SQL/MX 2.x Query Guide (G06.24+, H06.03+)

Parallelism
HP NonStop SQL/MX Query Guide—523728-003
8-17
Plan Fragments
that communicate with the master executor, this value is always one. The
bottom_degree_parallelism token indicates how many instances exist of the fragment
rooted in this node. The bottom_partitioning_function token provides information about
how the plan is parallelized.
For the SPLIT_TOP operator, the top_degree_parallelism token indicates how many
fragment instances of the fragment containing the SPLIT_TOP node exist. The
bottom_degree_parallelism token indicates how many partitions exist. The
bottom_partitioning_function token provides both logical and physical information about
the parallel plan. The physical information is the most relevant information and shows
you how the fragment is partitioned.
Recognizing the Plan Fragments in a Query Plan
The next series of figures (Figure 8-3 through Figure 8-8) introduces the output that is
obtained with DISPLAY_EXPLAIN OPTIONS 'f' SQLQUERY command and the
query tree with plan fragments identified for this query:
PREPARE SQLQUERY FROM
SELECT l_orderkey, CAST(SUM(l_extendedprice*(1-l_discount))
AS NUMERIC(18,2)), o_orderdate, o_shippriority
FROM customer,orders,lineitem
WHERE c_mktsegment = 'BUILDING'
AND c_custkey = o_custkey
AND l_orderkey = o_orderkey
AND o_orderdate < DATE '1995-03-15'
AND l_shipdate > DATE '1995-03-15'
GROUP BY l_orderkey, o_orderdate, o_shippriority
ORDER BY 2 DESC,3 ASC;
Note. This query is extracted from the TPCD decision support benchmark and the
DISPLAY_EXPLAIN output is obtained by using the DISPLAY_EXPLAIN command with the
OPTIONS 'f' clause. The output portion shown does not include the OPT column. For more
information on the OPTIONS 'f' clause, see the DISPLAY_EXPLAIN command in the SQL/MX
Reference Manual.