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.. _buff_read_ahead_area:
====================================
Fixed Size for the Read Ahead Area
====================================
|InnoDB| dynamically calculates the size of the read-ahead area in case it has to trigger its read-ahead algorithm. When the workload involves heavy I/O operations, this size is computed so frequently that it has a non-negligeable impact on the CPU usage.
This variable only depends on the size of the buffer pool set by the :variable:`innodb_buffer_pool_size` variable, and as soon as the buffer pool has a size properly greater than 1024 pages (or 16 MB), it is always 64. With this change, its value is fixed to 64, thus removing a bottleneck experienced by some users.
Please note that the minimum allowed value for the |InnoDB| buffer pool is de facto set to 32 MB.
This change is a port of the feature from Facebook:
* http://bazaar.launchpad.net/~mysqlatfacebook/mysqlatfacebook/5.1/revision/3538
Version Specific Information
============================
* :rn:`5.5.8-20.0` :
Full functionality available.
Other Information
=================
* Author/Origin:
Facebook
* Bugs fixed:
:bug:`606811`
Other Reading
=============
* `BUF_READ_AHEAD_AREA Bottleneck <http://www.facebook.com/notes/mysqlfacebook/using-pmp-to-double-mysql-throughput-part-2/405092575932>`_
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