SQL/MP Reference Manual

HP NonStop SQL/MP Reference Manual—523352-013

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Consideration—=_SQL_CMP_DOUBLE_SBB_OFF

=_SQL_CMP_DOUBLE_SBB_OFF disables file system double buffering for queries

that are SQL compiled while this DEFINE is in effect.

For information about how to manage double buffering, see the SQL/MP Installation

and Management Guide.

=_SQL_CMP_DOUBLE_SBB_ON DEFINE

=_SQL_CMP_DOUBLE_SBB_ON is a system DEFINE that directs SQL to use file

system double buffering to scan the inner table in a nested join or key-sequenced

merge join.

filename

must be a legal Guardian file name but has no purpose except to make the ADD

DEFINE command syntactically correct.

Considerations—=_SQL_CMP_DOUBLE_SBB_ON



By default, the SQL optimizer considers using file system double buffering for

scans that use VSBB and BROWSE ACCESS except for an inner scan of a nested

join or key-sequenced merge join. When the =_SQL_CMP_DOUBLE_SBB_ON

DEFINE is present, the optimizer also considers using double buffering for these

two types of join operations.



If both =_SQL_CMP_DOUBLE_SBB_ON and =_SQL_CMP_DOUBLE_SBB_OFF

are present, file-system double buffering is not used.

² Double buffering can increase performance, but can also increase the likelihood of

PFS memory overflow. For information about how to manage double buffering, see

the SQL/MP Installation and Management Guide.

ADD DEFINE =_SQL_CMP_DOUBLE_SBB_ON, CLASS MAP,

FILE filename