IBM 000-8697 OnLine Features High Performance

9-4 IBM Informix OnLine Database Server Administrator’s Guide
OnLine Features
High Performance
OnLine achieves high performance through two mechanisms:
■Raw disk management
■Shared-memory management
OnLine performs its own disk management using raw devices. By storing
tableson one or more raw devices instead of in a standard UNIX file system,
OnLinecan manage the physical organization of data and minimize disk I/O.
Doing so results in three advantages for the user:
■OnLineis not restricted by operating-system limits on the number of
tables that can be accessed concurrently.
■OnLine optimizes table access by storing rows contiguously.
■OnLineeliminates 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 regularUNIX files to store data. In this case,
OnLine manages the file contents but theUNIX operating system manages
theI/O. For more details about OnLine use of raw disk or cooked files, refer
topage 1-40.
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
locatedin 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
page 2-36.