I know the consensus seems to be approximately 75% of ram should be dedicated to the buffer pool. But, I'm more interested in the optimal number of buffer pool instances. What are some things to consider when determining the setting?

For example, let's say I have a 75GB buffer pool. Should I just assign 75 buffer pool instances at 1GB each? 15 at 5GB each? Or, 10 at 7.5GB each?

Should I start out with a single buffer pool and increase based on whether or not I see locking?

What should the max number of instances be based on - available cores?

Thanks - Your response is greatly appreciated.

  • This is an excellent question. I have not seen much talk about a rule-of-thumb around the buffer pool on the web lately. +1 !!! Apr 3, 2014 at 15:20

2 Answers 2



The rule of thumb I usually use is based on a special program in in the Linux environment

numactl --hardware

When I run this, I get the following output

sh-4.1# numactl --hardware
available: 4 nodes (0-3)
node 0 cpus: 0 1 2 3
node 0 size: 49151 MB
node 0 free: 241 MB
node 1 cpus: 4 5 6 7
node 1 size: 32768 MB
node 1 free: 39 MB
node 2 cpus: 8 9 10 11
node 2 size: 49152 MB
node 2 free: 49 MB
node 3 cpus: 12 13 14 15
node 3 size: 32752 MB
node 3 free: 32 MB
node distances:
node   0   1   2   3
  0:  10  16  16  16
  1:  16  10  16  16
  2:  16  16  10  16
  3:  16  16  16  10

This quickly tells me how many CPUs and cores I have on my DB Server.

In general, I set the innodb_buffer_pool_instances to the number of physical CPUs or the number of cores. In your particular, I set the innodb_buffer_pool_instances to 4 or 16.


If you make the InnoDB Buffer Pool bigger than 50% of the installed RAM, mysqld causes the OS to start swapping ... BADLY !!!! If you need a Buffer Pool that big, then tuning innodb_buffer_pool_instances becomes even more critical.


As soon as innodb_buffer_pool_instances was first introduced, I immediately experimented with it. I had a client that had 192GB DB Server, dual hexacore with a 162GB Buffer Pool. I simply set it to 2 and everything worked out just fine. Please see my old post from Feb 12, 2011 on this : How do you tune MySQL for a heavy InnoDB workload?


  • Thanks Rolando! - Great explanation as always. Interesting to see your test progression for finding the correct size. Out of curiosity, what were the swap results from your findings? How do you tune MySQL for a heavy InnoDB workload? - You mentioned following up in the last update, but I don't see any further comments. Apr 6, 2014 at 11:10

You should use combination of innodb_buffer_pool_size in accourdance with innodb_buffer_pool_instances

You should set the innodb_buffer_pool_instances configuration option to a value greater than 1 (the default) up to 64 (the maximum). This option takes effect only when you set the innodb_buffer_pool_size to a size of 1 gigabyte or more. The total size you specify is divided among all the buffer pools. For best efficiency, specify a combination of innodb_buffer_pool_instances and innodb_buffer_pool_size so that each buffer pool instance is at least 1 gigabyte.


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