| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
| Cc: | Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Bruno Wolff III <bruno(at)wolff(dot)to>, Peter Eisentraut <peter_e(at)gmx(dot)net>, pgsql-hackers(at)postgresql(dot)org, Josh Berkus <josh(at)agliodbs(dot)com>, Jaime Casanova <systemguards(at)gmail(dot)com> |
| Subject: | Re: someone working to add merge? |
| Date: | 2005-11-15 14:27:56 |
| Message-ID: | 10365.1132064876@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> This only happens because of the unique index. There's no predicate
> locking involved. The btree code goes some lengths to make this work;
That's one way to look at it; the other is to say that we have predicate
locking for a very specific class of predicate, ie, equality of a
unique key.
In practice I think we only have a useful lock there for *primary* keys,
because unique without NOT NULL doesn't actually constrain you to just
one matching row ...
regards, tom lane
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