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I have a few time-consuming and (potentially) memory-intensive functions in my LAMP web application. Most of these functions will be executed every minute via cron (in some cases, the cron job will execute multiple instances of these functions).
Since memory is finite, I don't want to run into issues where I am trying to execute a function the environment can no longer handle. What is a good approach at dealing with potential memory problems?
I'm guessing that I need to determine how much memory is available to me, how much memory each function requires before executing it, determine what other functions are being executed by the cron AND their memory usage, etc.
Also, I don't want to run into the issue where a certain function somehow gets execution priority over other functions. If any priority is given, I'd like to have control over that somehow.
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PHP memory management functions are invoked by the MySQL Native Driver through a lightweight wrapper. Among others, the wrapper makes debugging easier. The various MySQL Server and the various client APIs differentiate between buffered and unbuffered result sets.
The memory_get_usage function can be used to track the memory usage. The 'malloc' function is not used for every block required, instead a big chunk of system memory is allocated and the environment variable is changed and managed internally.
You should set your PHP memory limit as low as you can while still allowing your site to function normally. 128 MB is a good baseline. That's a decent amount of memory that will take care of most intensive plugins. If you know you're going to need some extra power, 256 MB will cover even the heaviest plugins.
The default memory limit is 256M and this is usually more than sufficient for most needs. If you need to raise this limit, you must create a phprc file.
you could look into caching technologies like APC which lets you write stuff right into the RAM so that you can access it fast which of use if you dont want to do expensive tasks like mysql queries repeatedly.
an example for caching i could think of would be that you could cache emails rather than retreiving them again and again from the email server. basicaly ram caching is a very useful technique if you have things in your script that you want to preserve for the next time of script execution but if your script does unique things every time it is executed it would be useless. also as for contoll you could call memory_get_usage() on each script execution and write that value into the apc cache so that every cron could retreive that value and look whether enough memory is free for it to complete.
as for average usage you could write an array with the last lets say 100 function executions and when you call that function again it could apc_fetch that from the ram and calculate the average memory usage for that function then compare it to how much ram is being used right now and then decide wheter to start. furthermore it could write that estimate into the current memory usage variable to prevent other scripts from being run. at the end of that function you subtract that amount from the variable again. tl;dr: look into the apc_fetch, apc_store and memory_get_usage functions
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