Re: Need help in performance tuning.

On Fri, 9 Jul 2010, Kevin Grittner wrote:
> Any thoughts on the "minimalist" solution I suggested a couple weeks
> ago?:
>
> http://archives.postgresql.org/pgsql-hackers/2010-06/msg01385.php
> http://archives.postgresql.org/pgsql-hackers/2010-06/msg01387.php
>
> So far, there has been no comment by anyone....

Interesting idea. As far as I can see, you are suggesting solving the too
many connections problem by allowing lots of connections, but only
allowing a certain number to do anything at a time?

A proper connection pool provides the following advantages over this:

1. Pool can be on a separate machine or machines, spreading load.
2. Pool has a lightweight footprint per connection, whereas Postgres
doesn't.
3. A large amount of the overhead is sometimes connection setup, which
this would not solve. A pool has cheap setup.
4. This could cause Postgres backends to be holding onto large amounts of
memory while being prevented from doing anything, which is a bad use of
resources.
5. A fair amount of the overhead is caused by context-switching between
backends. The more backends, the less useful any CPU caches.
6. There are some internal workings of Postgres that involve keeping all
the backends informed about something going on. The more backends, the
greater this overhead is. (This was pretty bad with the sinval queue
overflowing a while back, but a bit better now. It still causes some
overhead).
7. That lock would have a metric *($!-load of contention.

Matthew

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