[EMAIL PROTECTED] (Stephan Szabo) writes: > On Tue, 28 Sep 2004, Randy Yates wrote: > >> Michael Fuhr <[EMAIL PROTECTED]> writes: >> >> > On Tue, Sep 28, 2004 at 01:30:08PM +0000, Randy Yates wrote: >> >> Randy Yates <[EMAIL PROTECTED]> writes: >> >> > >> >> > I'm confused. Where is the lock? Is it on the 1 record in the model table? >> > >> > Yes. >> > >> >> > If so, why is that record locked? Is it possible in Postgresql to update >> >> > the primary key of a record? >> > >> > When you insert a row that has a foreign key reference, PostgreSQL >> > does a SELECT FOR UPDATE on the referenced row in the foreign table; >> > the lock prevents other transactions from changing the referenced >> > row before this transaction completes. Unfortunately it also >> > prevents other transactions from acquiring a lock on the same row, >> > so those transactions will block until the transaction holding the >> > lock completes. >> >> Well, yeah - sure it does. Given that the locking mechanism's >> granularity is record-level, it MUST if it is to guarantee referential >> integrity. > > But it doesn't need to prevent other transactions that want to just see if > the row is there from continuing (as opposed to ones that want to actually > modify that row). We just simply don't have that lock currently.
I see the light. You mean it would be nice to be able to have a "LOCK-FOR-UPDATE-ONLY" lock as well as a "LOCK-FOR-UPDATE-OR-READ" lock, but all you have now is "LOCK-FOR-UPDATE-OR-READ" and that gets applied even when you don't care if someone else reads the record? -- % Randy Yates % "So now it's getting late, %% Fuquay-Varina, NC % and those who hesitate %%% 919-577-9882 % got no one..." %%%% <[EMAIL PROTECTED]> % 'Waterfall', *Face The Music*, ELO http://home.earthlink.net/~yatescr ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html
