DELETE operations are done to a table, often
the values of indexed columns (particularly the values of
secondary keys) are not in sorted order, requiring substantial I/O
to bring secondary indexes up to date. InnoDB has an insert
buffer that caches changes to secondary index entries when the
relevant page is not in the buffer pool, thus avoiding I/O
operations by not reading in the page from the disk. The buffered
changes are merged when the page is loaded to the buffer pool, and
the updated page is later flushed to disk using the normal
mechanism. The InnoDB main thread merges buffered changes when
the server is nearly idle, and during a slow shutdown.
Because it can result in fewer disk reads and writes, this feature is most valuable for workloads that are I/O-bound, for example applications with a high volume of DML operations such as bulk inserts.
However, the insert buffer occupies a part of the buffer pool, reducing the memory available to cache data pages. If the working set almost fits in the buffer pool, or if your tables have relatively few secondary indexes, it may be useful to disable insert buffering. If the working set entirely fits in the buffer pool, insert buffering does not impose any extra overhead, because it only applies to pages that are not in the buffer pool.
Beginning with InnoDB storage engine 1.0.3, you can control whether
InnoDB performs insert buffering with the system configuration
innodb_change_buffering. Beginning with
InnoDB storage engine 1.1, the buffering support is expanded to include
delete operations (when index records are initially marked for
deletion) and purge operations (when index records are physically
deleted). InnoDB storage engine 1.1 also changes the default value from
The allowed values of
The default value: buffer inserts, delete-marking operations, and purges.
Do not buffer any operations.
Buffer insert operations.
Buffer delete-marking operations.
Buffer both inserts and delete-marking.
Buffer the physical deletion operations that happen in the background.
You can set the value of this parameter in the MySQL option file
my.ini) or change
it dynamically with the
SET GLOBAL command,
which requires the
SUPER privilege. Changing
the setting affects the buffering of new operations; the merging
of already buffered entries is not affected.
This is the User’s Guide for InnoDB storage engine 1.1 for MySQL 5.5, generated on 2010-04-13 (revision: 19994) .