| From: | Martijn van Oosterhout <kleptog(at)svana(dot)org> |
|---|---|
| To: | Dann Corbit <DCorbit(at)connx(dot)com> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>, Rick Gigger <rick(at)alpinenetworking(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>, "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>, 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 19:33:22 |
| Message-ID: | 20051116193322.GN31063@svana.org |
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| Lists: | pgsql-hackers |
On Wed, Nov 16, 2005 at 11:06:15AM -0800, Dann Corbit wrote:
> > -----Original Message-----
> > From: pgsql-hackers-owner(at)postgresql(dot)org [mailto:pgsql-hackers-
> > owner(at)postgresql(dot)org] On Behalf Of Simon Riggs
> > > Conceptually, a MERGE statement is just a long string of INSERTs and
> > > UPDATEs in the same transaction and I think we should treat it as
> > > such.
>
> Merge could also be considered as a long string of deletes and inserts.
> I guess that deleting those records that already exist and then
> inserting all of the records is faster because it could be done like a
> single join to perform the delete and then a single batch insert.
And for us it makes no difference because in MVCC, UPDATE == DELETE +
INSERT. IMHO it's just a nice construct to specify UPDATEs and INSERTs
in the same statement.
Have a nice day,
--
Martijn van Oosterhout <kleptog(at)svana(dot)org> http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.
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