NonStop SQL/MP Reference Manual

NonStop SQL/MP Reference Manual—142115
Z-15
=_SQL_EXE_ESPS_CK_CMON DEFINE
=_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 needs to 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.
Considerations—=_SQL_EXE_ESPS_CK_CMON
•
In previous releases, SQL would send a message to the $CMON process before
creating an ESP. $CMON would reply with a recommendation for a CPU 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 CPU and at the priority determined by the optimizer (and
stored in the query execution plan).
With the D43 version of NonStop 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.
Examples—=_SQL_EXE_ESPS_CK_CMON
•
The following 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
=_SQL_EXE_USE_SWAPVOL DEFINE
=_SQL_EXE_USE_SWAPVOL is a system DEFINE that directs SQL to allocate
temporary tables for serial plans on the swap volume for the process.
name
must be a legal Guardian file name but has no purpose except to make the ADD
DEFINE command syntactically correct.
ADD DEFINE =_SQL_EXE_ESPS_CK_CMON, CLASS MAP, FILE name
ADD DEFINE =_SQL_EXE_USE_SWAPVOL, CLASS MAP, FILE name