InnoDB
Startup Options and System Variables
1243
in hardware caches, or use some other command specific to the hardware
vendor.
•
innodb_flush_method
Command-Line Format
--innodb_flush_method=name
Option-File Format
innodb_flush_method
Option Sets Variable
Yes,
innodb_flush_method
[1243]
Variable Name
innodb_flush_method
Variable Scope
Global
Dynamic Variable
No
Permitted Values
Type
(windows)
enumeration
Default
async_unbuffered
If set to
fdatasync
(the default),
InnoDB
uses
fsync()
to flush both the data and log files. If set to
O_DSYNC
,
InnoDB
uses
O_SYNC
to open and flush the log files, and
fsync()
to flush the data files.
If
O_DIRECT
is specified (available on some GNU/Linux versions, FreeBSD, and Solaris),
InnoDB
uses
O_DIRECT
(or
directio()
on Solaris) to open the data files, and uses
fsync()
to flush both
the data and log files. Note that
InnoDB
uses
fsync()
instead of
fdatasync()
, and it does not
use
O_DSYNC
by default because there have been problems with it on many varieties of Unix. This
variable is relevant only for Unix. On Windows, the flush method is always
async_unbuffered
and
cannot be changed.
Different values of this variable can have a marked effect on
InnoDB
performance. For example,
on some systems where
InnoDB
data and log files are located on a SAN, it has been found that
setting
innodb_flush_method
[1243]
to
O_DIRECT
can degrade performance of simple
SELECT
statements by a factor of three.
•
innodb_force_recovery
Command-Line Format
--innodb_force_recovery=#
Option-File Format
innodb_force_recovery
Option Sets Variable
Yes,
innodb_force_recovery
[1243]
Variable Name
innodb_force_recovery
Variable Scope
Global
Dynamic Variable
No
Permitted Values
Type
enumeration
Default
0
Valid
Values
0
1
2
3
4
5
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