Bug #86598 Log a warning when configured innodb_buffer_pool_size is automatically increased
Submitted: 6 Jun 2017 5:03 Modified: 8 Jun 2017 1:03
Reporter: David Bergeron Email Updates:
Status: Open Impact on me:
None 
Category:MySQL Server Severity:S4 (Feature request)
Version:5.7.17 OS:Any
Assigned to: CPU Architecture:Any

[6 Jun 2017 5:03] David Bergeron 
Description:
MySQL should ideally log a severity "Warning" message when configured innodb_buffer_pool_size is impossible to meet and automatically increased because of the innodb_buffer_pool_instances * innodb_buffer_pool_chunk_size requirement.

This would be ideal behaviour for any misconfiguration and will likely save a few people's time in troubleshooting mismatch.

How to repeat:
While leaving innodb_buffer_pool_instances and innodb_buffer_pool_chunk_size to their 8 and 128 MiB defaults, respectively, set innodb_buffer_pool_size to 2.5 GiB in a configuration directive:

innodb_buffer_pool_size  = 2684354560

MySQL will automatically bump it to 3 GiB as if configured to 3 GiB.

Suggested fix:
If the innodb_buffer_pool_size configuration cannot be met and is automatically increased, log a simple message, maybe something like:

[Warning] innodb_buffer_pool_size must be a multiple of the product of innodb_buffer_pool_instances * innodb_buffer_pool_chunk_size.