MDEV-25342: autosize innodb_buffer_pool_chunk_size
The previous default innodb_buffer_pool_chunk_size of 128M made sense when the innodb buffer pool size was a few GB. When the pool size is 128GB this means the chunk size is 0.1% of this. Fine tuning the buffer pool size on such a fine increment doesn't make practical sense. Also on extremely large buffer pool systems, initializing on the default 128M can also take a considerable amount of time. When large pages are enabled, the chunk size has to be a multiple of an available large page size or memory allocation without use can occur. Previously the default 0 was documented as disabling resizing. With srv_buf_pool_chunk_unit > 0 assertions in the code and the minimium value set, I doubt this was ever the case. As such the autosizing (based on default 0) takes place as follows: * a 64th of the innodb_buffer_pool_size * if large pages, this is rounded down the the nearest multiple of the large page size. * If less than 1MB, set to 1MB. This does mean the new default innodb_buffer_pool_chunk size is 2MB, derived form the above formular with 128MB as the buffer pool size. The innodb_buffer_pool_chunk_size is changed to a size_t for better compatiblity with the memory allocations which use size_t. The previous upper limit is changed to the maxium of a size_t. The maximium value used is the buffer pool size anyway. Getting this default value of the chunk size to a more practical size facilitates further development of more automated resizing without significant overhead or memory fragmentation. innodb_buffer_pool_resize test adjusted based on 1M default chunk size thanks Wlad.
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