15,7GB of 16GB are allocated – only 573MB are free.Shared = Shared memory (details see shared memory section) The most popular way to see the complete memory consumption is the command: free -mĮxample: total used free shared buffers cached Testsystem is a 16GB SLES12 SP4 Application Server with 20 workprocesses. We will start from top to bottom to get some insights. But how can you determine the real usage of a process and may be the complete system? Have you ever added up these values? In the most cases you will bust the physical memory size. With ps -ef or ps axu you can get a static view about the current processes.īut there are a lot of memory information like VSZ/VSS (virtual set size), RSS/RES (resident set size), SHR/SHM (shared memory). The most famous tools are top (default), htop and nmon (contained in the most repositories). The OS memory monitoring is totally useless if you want to use it for monitoring HANA systems. As you may know there is a big difference in cause of the Unix memory concept and how an application handles its memory. The most common Linux systems are mixed mode systems using paging and swapping.Ī lot of customers are asking me in context of monitoring if the systems behavior is correct when the used memory is close to the physical memory size. With paging, when the kernel requires more main memory for an active process, only the least recently used pages of processes are moved to the swap space. To swap a process means to move that entire process out of main memory and to the swap area on hard disk, whereby all pages of that process are moved at the same time. Swapping is the older method of moving data from memory to disk. But is swapping and paging the same?Ī lot of people mean paging when they are talking about swapping. One of the worst things which could happen to such a system in context of performance is swapping or paging. Nowadays the Linux memory management of a SAP system (application server) or SAP HANA system getting more important since the clear roadmap of SAP (Linux as only OS for HANA) is showing that the amount of Linux installations is rising steeply.
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