On Tue, 2002-06-18 at 10:36, Josh Berkus wrote:
> John,
>
> > I'm optimising my data load by dropping indexes.
> >
> > My question is, what do I do with the indexes created by postgres for
> > primary keys ?
> >
> > Is it OK to drop them ?
>
> No.
I've done it many times...
alter table t_lane_tx
add constraint c_lane_tx_pk primary key (lane_tx_id);
> > How do I create them again afterwards, so that they are used
> > correctly for constraint checking ?
In this instance, you can have speed or you can have correctness.
Pick one. Of course, if you know that your input data is good,
you have both...
> I'm not sure that it's possible to add a primary key to an existing
> populated table.
See above.
> I'd reccommend instead dropping all other indexes but the primary key.
> It's just not a good idea. How much is this slowing down the data
> load? Can you do a comparison test on a keyed vs. keyless table?
Ack! Have you tried loading millions of rows to an indexed table?
Imagine, if you will, a 1MHz 8080 writing to a floppy drive...
> FYI, in 7.4 or 8.0 we will have DEFERRABLE UNIQUE constraints, which
> means that it may be possible for you to hold the PK checking until the
> data load is finished, adding some speed to the process.
Still, I bet that creating an (implicit or explicit) index would
be faster if you are loading the data in bite-sized chunks.
--
+-------------------------------------------------------------+
| Ron Johnson, Jr. Home: ron.l.johnson@cox.net |
| Jefferson, LA USA http://ronandheather.dhs.org:81 |
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| "Object-oriented programming is an exceptionally bad idea |
| which could only have originated in California." |
| --Edsger Dijkstra |
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