SQL/MP Version Management Guide

Version Compatibility for SQL Programs

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

7-17

Execution Performance in Mixed Version Networks

Reverting to an older version of SQL/MP software on a node in a network can cause

performance degradation when the execution plan calls for parallel execution. Migrating

to a newer version of the software might result in the use of less than optimal query

execution plans.

Performance and Older Version Software

The performance of an SQL program that uses parallel execution to access objects on a

remote node can be less than optimal if the remote node reverts to an older version of

SQL/MP software. In such a case, these situations can occur:

•

If software on the node reverts to an older version after SQL compilation of a

program, the executor server process on the reverted node might not be available.

(Version 1 SQL software does not support executor server processes, and an

executor server process on a node using version 2 software might not be able to

support queries that use new features.) If the remote node does not support executor

server processes, a warning is issued, and the executor starts an executor server

process on the local node. Because the executor server process on the local node

must now read remote data, performance is degraded.

•

If the execution plan calls for a disk process on a remote node to evaluate a

predicate compiled for a newer version of the software, the system returns a version

error and execution stops.

In each of these cases, the solution is to recompile the program with an older version

SQL compiler. The compiler executes a query execution plan based on the type of

Figure 7-5. Effect of Reverting to Older Version Software

Version 315

Object

Node Running

Version 2 NonStop SQL

(Reverted From Version 315)

Node Running

Version 315 NonStop SQL/MP

Version 315

Object

Access attempts result in version errors.

VST019.vsd

Version 315

SQL Program

Version 2

SQL Program