Re: Clarification reqeusted for "select * from a huge table"

Gokulakannan Somasundaram wrote:
> Hi,
> I had a chance to test one of the real world cases with Oracle and
> PostgreSQL. Create a Table with 10 million rows (i worked on a 1GB RAM
> machine) both in oracle and Postgresql. Just write a JDBC program for
> a 'select *' on that table. With PostgreSQL as backend, java crashes
> saying that it has met 'Out Of Memory'. With Oracle it doesn't.
> Postgres tried to send all the results back to the client at one
> shot, whereas in Oracle it works like a Cursor. Is this issue already
> well known among hackers community? If known, why is it designed this
> way?

It returns everything because you've asked for it. If you wanted
something that looks like a cursor, PG assumes you'll request a cursor.

As to why, there are two reasons:
1. It's always been that way and changing it now would irritate most of
the existing user-base.
2. Repeat your test with 5,10,50,100 clients all running different big
queries and see which puts a greater load on the server. PG favours
supporting lots of clients by pushing the load onto them.

> I also noticed that it doesn't crash with psql, but it takes a
> long time to show the first set of records. It takes a long time, even
> to quit after i pressed 'q'.
> With oracle SQLPlus, it is quite instantaneous.

Again, you're measuring different things. What is the time to the *last*
row?

--
Richard Huxton
Archonet Ltd