Re: Suggestion for optimization

-----Original Message-----
From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
Sent: Friday, April 05, 2002 11:37 AM
To: Doug McNaught
Cc: Dann Corbit; pgsql-hackers(at)postgresql(dot)org
Subject: Re: [HACKERS] Suggestion for optimization

Doug McNaught <doug(at)wireboard(dot)com> writes:
> "Dann Corbit" <DCorbit(at)connx(dot)com> writes:
>> It would be nice if total table cardinality could be maintained live.

> How would this work with MVCC?

It wouldn't. That's why it's not there. Under MVCC, table cardinality
is in the eye of the beholder...
>>-------------------------
If this is true (even after a commit) then MVCC is a very bad thing. No
transactions occur, and two people ask the same question yet get
different answers. Doesn't that scare anyone? That would mean (among
other things) that Postgresql cannot be used for a data warehouse.

One of the primary facets of a reliable database transaction system is
repeatability. In fact, if there is no certain cardinality known after
commits, then there are no reliable database operations that can be
trusted.

How many accounts are 90 days overdue? Bill says 78 and Frank says 82.
Who is right and how can we know?

I have spent months working on Postgresql projects here (at CONNX
Solutions Inc.) and talked management into using an open source
database. Please tell me I'm not going to look like a bloody idiot in
the near term.
<<-------------------------