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

Parallelism
HP NonStop SQL/MX Query Guide—523728-003
8-21
Degree of Parallelism
Degree of Parallelism
Each plan fragment has its own degree of parallelism, as indicated by the tokens for
the exchange operators in the operator description field of the EXPLAIN output. Note
that the query plan shown in Figure 8-6 has one root fragment, two ESP fragments,
and three DAM fragments. For this query plan, the relevant information for the degree
of parallelism is contained in the descriptions of each ESP_EXCHANGE operator. The
PARTITION_ACCESS nodes provide information about the beginning and ending key
predicates, which instruct each DAM fragment where to start and stop for the partitions
it handles.
Figure 8-6. Sample Query Plan Showing Plan Fragments
VST089.vsd
root [13]
hybrid_hash_join [9]
esp exchange [8]
merge_join [7]
esp exchange [12]
sort [11]
hash_groupby [10]
partition access [4] partition access [6]
file_scan [3] - CUSTOMER
index_scan [5] - ORDERX1
1
2(range)
2(range)
top_degree_parallelism
bottom_degree_parallelism
Root Fragment
(Master Executor)
ESP Plan Fragments
top_degree_parallelism
bottom_degree_parallelism
DAM Plan Fragments
2(range)
partition access [2]
file_scan [1] - LINEITEM