Oracle 5.0, Справочное руководство

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Server System Variables
477
Dynamic Variable Yes
Permitted Values (>= 5.0)
Type
enumeration
Valid
Values
nulls_equal
nulls_unequal
nulls_ignored
How the server treats
NULL
values when collecting statistics about the distribution of index values
for
MyISAM
tables. This variable has three possible values,
nulls_equal
,
nulls_unequal
, and
nulls_ignored
. For
nulls_equal
, all
NULL
index values are considered equal and form a single
value group that has a size equal to the number of
NULL
values. For
nulls_unequal
,
NULL
values
are considered unequal, and each
NULL
forms a distinct value group of size 1. For
nulls_ignored
,
NULL
values are ignored.
The method that is used for generating table statistics influences how the optimizer chooses indexes
for query execution, as described in
Section 8.5.4, “
MyISAM
Index Statistics Collection” .
Any unique prefix of a valid value may be used to set the value of this variable.
This variable was added in MySQL 5.0.14. For older versions, the statistics collection method is
equivalent to
nulls_equal
.
•
named_pipe
[477]
Variable Name
named_pipe
Variable Scope Global
Dynamic Variable No
Platform Specific windows
Permitted Values
Type
(windows)
boolean
Default
OFF
(Windows only.) Indicates whether the server supports connections over named pipes.
•
net_buffer_length
[477]
Command-Line Format
--net_buffer_length=#
Option-File Format
net_buffer_length
Option Sets Variable Yes,
net_buffer_length
[477]
Variable Name
net_buffer_length
Variable Scope Global, Session
Dynamic Variable Yes
Permitted Values
Type
numeric
Default
16384
Range
1024 .. 1048576
Each client thread is associated with a connection buffer and result buffer. Both begin
with a size given by
net_buffer_length
[477] but are dynamically enlarged