On Thu, 24 Feb 2005 10:26:58 +0800, Derek Fountain <nospam@example.com> wrote:
[color=blue]
>For a low-ish traffic website that is doing the simple "build pages from
>HTML templates and info in a database" kind of thing, do the wise folks in
>this newsgroup advocate connecting and disconnecting from the DB with each
>query, or maintaining a persistent connection in the session?
>
>I guess my application could work either way, and I've gravitated towards
>the connect-query-disconnect method, but not for any really good reason. It
>struck me as simpler to stick with the stateless way of doing it. The only
>obvious drawback I can see is the performance penalty, which I guess could
>be large if the website gets busy.
>
>What do other people think? Is there an obvious best practise on the merits,
>or is it down to the application and developer?[/color]
It Depends (tm) on how many distinct connections you use, where a connection
is defined by both the database and the username.
If all your applications on the server use a small set of user credentials
against a small set or one database, then persistent connections are great,
particularly for databases where connection is not particularly cheap (e.g.
Oracle).
If you access more than a small number of distinct username/database
combinations, persistent connections can be disastrous, as over time each
webserver child process will each build up a pool of connections to each of the
username/database combinations and hold them open.
I consider the fact that PHP's persistent database connection infrastructure
doesn't include a "disconnect after X seconds" feature a fairly nasty flaw -
surely you'd want your pool of connections to form a common working set of
connections, rather than holding open connections for eternity. This can
probably be mitigated by webservers' methods of recycling child processes;
MaxRequestsPerChild in Apache, or the equivalent methods of recycling worker
processes in IIS6, but this seems to be the wrong level to do this.
--
Andy Hassall / <andy@andyh.co.uk> / <http://www.andyh.co.uk>
<http://www.andyhsoftware.co.uk/space> Space: disk usage analysis tool
