chris said:
Time. Opening a db connection is time consuming. There are many levels involved (making the connection, authentication, etc).. Even worse if the connection is over tcp/ip because that overhead comes in on top as well.
I replied:
Have you timed it? Maybe I'll do that tomorrow.
Okay, I performed a test that made 100 queries, and found that it took about four times as long to open a dB connection each time and get the data as it did to open it once. In other words, if your script pulls data from a dB 100 times, then making a connection to the dB once, pulling the data, and then closing the dB is four times as fast as opening the dB, pulling the data, and closing the dB in sequence one hundred times.
Now, that sounds like you should open your dB at the start of your script and just leave it open until the your script quits (as the original poster suggested), but there's a few thing to consider here.
1. The total time difference shown in the above test is a little over a tenth of a second.
2. By keeping the dB open, you're actually tying up the resources of the server more than necessary. After all, your script will always run longer than the query, right?
3. Most scripts (I'm guess here) don't access the dB 100 times or more -- so doing is less, means less of a difference.
4. And lastly, by closing the dB in your script when you're done with it, allows the server to use it's resources to "clean-up" quicker and have more time to be responsive to other queries.
So, not that you implied otherwise, I still don't see any convincing argument as to why one should open a dB at the start of a script and not close it as the original poster asked. Furthermore, not that I'm anyone special, but if I was overlooking someone's code who did that, I wouldn't think favorably of the technique -- it would appear as sloppy programming to me.
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