Re: Suggestion for optimization

-----Original Message-----
From: Doug McNaught [mailto:doug@wireboard.com]
Sent: Friday, April 05, 2002 11:30 AM
To: Dann Corbit
Cc: pgsql-hackers@postgresql.org
Subject: Re: [HACKERS] Suggestion for optimization


"Dann Corbit" <DCorbit@connx.com> writes:

> It would be nice if total table cardinality could be maintained live.
> So (after the initial vacuum) we update the cardinality for each table
> in the system table (or perhaps add an entry to the table itself).
> There are two reasons why this is an important optimization.  Firstly,
> it is a psychological benefit for both benchmarks and customers when
> doing a select count(*) from <tablename>.  This is something that pops
> up all the time in benchmarks and customers do it too, in order to get
a
> feel for speed.  By storing the current number and incrementing for
> every insert and decrementing for every delete, the count(*) case with
> no where clause can return the value instantly.

How would this work with MVCC?
>>
Whenever a commit occurs, the pending inserts are totaled into the sum
and the pending deletes are subtracted.  It can be a list in memory or
whatever.  Maybe you are referring to the old (expired) rows begin
stored until vacuum?  Perhaps I really don't understand your question or
the issues involved.  Why does MVCC complicate issues?
<<