Resolution:
Description:
========
On a Linux environment, why do we see that the physical memory usage is approaching to 100% even when the running BW engine does not use much memory?

Environment:
=========
Linux

Symptoms:
========
On a Linux box, you may only have one BW engine with heap size set to 1GB while the total physical memory is much larger, such as 4GB or even 8GB. However, when running the "top" or "free" command to check the available system memory, it sometimes shows that the physical memory usage is near to 100%.


Cause:
=====
This has nothing to do with the BW engine. Linux is borrowing unused memory for disk caching. This makes it looks like you are low on memory.

Resolution:
=======
Linux will count the memory that is used for disk caching as "used". If your applications needs more memory, just take back a chunk that the disk cache borrowed. The disk cache can always be given back to applications immediately and automatically. To see how much memory is free to use for your applications, run "free -m" and look at the row that says "-/+ buffers/cache" in the column that says "free". The answer is in megabytes

$ free -m
             total       used       free     shared    buffers     cached
Mem:          1504       1491         13          0         91        764
-/+ buffers/cache:        635        869
Swap:         2047          6       2041
$

If you do n'o know how to read the numbers, you will think memory usage is 99% (1491/1504) full when really it is just 42% = 635/1504.