I recently installed a trial version of Interbase on a development server that includes a nifty tool that allows me to monitor, among other things, the number of active connections to my server. After playing with this feature briefly, I noticed that SEVERAL connections are opened between my web server and the database. At first, I thought this was a little weird because I use the ibase_pconnect() function to establish communication with my database, and I expected to see only 1 connection. However, after doing some reading, I discovered that this behavior is probably by design - the result of Apache spawning several child processes, each one establishing its own persistent connection(s) to the database.
What I am baffled by is the fact that the total nunber of connections between the web server and my database seems to max out at 9. Why 9? Not that I have a problem with this number. I just want to understand how this limit was reached so that I might predict how the application will perform in a production capacity.
I can't think of a reason it would max out at 9 other than perhaps you really don't have more than 9 connections open. My understanding is that Apache will open a connection per child, per database connection where a connection is made up of the host, user, and database.
How many apache processes are running when you take this measurement? There's no gaurantee that each of them will have hit your web app and start up there own connection.
You might use something like ab (apache benchmark) to hit a page that initiates a persistent connection to see what happens as the number of apache processes grows.
I have checked my Apache config (httpd.conf) file, and as far as I can tell, the maximum number of child processes is set to 20. So again I ask: why does the number of connections max out at 9? Shouldn't they max out at 20 or 21 (1 parent + 20 children)?
Not necessarily (see above). It could very well be that for 20 children you could have *more* than that number of connections if your web pages connect to multiple databases...
And finally, I have noticed that the connections, once established, NEVER expire. I realize that this is sort of the point with persistent connections, but I was curious whether persistent connections are ever terminated or recycled.
I don't think so. I suppose the database could kill lingering connections... I don't know about that.
What I've done in the past is to set the number of requests each apache child is allowed to serve to some number that will be reached on some reasonable frequency. Then it closes that child which closes the connections...
Any explanations/impressions would be appreciated.
Mike
FYI... My php.ini file is set to allow unlimited connections/unlimited persistent connections. Also, the trial license of the database I am testing claims to be limited to 1 client, and the only client accessing the database is my web app. Just thought I'd mention that as I don't think the number of connections has any direct correlation to the client license.
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