HP Integrity NonStop J-Series - Manual (Page 90)

File Relocation Facility
HP NonStop Storage Management Foundation User's Guide—523562-007
5-4
Query Recompilation
Shorthand views can be relocated from one disk to another without consideration for
where the base tables on which they are identified are located.
Query Recompilation
The file relocation operation does not force automatic query recompilation. However,
under certain circumstances, users might want to recompile queries that refer to the
objects that have been relocated. In particular, if a table or index that is referred to in a
parallel query plan has moved onto a disk whose primary process runs in a different
processor than that of the table or index, users might see slightly better performance
by explicitly recompiling the query. Note that recompilation is not required for the query
to return correct results.
Users can determine which programs refer to a particular table by using the USAGES
table in the catalog where the relocated file is registered.
Relocating SQL Catalog Files
The files that make up the SQL catalog (including the system catalog) can be relocated
independently. For example, BASETABS can be placed on a different disk than
USAGES by using file relocation interfaces.
Caution. Relocating files independently can relieve space shortages on a particular disk and
possibly improve performance, but users should also be aware of the following:
If a catalog’s component files are spread over multiple disks, there is an increased chance that
the catalog can become unavailable due to the increased number of disks that can become
unavailable. Therefore, if catalog files are to be placed on multiple disk volumes, HP
recommends that all such volumes be mirrored.
If fallback to direct volumes is required, the SQL catalog will be corrupted if all catalog
component files are not on the same disk. For more information on fallback and migration
procedures, see
Section 4, Migration Guidelines .