Oracle 5.0, Справочное руководство

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Server System Variables
488
Block
Size
1024
The size of blocks that are allocated when doing range optimization.
•
read_buffer_size
[488]
Command-Line Format
--read_buffer_size=#
Option-File Format
read_buffer_size
Option Sets Variable Yes,
read_buffer_size
[488]
Variable Name
read_buffer_size
Variable Scope Global, Session
Dynamic Variable Yes
Permitted Values
Type
numeric
Default
131072
Range
8200 .. 2147479552
Each thread that does a sequential scan allocates a buffer of this size (in bytes) for each table it
scans. If you do many sequential scans, you might want to increase this value, which defaults to
131072. The value of this variable should be a multiple of 4KB. If it is set to a value that is not a
multiple of 4KB, its value will be rounded down to the nearest multiple of 4KB.
The maximum permissible setting for
read_buffer_size
[488] 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.
•
read_only
[488]
Command-Line Format
--read-only
Option-File Format
read_only
Option Sets Variable Yes,
read_only
[488]
Variable Name
read_only
Variable Scope Global
Dynamic Variable Yes
Permitted Values
Type
boolean
Default
false
This variable is off by default. When it is enabled, the server permits no updates except from users
that have the
SUPER
[578] privilege or (on a slave server) from updates performed by slave
threads. In replication setups, it can be useful to enable
read_only
[488] on slave servers to
ensure that slaves accept updates only from the master server and not from clients.
read_only
[488] does not apply to
TEMPORARY
tables as of MySQL 5.0.16. This variable does
not prevent the use of
ANALYZE TABLE
or
OPTIMIZE TABLE
statements because its purpose is
to prevent changes to table structure or contents. Analysis and optimization do not qualify as such
changes. This means, for example, that consistency checks on read-only slaves can be performed
with
mysqlcheck --all-databases --analyze
.