SQL/MP Reference Manual

HP NonStop SQL/MP Reference Manual—523352-013
X-16
=_SQL_EXE_ESPS_CK_CMON DEFINE
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For information about how to manage double buffering, see the SQL/MP
Installation and Management Guide.
=_SQL_EXE_ESPS_CK_CMON DEFINE
=_SQL_EXE_ESPS_CK_CMON is a system DEFINE that directs SQL to communicate
with the $CMON process whenever it must create a new ESP.
name
must be a legal Guardian file name but has no purpose except to make the ADD
DEFINE command syntactically correct.
Consideration—=_SQL_EXE_ESPS_CK_CMON
In previous RVUs, SQL would send a message to the $CMON process before creating
an ESP. $CMON would reply with a recommendation for a processor in which to create
the new ESP and a priority for running the ESP. However, SQL would ignore the
recommendations returned by the $CMON process. Instead, SQL would create the
new ESP in the processor and at the priority determined by the optimizer (and stored in
the query execution plan).
With the D43 version of SQL/MP software, SQL does not send a message to the
$CMON process before creating a new ESP. For parallel queries involving many
ESPs, this strategy improves the performance of process creation and reduces
query start-up time.
The =_SQL_EXE_ESPS_CK_CMON DEFINE allows you to direct SQL to notify
the $CMON process whenever SQL creates a new ESP. However, even when SQL
notifies the $CMON process before creating an ESP, it does nothing with the
information returned by $CMON.
Example—=_SQL_EXE_ESPS_CK_CMON
This example directs SQL to send a message to the $CMON process before creating
each ESP:
30> ADD DEFINE =_SQL_EXE_ESPS_CK_CMON, CLASS MAP, FILE NOFILE
ADD DEFINE =_SQL_EXE_ESPS_CK_CMON, CLASS MAP, FILE name