Understanding innodb_buffer_pool_size

[Marcus]

Which data is stored within the pool size, only the data once fetched from mysql (as "xf_post: rows 2,5,233,2353"), or does mysql store the whole "xf_post" table within database? The following statements are from http://dba.stackexchange.com/questions/27328/how-large-should-be-mysql-innodb-buffer-pool-size

SELECT CEILING(Total_InnoDB_Bytes*1.6/POWER(1024,3)) RIBPS FROM(SELECT SUM(data_length+index_length) Total_InnoDB_Bytes
FROM information_schema.tables WHERE engine='InnoDB') A;

However this shows me that less than 1 GB are used from the cache

SELECT(PagesData*PageSize)/POWER(1024,3) DataGB FROM(SELECT variable_value PagesData
FROM information_schema.global_statusWHERE variable_name='Innodb_buffer_pool_pages_data') A,(SELECT variable_value PageSizeFROM information_schema.global_statusWHERE variable_name='Innodb_page_size') B;

 

[Xon]

InnoDB stores data in blocks in the InnoDB buffer pool, this data can be indexes or actual table data. This is evicted on a Last Recently Used basis (ref)

Indexes actually contain column data + the primary key (ref), this means a query which only hit the indexed columns can get the primary key 'for free' without needing to take a trip to the row record.