On Dec 16, 2007 12:21 AM, <andrew@pillette.com> wrote:
> Loïc Marteau <okparanoid@free.fr> wrote ..
> > Steve Crawford wrote:
> > > If this
> > > is correct, I'd first investigate simply loading the csv data into a
> > > temporary table, creating appropriate indexes, and running a single
> > > query to update your other table.
>
> My experience is that this is MUCH faster. My predecessor in my current position was doing an update from a csv file
lineby line with perl. That is one reason he is my predecessor. Performance did not justify continuing his contract.
>
> > i can try this. The problem is that i have to make an insert if the
> > update don't have affect a rows (the rows don't exist yet). The number
> > of rows affected by insert is minor regards to the numbers of updated
> > rows and was 0 when i test my script). I can do with a temporary table
> > : update all the possible rows and then insert the rows that are in
> > temporary table and not in the production table with a 'not in'
> > statement. is this a correct way ?
>
> That's what I did at first, but later I found better performance with a TRIGGER on the permanent table that deletes
thetarget of an UPDATE, if any, before the UPDATE. That's what PG does anyway, and now I can do the entire UPDATE in
onecommand.
that's very clever, and probably is the fastest/best way to do it.
you can even temporarily add the trigger a transaction...I am going to
try this out in a couple of things (I currently do these type of
things in two statements) and see how it turns out.
merlin