SQL/MP Reference Manual

HP NonStop SQL/MP Reference Manual—523352-013
S-32
SERIALWRITES File Attribute
SERIALWRITES File Attribute
SERIALWRITES is a Guardian file attribute that specifies whether to write data serially
or in parallel to the two disk devices that make up a mirrored volume. SERIALWRITES
applies to key-sequenced, relative, and entry-sequenced tables and to indexes.
The table default is NO SERIALWRITES.
The index default is its table's value at index creation.
Considerations—SERIALWRITES

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.

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.
{ SERIALWRITES | NO SERIALWRITES }
SERIALWRITES Selects serial mirror writes
NO SERIALWRITES Selects parallel mirror writes
SET DEFINE { LIKE define } [, attr value ] ... ;
{ attr value }