NonStop SQL/MP Reference Manual

NonStop SQL/MP Reference Manual—142115
S-33
Considerations—SERIALWRITES
The index default is its table's value at index creation.
Considerations—SERIALWRITES
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Selecting a SERIALWRITES value
For audited tables and indexes, use NO SERIALWRITES. For nonaudited tables or
indexes, weigh the value of performance versus data reliability. SERIALWRITES
can degrade response time, but it can also improve the reliability of data not
protected by TMF auditing.
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Explanation of serial versus parallel writes
SERIALWRITES tells the system to write one data block at a time to a mirrored pair
of disks. If a system failure occurs, the failure affects only one disk, so the system
uses the good copy of the data block after the failure.
With parallel writes (NO SERIALWRITERS), the system writes to both disks of a
mirrored pair simultaneously; performance is improved, but a system failure can
affect both copies of the block being written.
SET DEFINE Command
SET DEFINE is an SQLCI command that sets a value for one or more DEFINE
attributes in the working attribute set. The working attribute set determines values for
attributes you do not specify in an ADD DEFINE command. (SET DEFINE is similar to
the TACL command SET DEFINE and the OSS command set_define.)
LIKE define
specifies the name of an existing DEFINE to use as a model for the new values of
the working attribute set, optionally modified by attr value pairs that follow the
LIKE clause.
If you use the LIKE clause, you cannot specify the CLASS attribute.
attr value
is the name and value of a DEFINE attribute to add to the working attribute set. (See
DEFINEs on page D-26 for information about DEFINE attributes.)
Considerations—SET DEFINE
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The working attribute set consists of values for the attributes of the current class.
Only one class of attributes can be in the working set at one time.
SET DEFINE { LIKE define } [, attr value ] ... ;
{ attr value }