| From: | "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com> |
|---|---|
| To: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
| Cc: | mark(at)mark(dot)mielke(dot)cc, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Martijn van Oosterhout <kleptog(at)svana(dot)org>, Zeugswetter Andreas DCP SD <ZeugswetterA(at)spardat(dot)at>, Dann Corbit <DCorbit(at)connx(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Rick Gigger <rick(at)alpinenetworking(dot)com>, Christopher Kings-Lynne <chriskl(at)familyhealth(dot)com(dot)au>, 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: | 2005-11-21 21:44:36 |
| Message-ID: | 20051121214436.GL19279@pervasive.com |
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| Lists: | pgsql-hackers |
On Thu, Nov 17, 2005 at 09:30:43PM -0500, Bruce Momjian wrote:
> > Is the requirement for predicate locking, over and above a unique
> > constraint on an index that involves the record key, to deal with
> > the scenario of two inserts executing at the same time, both before
> > commit?
>
> No. If you have a primary key you can easily prevent duplicates. You
> need a table lock or predicate locking to prevent duplicates if you do
> not have a primary key.
AFAIK you can also accomplish this without a table lock as long as you
have a unique index on the right set of fields and those fields are also
NOT NULL. ISTM it would be good to support that case as well, since you
might want to MERGE based on something other than the PK.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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