
select user_write_lock(oid) from my_table where value = x;
returns 1 on success, 0 on failure.
just be careful...
select user_write_lock(oid) from my_table where value = x order by y
limit 1;
can acquire more locks than you might think since the table has to be
materialized to do the order.
better to write:
select user_write_lock(oid) from
(
select oid, * from my_table where value = x order by y limit 1;
)
also, don't use oid :). In my applications, I make a domain type called
'cuid' which pulls nextval() from a public sequence. Put that into your
tables and lock on it. Just watch for dump/restore.
Merlin
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