Releasing variables vs garbage collection

dcmbrown

I work in a PHP shop where common practice is to simply setup variables, file pointers, etc. Then let garbage collection take care of them once the script has ended.

In a number of online applications however, I have found that letting php garbage collection take care of releasing memory slows the script down significantly. As it happens many of these use either a huge number of variables or variables which take up a huge amount of memory. Using unset($var) speeds these up significantly!

So is letting scripts end and php garbage collection take place slow a script down or is my use of the unset() function which speeding up my scripts just in my imagination and coincidence and not the rule of thumb?

Weedpacket

If your data structures are large then yes, you should explicitly unset them when you're done with them. If you just wait for them to drift out of scope they could be sitting around for a long time hogging memory. Quite apart from the increased hassles with allocation memory for additional structures, as soon as the server starts having to swap memory out to disk, thins will slow way down.

liquorvicar

i've been mulling over a similar issue with DB query results but haven't found a definitive answer.

do i need to explictly drop a DB connection before exiting a script? or does the DB connection die when the script finshes? does this also apply when i exit with a header() command?
in a similar vein, should i always use mysql_free_result or does this happen automatically when a script finishes running?

Weedpacket

Originally posted by liquorvicar
i've been mulling over a similar issue with DB query results but haven't found a definitive answer.

See, e.g.,

[man]mysql_close[/man]
Using mysql_close() isn't usually necessary, as non-persistent open links are automatically closed at the end of the script's execution. See also freeing resources.