Re: someone working to add merge?

Josh Berkus wrote:
> Funny, we were just discussing this at OpenDBCon.   Seems that you
> can't do a full implementation of MERGE without Predicate Locking
> (the ability to say "lock this table against inserts or updates of
> any row with key=5"). However, Peter suggested that we could do a
> proof-of-concept implementation, working out syntax and trigger
> issues, based on a full table lock and do the hard work once it was
> proved to be feasable.

Yes, I've started to work on this.  Realizing that the current way to 
manually do an UPDATE-else-INSERT or DELETE-then-INSERT involves a 
table lock anyway, a MERGE implementation using a table lock would at 
least give some convenience benefit to users. (And possibly some 
performance, too, if the decision logic is currently run in the 
client.)

A predicate locking implementation for MERGE might actually not be all 
that complicated, because you only need to look on pk = constant, not 
on arbitrary expressions.  Nevertheless, I think it's best to write the 
MERGE command first and then optimize the locking.

-- 
Peter Eisentraut
http://developer.postgresql.org/~petere/