“致命错误：x字节允许的内存大小耗尽（试图分配y字节）”的含义“？

Question

(This is a very frequent error, but couldn't find the meaning.)

Fatal error: Allowed memory size of x bytes exhausted (tried to allocate y bytes)

I have some questions:

1. This is obviously an out-of-memory error, but what does it means in Layman's terms?
2. Is it possible to know some information (like server's RAM) from x?
3. What about y? Sometimes it is a two-digits number.

Thanks.

Answer 1

1. It means that the memory used by the PHP script exceeded the value of the memory_limit configuration option. Note this may or may not agree with what the operating system thinks the memory usage of the script is at the time of the error.
2. x gives you the value of the memory_limit configuration option. You can also assume that the server has at least enough virtual memory to handle the limit, but that's about it.
3. No, y is just the size of the straw that finally broke the camel's back.