Resizing the buffer pool is performed in chunks determined by the size of the innodb_buffer_pool_chunk_size variable.

The resize operation waits until all active transactions and operations are completed, and new transactions and operations that need to access the buffer pool must wait until the resize is complete (although when decreasing the size, access is permitted when defragmenting and withdrawing pages).

Nested transactions may fail if started after the buffer pool resize has begun.

The new buffer pool size must be a multiple of innodb_buffer_pool_chunk_size * innodb_buffer_pool_instances. If you attempt to set a different figure, the value is automatically adjusted to a multiple of at least the attempted size. Note that adjusting the innodb_buffer_pool_chunk_size setting can result in a change in the buffer pool size.

The number of chunks as calculated by innodb_buffer_pool_size / innodb_buffer_pool_chunk_size should not exceed 1000 in order to avoid performance issues.

A background thread performs the resizing operation. The Innodb_buffer_pool_resize_status status variable shows the progress of the resizing operation, for example:

SHOW STATUS LIKE 'Innodb_buffer_pool_resize_status';
+----------------------------------+----------------------------------+
| Variable_name                    | Value                            |
+----------------------------------+----------------------------------+
| Innodb_buffer_pool_resize_status | Resizing also other hash tables. |
+----------------------------------+----------------------------------+

or

SHOW STATUS LIKE 'Innodb_buffer_pool_resize_status';
+----------------------------------+----------------------------------------------------+
| Variable_name                    | Value                                              |
+----------------------------------+----------------------------------------------------+
| Innodb_buffer_pool_resize_status | Completed resizing buffer pool at 161103 16:26:54. |
+----------------------------------+----------------------------------------------------+

Progress is also logged in the error log.