Memory Usage always high despite increased capacity

[shenoybipin]

My question is about how Linux manages the memory. I went through the articles & other posts in the forums but did not find an answer. Hence posting this. We have a DB server that caters to requests from development environment. We recently increased the Memory from 4GB to 32GB but still there is no significant increase in Memory Percentage Used.


Before Upgrade

Total RAM 4 GB
Average Percentage Used: 95-100%
Swap Used?: Mostly yes
1 Oracle Instance
1 Mysql Instance

After Upgrade

Total RAM 32 GB
Average Percentage Used: 90-100%
Swap USed?: Rarely used
2 Oracle Instances
1 Mysql Instance

Total SGA limit (similar to max_memory to be used at run time) is 4GB for both instances of oracle togther. We are concerned what would happen when the load on the DB increases, especially once the UAT environment is active.

Snapshot from of /proc/meminfo:

MemTotal:     32184436 kB
MemFree:       1897560 kB
Buffers:        795596 kB
Cached:       24977916 kB
SwapCached:         92 kB
Active:        9190560 kB
Inactive:     19979156 kB

The Inactive Memory is almost always around 20GB. Is that normal? and will Linux automatically take care of it when the load increases?

[Rubberman]

This is normal, especially for database servers. In the original instance, when you had only 4GB of ram, the swap space was being used extensively, which had a major negative impact upon performance. With 32GB of RAM, most (~25GB) is being used for system cache, to speed up data access. If you need that memory for program code/data, then the OS will release it using an LRU (Least Recently Used) algorithm, rather than going to swap. I'd say it was healthy for a machine running two Oracle database instances.

[shenoybipin]

This is normal, especially for database servers. In the original instance, when you had only 4GB of ram, the swap space was being used extensively, which had a major negative impact upon performance. With 32GB of RAM, most (~25GB) is being used for system cache, to speed up data access. If you need that memory for program code/data, then the OS will release it using an LRU (Least Recently Used) algorithm, rather than going to swap. I'd say it was healthy for a machine running two Oracle database instances.

Thanks for the quick reply, Rubberman. This is relieving.