SQL/MP Query Guide

Improving Query Performance With Environmental
Options
HP NonStop SQL/MP Query Guide—524488-003
4-15
Requesting Parallel Operations on Partitioned Data
The master executor assigns one ESP process to each partition that must be
accessed. At run time, the master executor starts an ESP process in the current
primary processor of each partition’s disk volume (unless an existing ESP process can
be used).
Each ESP works only on the partition to which it is assigned. The master executor
simultaneously employs a number of ESPs to work in parallel on the chosen part of the
statement. If the table is partitioned across multiple nodes, the ESPs are started on the
nodes where the data resides.
For more information on ESPs, see Processor Assignment by the SQL/MP Optimizer
and Executor for Executor Server Processes (ESPs) on page 2-5.
Figure 4-1 shows how the master executor assigns four ESPs to perform a SELECT
operation on a table with four partitions. Each ESP selects data from one partition and
returns it to the master executor.
Figure 4-1. Parallel Execution of a SELECT Statement
VST0401.vsd
Volume
Containing
Partition 1
Vol ume
Containing
Partition 2
Volume
Containing
Partition 3
Volume
Cont aini ng
Partition 4
Disk Process Disk Process Disk Process Disk Process
ESPES PESPESP
SELECT SELECT SELECT SELECT
Applic ation Proces s
SQL Master
Exec utor
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