InnoDB creates a number of threads to take care of I/O operations, such as read-ahead.
InnoDB.
InnoDB
notices that the access pattern to a segment in the
tablespace is sequential, it posts in advance a batch of
reads of database pages to the I/O system.
InnoDB notices
that some area in a tablespace seems to be in the process of
being fully read into the buffer pool, it posts the
remaining reads to the I/O system.
InnoDB uses a file flush technique called doublewrite.
InnoDB first writes them to a contiguous
tablespace area called the doublewrite buffer.
InnoDB write the pages to their proper
positions in the data file.
InnoDB can later
find a good copy of the page from the doublewrite buffer during
recovery.
How do I defragment a table?
© 2007 John Michael Pierobon