This appendix documents Oracle Parallel Server compatibility issues and restrictions.
The following sections describe aspects of compatibility between shared and exclusive modes on a parallel server.
The Export and
The Export utility writes data from an Oracle database into operating system files, and the Import utility reads data from those files back into an Oracle database. This feature of Oracle is the same in shared or exclusive mode.
See Also: Oracle7 Server Utilities for more information about Import and Export.
Compatibility Between Shared and Exclusive Modes
A parallel server runs with any Oracle database created in exclusive mode. Each instance must have its own set of redo logs.
Oracle in exclusive mode can access a database created or modified by
a parallel server.
If a parallel server allocates free space to a specific instance, that space is not be available for inserts for a different instance in exclusive mode. Of course, all data in the allocated extents is always available.
The following sections describe restrictions.
Fine Grain Locking
Support for fine grain locking is platform-dependent. Additionally, fine grain locking is disabled by default. Check with Oracle World Wide Support to find the current status of this feature on your platform.
Support for this feature is platform-dependent.
Maximum Number of Blocks Allocated at a Time
The !blocks option of the GC_FILES_TO_LOCKS parameter enables you to control the number of blocks which are available for use within a free list group. You can use !blocks to specify the rate at which blocks are allocated within an extent, up to 255 blocks at a time.
Restrictions in Shared Mode
Oracle running multiple instances in shared mode supports all the functionality of Oracle in exclusive mode, except as noted in the following sections.
Restricted SQL Statements
In shared mode, the following operations are not supported:
- creating a database (CREATE DATABASE)
- creating a control file (CREATE CONTROLFILE)
To perform these operations, you must shut down all instances and start up one instance in exclusive mode, as described in "Starting Up Instances" .
- switching the database's archiving mode (the ARCHIVELOG and NOARCHIVELOG options of ALTER DATABASE)
Maximum Number of Datafiles
The number of datafiles supported by Oracle is operating system specific. Within this limit, the maximum number allowed depends on the values used in the CREATE DATABASE command, which in turn is limited by the physical size of the control file. This limit is the same in shared mode as in exclusive mode, but the additional instances of a parallel server restrict the maximum number of files more than a single-instance system. For more details, see the Oracle7 Server SQL Reference manual, and your Oracle operating system specific documentation.
Sequence Number Generators
Oracle Parallel Server does not support the CACHE ORDER combination of options for sequence number generators in shared mode. Sequences created with both of these options are ordered but not cached when running in a parallel server.
For GC_RELEASABLE LOCKS you must specify a value equal to or greater than the value of DB_BLOCK_BUFFERS.
Free Lists with Import and Export Utilities
The Export utility does not preserve information about multiple free lists and free list groups. When you export data from multiple instances and then, from a single node, import it into a file, the data may not end up distributed across extents in exactly the same way it was initially. The meta-data of the table into which it is imported contains the free list and free list group information which is henceforth associated with the datablocks.
Therefore, if you use Export and Import to back up and restore your data, it will be difficult to import the data so that it is partitioned again.