Question & Answer
Question
Why does the free command shows constant high memory usage?
-bash-4.2$ free -h
total used free shared buff/cache available
Mem: 47G 46G 490M 0M 226M 17G
-/+ buffers/cache: 29G 18G
Swap: 7.8G 0B 7.8G
The amount of used memory never goes down. Why is memory usage so high? Is there a memory leak?
Cause
The IBM Resilient® appliance contains multiple services, such as:
- IBM Resilient service
- IBM Resilient Messaging service
- IBM Resilient Email service
- PostgreSQL database
- Elasticsearch
Each of these services, along with the operating system, consumes system memory.
Answer
When the appliance boots up, the IBM Resilient® services reserve their predefined minimum memory. They will request more memory as needed, up to their predefined maximum memory limit. After they reach their limits, they will not request more memory.
The IBM Resilient service is configured to use half of the system memory. On a system with 32 GB of RAM, IBM Resilient uses 16 GB. The other services will use several GBs more.
All memory is managed by the operating system. Modern operating systems do not leave memory unused. They set aside a small amount of the available memory to be allocated to applications quickly. The rest of the memory is used to cache files to reduce the amount of disk I/O, which improves the overall system performance. The database benefits from the file cache because it allows faster access to the data. Instead of having to fetch the records from the disk, the records are fetched from the file cache, which is much faster than disk level access. If an application requests more memory than what's available in free memory, the operating system releases the required memory from the cache and allocate it to the application.
With the IBM Resilient® services requesting more memory as the appliance "warms up", and the operating system making use of the free memory, you'll see the amount of free memory decrease over time. This behavior is normal.
If the IBM Resilient appliance is performing poorly, it is not due to memory leaks. Contact IBM Resilient support so we can assist you with troubleshooting any performance problems.
Related Information
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Document Information
Modified date:
19 April 2021
UID
ibm16223282