Download Informix Guide to SQL: Tutorial, Version 6.0

INFORMIX-OnLine Dynamic Server Disk Storage
Tables and Spaces
A table resides completely in one dbspace. (Its blob values can reside in
separate blobspaces or on an optical storage subsystem.) If no dbspace is
specified, a table resides in the dbspace where its database resides. The
following partial example creates a table in the dbspace named misctabs:
CREATE TABLE taxrates (…column specifications…) IN misctabs
You can achieve many aims by placing a table in a specific dbspace. Some of
these aims are explored in the following paragraphs.
Exploiting Mirroring
Place all the tables used by a critically important application in a mirrored
dbspace. Alternatively, create the database in the mirrored dbspace and let
the important tables reside there by default. Tables that are part of the database, but that are not used by the critical programs, can be located in
nonmirrored spaces.
Sharing Temporary Space
When databases are large and disk space is limited, the normal dbspaces
might not have enough room for those large temporary tables that can be
helpful in improving query performance. However, a temporary table exists
only for the life of the program that creates it—even less time if the program
drops the table promptly. Set up a single dbspace for temporary tables, so it
can be used repeatedly by many programs.
Assigning Dedicated Hardware
A dbspace can equal a chunk, and a chunk can equal a device. Thus, you can
place a table on a disk device that is dedicated to its use. When disk drives
have different performance levels, you can put the tables with the highest
frequency of use on the fastest drives.
By giving a high-use table a dedicated access arm, you can reduce contention
with applications that use other tables. This does not reduce contention
between programs using the same table unless the table itself is spread across
multiple devices, as suggested in the next section.
10-6 Tuning Your Data Model