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I was approached that in one of the system, there was an alert displaying in the custom dashboard

saying that there was low memory free available in the CS (ASCS01 server (distributed production

system).

Since the CS (Central Service System) ASCS01 contains only two services : message service and

Enqueue service; there will be never  much RAM memory utilization takes place.

Hence decided to investigate whether there was indeed almost 98% RAM memory utilization takes

place ? The explanation and procedure is described below

 

As it is only ASCS system i.e. Central Service system where enqueue and message services

installed, total RAM memory capacity = 4GB is sufficient.

 

As shown in the above, out of total Physical RAM memory 4211792K, 4085616K is used i.e. almost

98% utilized. That means it looks like less memory available but actually not. The reason is given

explanation below

Execute “Free -m”  command at root level  as shown in the figure below

 

 

Memory 2570M (i.e. 2.5GB) is actually free and 1542 Mb i.e. 1.5GB is used by application.

The reason is that out of the total amount of available memory is 4113M (i.e. 4GB), 1542M are used

by processes and 2570 Mb are free.

Linux is borrowing unused memory for disk caching. This makes it looks like that there is low on

memory, but really it is not ! Everything is fine!

Disk caching makes the system much faster! It does not take memory away from applications in any

way, ever!

 

If your applications want more memory, then disk cache can always be given back to applications

immediately! Thus there is no low on RAM.

 

If more memory is needed by programs , then Linux will free up the buffers and cache to yield

memory for the applications.

 

When an application processes not requires any more memory , then unused memory will return

back to Filesystems or disk cache.

 

As per Linux memory Architecture, 90% of Unused free RAM goes to Buffers / Disk Cache /

Filesystems Cached.

Conclusion:

This is applicable for all systems including standalone Database system or CI+CS+DB etc.

Despite showing 98% memory utilization; actual memory utilization as shown in the command Free

-m (second line in “used” column) is less utilized and has more memory available as shown

in the “free” column of second line.

 

Refer to website :

http://www.linuxatemyram.com/

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  1. Matt Fraser

    Hi Prasad,

    Good work, but you might want to adjust the tagging on this and your companion article (https://blogs.sap.com/2017/01/26/ram-memory-utilization-part-2-2/). I don’t think you’re writing about the NetWeaver Administrator tool for managing AS Java systems. Instead, much of what you’re describing here is really about managing Linux operating systems, so you should probably choose from among the three different Linux options for your primary tag, and perhaps put either “SAP NetWeaver Application Server” or perhaps “SAP NetWeaver Application Server for Java” in as a secondary tag. I would do this for you, but I’m not sure which variant of Linux you are writing about (or whether it matters), and there isn’t just a generic “Linux” tag.

    Cheers,
    Matt

    (0) 

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