how improve the php memory usage?

Hi,

I develop a PHP Live Chat app but this not work well in some hosting servers, the cause the memory usage.

Any tool for monitoring the memory usage of the process or for tunning my program in the PHP?

This is the info of memory usage:

memory usage :265,900 bytes
memory peak usage :272,940 bytes
memory end usage :265,976 bytes

My app works well in others servers but in my shared account don't works well because a his have a PHP limit. The php memory limit in my shared account is 64 .

I don't know if the memory limit 64 is 64 MB or 64 process ? What they mean with "php memory limit set at 64"?

Memory limit 64 is right or is a small value ?

Regards,
Peter