MariaDB RAM usage does not reflect configuration

Question

I've got 256GB RAM. InnoDB pool buffer size is 128GB, and InnoDB data + indexes in all databases are about 105GB. Most of that data is frequently queried so, correct me if I am wrong, it should reside in buffer_pool?

I thought that innodb_buffer_pool resides in RAM, but top command shows:

MiB Mem : 257873.0 total,    747.0 free,  74239.4 used, 182886.6 buff/cache

Most of users complain about high RAM usage, and in my case it seems that MariaDB is not using all the RAM it should?

ulimit -v says 'unlimited'.

Is that ok? Can I force putting entire innodb_buffer_pool in RAM, and if so, then how?

Answer 1

MariaDB's memory usage grows over time. It stops growing when certain configurable settings are hit. In practice, it mostly stops growing long before the 'theoretical' limit is hit.

The buffer_pool is allocated only in RAM. It is the main memory user that grows over time, stopping when it hits innodb_buffer_pool_size.

Since the buffer_pool is a "cache", the data can be much bigger than the buffer_pool; the downside is the need to do more I/O to pull "blocks" of data (or indexes) into the cache, bumping out other blocks.

If all of the activity is concentrated on a subset of the data (eg, "recent" items), then the buffer_pool grows until "big enough" and may not actually expand to innodb_buffer_pool_size. I/O activity will be low.

If the buffer_pool is bigger than all the InnoDB data and indexes you have, it will grow to about that size and then simply stay at that size.

The innodb_buffer_pool_size should not be so large that you run out of RAM. When that happens, swapping occurs. If there is no swap space, then the process is killed.