Oracle8 Server Migration
Release 8.0
A54650_01

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General System Requirements for Migration to Oracle8

This appendix discusses the system requirements for successful migration, upgrading, and downgrading operations. Migrating a database from Oracle7 (or Version 6, by using Export/Import) to Oracle8 requires some specific configurations of operating system and hardware. Topics covered in this chapter include:

Memory Requirements

Total Oracle8 memory requirements consist of basic memory requirements, memory needed for executables, and amount of concurrent access.

Basic Memory Requirements

Oracle8 requires at least 48 megabytes of RAM to run a database (minimum configuration without much operating system memory swapping to disk). To support connections to multiple users, the system should provide additional memory. Concurrent use of the Enterprise Manager should be supported with an additional 20MB. See the operating system-specific Oracle documentation for more information on memory requirements specific to the platform.

Oracle8 Executables

The Oracle8 executables are three times larger than Oracle7 executables, primarily because of new functionalities added in Oracle8. Using a typical 3-megabyte set of Oracle7 executables, space required for these executables upon migration to Oracle8 could approximate 9 megabytes. This threefold increase can require special attention on large batch systems (which may generate dozens to hundreds of executables). The space actually required for executables also depends on the options chosen for the Oracle8 environment, such as:

Oracle Parallel Server (see the Oracle8 Parallel Server Concepts & Administration book for details)
Net8 or SQL*Net use (see the Net3 Administrator's Guide )

Be sure to adjust system memory to accommodate the inclusion of such options when migrating from Oracle7 to Oracle8.

Note: The use of shared objects on many platforms provides some reduction in the size of client applications. However, the size of some shared objects (or libraries) can be quite large due to new functionality in the Oracle8 release.

Concurrent Access

The memory size of an Oracle8 system also depends on concurrent access and how that access is accomplished. Oracle8 provides for the following connect options:

Use local connections in dedicated server architecture (also called "two-task Oracle") (same as Oracle7).
Use remote connections through SQL*Net (same as Oracle7).
Use multithreaded shared servers for local and remote connections.
Use transaction processor (TP) monitors.

Option 1 requires more memory than option 2 or option 3. With option 1, if both client application and its Oracle server (or shadow) process reside on the same machine, memory is required for both. For example, 100 client application processes connected to Oracle8 results in 100 additional Oracle server processes on the system, totaling 200 in all.

With option 2, only the Oracle processes reside on the system, and the client processes are connected remotely. Thus, you need to pay attention only to the size of the Oracle server processes and the size of the available shared memory.

Option 3, using multithreaded server architecture, is the same as Oracle7. The multithreaded server feature allows the processes of several local or remote client processes to connect to a single dispatcher process instead of having a dedicated Oracle shadow process. While not meant as a performance enhancement, multithreaded server configuration allows more concurrent connections on an Oracle8 server, thereby improving throughput. Multiple clients can connect to a single dispatcher, so the memory utilization for concurrent user connections decreases. For further information on the multithreaded server feature of Oracle8, refer to Oracle8 Server Concepts.

Option 4, use of TP monitors, is an alternative for systems requiring a high number of users (greater than several hundred) all performing OLQP/OLTP type transactions. Such transactions are usually short-lived and do not require the user to make a direct connection to the database. All transactions are performed with messages routed by the TP (transaction processor) monitor service. The TP layer provides named services and coordinates service requests with various DBMS systems, including Oracle. The requirements for using TP monitors vary greatly and are beyond the scope of this manual. Please consult the appropriate TP monitor vendor for system requirements.

In summary, you should be able to estimate system memory requirements, for a single system, by considering the following factors:

the average number of open cursors and cursors that may cause sorts for a given Oracle application session
the average size of the Oracle shadow processes that will include open cursors and sort areas
the peak number of concurrent users on the system
the average memory size of the Oracle front-end application

Using Oracle Parallel Server

Migration of the Oracle Parallel Server (including DLM) requires that each node have its own copy of Oracle7 and Oracle8 software. Many platforms, including IBM RS6000, NCR 3XXX series, Pyramid MIS Server, Sequent Symmetry, and Sun SPARKCenter may require additional private disks.

Oracle8 New Sizes and Limits

Oracle8 increased various capacity limits, as shown in the following listing:

Datatypes:

CHAR increased to 2000 bytes.
VARCHAR/VARCHAR2 increased to 4000 bytes.
NCHAR holds up to 2000 bytes.
NCHAR VARYING holds up to 4000 bytes.

Columns and indexes:

Database size is limited only by capacity of the platform.
Maximum number of datafiles per tablespace is 1022.
Maximum number of columns in a table increased to 1000.
Primary key is limited to 16 fields.

CHAR and NCHAR Maximum Size Support

Oracle8 supports increased maximum string lengths for several datatypes:

CHAR maximum length of 2000 bytes (also for RAW datatype)
(Oracle 7.3 supports CHAR and RAW length maxima of 255 bytes)
VARCHAR2 maximum length of 4000 bytes
(Oracle 7.3 supports a VARCHAR2 length maximum of 2000 bytes)

The Oracle8 datatype string length maxima accord with the NTT/MIA specification, which requires the following string lengths:

CHAR maximum length of at least 255 bytes
NCHAR maximum length of 127 characters
NCHAR VARYING (NVARCHAR) max length of 2000 characters
VARCHAR2 maximum length of 4000 bytes