SQL/MP Version Management Guide

Version Compatibility for SQL Programs

Compaq NonStop™ SQL/MP Version Management Guide—429833-001

7-14

Using Parallel Execution Plans in a Mixed Version

Network

Using Parallel Execution Plans in a Mixed Version Network

Starting with version 2 SQL software, you can request the SQL compiler to process

queries in parallel by setting the CONTROL EXECUTOR PARALLEL directive to ON.

Parallel execution of queries can significantly improve performance when a database

spans multiple disks.

When parallel execution is enabled, the SQL compiler can also select plans that use

executor server processes to perform parallel execution. If a network includes nodes

using version 1 SQL software, such a plan cannot work, because the version 1 software

does not have executor server processes. In such a situation, the SQL compiler does not

select a plan that takes advantage of executor server processing.

A version 300 or newer SQL compiler might also select a parallel execution strategy

that uses hash joins to process queries. If any partitions of a queried table reside on a

node whose SQL software version is older than 300, the hash join optimization cannot

be used, because hash joins can be performed only by version 300 or newer software.

Figure 7-3. Query Execution Plans in a Mixed Version Network

Node Running

Version 315 NonStop SQL

Table A Table B Table C

No Optimization

of Exponentiation,

OR Predicates, or

Unsigned Decimal

Numbers

No Optimization

Using Alternate

Collating Sequence

Node Running

Version 315 NonStop SQL

Node Running

Version 1 NonStop SQL

Node Running

Version 2 NonStop SQL

All Features of

Version 315

Query Execution

Plan

SQL compiler does not use version 315 query execution plan.

1 1

VST017.vsd

SQL

Compiler