SQL/MX 2.x Reference Manual (H06.04+)

MXCI Commands
HP NonStop SQL/MX Reference Manual—540440-003
4-17
Examples of DISPLAY_EXPLAIN
This output shows the sequence numbers, the operators, parallel information, and
the cardinality for the operators. Using the sequence numbers, you can create a
query tree that visually shows the query plan.
For more information about parallelism and examples of how to build, display, and
interpret query trees, see the SQL/MX Query Guide.
The DESCRIPTION column contains information about parallelism for an operator.
It has the form:
top degree parallelism (top partitioning function) :
bottom degree parallelism (bottom partitioning function)
where partitioning function can take the following forms:
The output contains an additional column, not shown here, called OPT. OPT
contains additional information for some operators indicating special query
optimizations that were applied. The contents of this column can include:
(hash) hash partitioned n ways on (column ... )
(logph) logphys partitioned (grouping ... )
(range) range partitioned n ways on (column ... )
(rep-b) replicate via broadcast n times
(rep-n) replicate no broadcast n times
( ? ) description missing from plan analysis
Column
Explain
Token: Value Operator Description
o olt_optimization:
used
ROOT,
PA,
SCAN
An indicator that shows whether optimization
for short, simple operations is used. This
applies to online transaction processing.
fs fast_scan: used SCAN An indicator that shows whether an
optimization for simple scan operations is
used.
fr fast_reply: used SCAN An indicator that shows whether an
optimization for returning data from DAM is
used.
r upd_action_on_
error: return
ROOT Query stops executing and error returned
without need for statement rollback.
x upd_action_on_
error:
on_rollback
ROOT Transaction is rolled back if an error occurs.
DEFAULT: UPD_ABORT_ON_ERROR
s upd_action_on_
error: savepoint
ROOT DAM savepoints are used to rollback the
statement if an error occurs.
DEFAULT: UPD_SAVEPOINT_ON_ERROR