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

Parallelism
HP NonStop SQL/MX Query Guide—523728-003
8-4
Exchange Nodes and Plan Fragments
For more information about these types of partitioning functions, see the
discussion regarding Join With Matching Partitions on page 8-6.
A plan fragment executes in one of these processes:
•
DAM. A plan fragment executes within the DAM process if and only if its root node
is a PARTITION_ACCESS node.
•
ESP. A plan fragment executes within an ESP process if and only if its root node is
an ESP_EXCHANGE node.
•
Master executor or root. A plan fragment executes in the master executor process
if and only if it contains the ROOT operator.
Multiple instances of a plan fragment can execute in parallel, often on different
processors. Each instance differs from the other instances of the same plan fragment
only in minor details; for example, the partition boundaries. Each instance usually
processes only a part (or partition) of the data.
The next figure shows three plan fragments, DAM (index_scan to partition_access),
ESP (split_top to esp_exchange), and the master executor (sort to root). At run time,
the plan executes as a collection of processes consisting of 12 DAMs (executing the
12 instances of the DAM plan fragment), 4 ESPs (executing the 4 instances of the ESP
fragment), and one master executor process (executing the single instance of the
master executor plan fragment).