SQL/MP Version Management Guide

Version Compatibility for SQL Programs
Compaq NonStop™ SQL/MP Version Management Guide—429833-001
7-16
SQL Execution and Fallback Nodes
version 1. The exceptions to this general rule are the following cases, in which the
executor uses newer version features:
•
Software corrections released with a newer version of SQL/MP software that change
program behavior
•
Features of older version SQL programs that change program behavior
As described under SQL Compilation in a Mixed Version Network
on page 7-7 the
query execution plan might not be the most optimal plan, but it will execute.
An SQL executor can use query execution plans that call for parallel execution when all
the nodes accessed by the SQL program are version 2 or newer. The SQL compiler does
not consider parallel execution if any accessed node is version 1.
Access to objects on remote nodes can be affected if the SQL/MP software on any of the
remote nodes reverts to an older version or migrates to a newer version. Changing the
version of the software does not normally cause program invalidation; however,
program invalidation or version errors can occur in certain situations.
SQL Execution and Fallback Nodes
Reverting to an older version can cause version errors for either an SQL program or for
queried objects on the node with the older version software.
The version of SQL objects accessed by a query can cause execution problems if the
node where the objects reside reverts to an older version of SQL/MP software. No newer
version objects can be created on a node running older version software, but if the
software reverts to an older version after the objects are created, the version of the object
can be newer than the version of the software. Attempts to access such objects result in a
file system error or a version error.
The version of SQL objects on a remote node causes execution problems if the software
on the local node querying the objects reverts to an older version. If the version of the
software on the local node reverts to an older version after compilation, attempts to
access objects on either the remote or local node result in version errors. Attempts to
recompile the program result also in version errors. The only solution is to reinstall a
newer version of the software on the node.
Figure 7-5
illustrates the effect on SQL execution of reverting to an older version of
SQL/MP software on a node in a network.