| From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | josh(at)agliodbs(dot)com, pgsql-hackers(at)postgresql(dot)org, Jaime Casanova <systemguards(at)gmail(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net> |
| Subject: | Re: MERGE vs REPLACE |
| Date: | 2005-11-16 00:16:21 |
| Message-ID: | 200511160016.jAG0GLa11084@candle.pha.pa.us |
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| Lists: | pgsql-hackers |
Tom Lane wrote:
> Josh Berkus <josh(at)agliodbs(dot)com> writes:
> > But even REPLACE requires predicate locking. There's no real way to get
> > around it.
>
> The point though is that REPLACE is restricted to a type of predicate
> narrow enough to be enforced through a unique-index mechanism, and so
> it's implementable without solving the general case of predicate
> locking.
>
> Predicate locking for narrow cases isn't very hard; it's the general
> case of arbitrary predicates that's hard.
My feeling is we should implement MERGE for the limited cases we can,
and throw an error for cases we can not (or require table locking), and
then see what reports we get from users.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
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