Mark,
I don't know how it will exactly works in postgres but my expectations are:
Mark Woodward wrote:
Is there a difference in PostgreSQL performance between these two
different strategies:
if(!exec("update foo set bar='blahblah' where name = 'xx'"))
exec("insert into foo(name, bar) values('xx','blahblah'");
or
The update code generates new tuple in the datafile and pointer has been
changed in the indexfile to the new version of tuple. This action does
not generate B-Tree structure changes. If update falls than insert
command creates new tuple in the datafile and it adds new item into
B-Tree. It should be generate B-Tree node split.
exec("delete from foo where name = 'xx'");
exec("insert into foo(name, bar) values('xx','blahblah'");
Both commands should generate B-Tree structure modification.
I expect that first variant is better, but It should depend on many
others things - for examples triggers, other indexes ...
REPLACE/UPSERT command solves this problem, but It is still in the TODO
list.
Zdenek
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