Oracle 5.0, Reference Manual

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Server System Variables
489
read_only
[488] exists only as a
GLOBAL
variable, so changes to its value require the
SUPER
[578] privilege. Changes to
read_only
[488] on a master server are not replicated to
slave servers. The value can be set on a slave server independent of the setting on the master.
Important
In MySQL 5.0, enabling
read_only
does not prevent the use of the
SET
PASSWORD
statement. This is not necessarily the case for all MySQL release
series. When replicating from one MySQL release series to another (for
example, from a MySQL 5.0 master to a MySQL 5.1 slave), you should check
the documentation for the versions running on both master and slave to
determine whether the behavior of
read_only
in this regard is or is not the
same, and, if it is different, whether this has an impact on your applications.
•
read_rnd_buffer_size
[489]
Command-Line Format
--read_rnd_buffer_size=#
Option-File Format
read_rnd_buffer_size
Option Sets Variable Yes,
read_rnd_buffer_size
[489]
Variable Name
read_rnd_buffer_size
Variable Scope Global, Session
Dynamic Variable Yes
Permitted Values
Type
numeric
Default
262144
Range
8200 .. 4294967295
When reading rows in sorted order following a key-sorting operation, the rows are read through this
buffer to avoid disk seeks. See
Section 8.3.1.11, “
ORDER BY
Optimization” . Setting the variable to a
large value can improve
ORDER BY
performance by a lot. However, this is a buffer allocated for each
client, so you should not set the global variable to a large value. Instead, change the session variable
only from within those clients that need to run large queries.
The maximum permissible setting for
read_rnd_buffer_size
[489] is 2GB.
read_buffer_size
[488] and
read_rnd_buffer_size
[489] are not specific to any storage
engine and apply in a general manner for optimization. See Section 8.9.4, “How MySQL Uses
Memory” , for example.
•
relay_log_purge
[489]
Command-Line Format
--relay_log_purge
Option-File Format
relay_log_purge
Option Sets Variable Yes,
relay_log_purge
[489]
Variable Name
relay_log_purge
Variable Scope Global
Dynamic Variable Yes
Permitted Values
Type
boolean
Default
TRUE