IBM 000-8697 User Manual

IBM Informix OnLine Database Server Administrator’s Guide

OnLine achieves high performance through two mechanisms:

■

Raw disk management

■

Shared-memory management

OnLine performs its own disk management using raw devices. By storing
tables on one or more raw devices instead of in a standard

UNIX

file system,

OnLine can manage the physical organization of data and minimize disk

I/O

.

Doing so results in three advantages for the user:

■

OnLine is not restricted by operating-system limits on the number of
tables that can be accessed concurrently.

■

OnLine optimizes table access by storing rows contiguously.

■

OnLine eliminates operating-system overhead by performing direct
data transfer between disk and shared memory.

If exceptional performance or reliability is not a primary concern, you can
also configure OnLine to use regular

UNIX

 files to store data. In this case,

OnLine manages the file contents but the

UNIX

 operating system manages

the

I/O

. For more details about OnLine use of raw disk or cooked files, refer

to

.

All applications that use OnLine share the same memory data space. After
one database server process reads data from a table, other processes can
access whatever data is already in memory. Disk access might not be
required.

OnLine shared memory contains both data from the database and control
information. Because all data that might be needed by all applications is
located in a single, shared portion of memory, all control information needed
to manage access to that data can be located in the same place.

For more information about OnLine shared-memory management refer to