MySQL read hard drive data

The smallest administrative unit of the InnoDB is the page

InnoDB Minimum Application unit is the district, a district 1M, contains 64 pages, each page 16K, that is, 64*16k=1m, taking into account the hard disk locality, each read 4 extents, that is, read 4M of data loaded into memory

Linear Pre-reading:

After the read thread of InnoDB reads 4M data from disk, if the data of the pages connected to the 4 extents is greater than or equal to Innodb_read_ahead_threshold (the default is 56), the data in the next 4 extents is then load to memory

Attention:

InnoDB Storage Engine This book says at least apply 4 data to the drive,

But most articles say that only 1 districts of data are requested, first of all

Reference

Http://www.oschina.net/translate/making-full-table-scan-10x-faster-in-innodb

MySQL read hard drive data