Property Description
Parameter type String


Spaces are not allowed within the quotation marks.

Default value There is no default value.
Modifiable No
Basic No
Real Application Clusters You must set this parameter for every instance, and multiple instances must have identical values. To change the value, you must shut down all instances in the cluster, change the value for each instance, and then start up each instance.


Setting this parameter to any value other than the default will disable Cache Fusion processing in a Real Application Clusters environment.

GC_FILES_TO_LOCKS is a Real Application Clusters parameter that has no effect on an instance running in exclusive mode. It controls the mapping of pre-release 9.0.1 parallel cache management (PCM) locks to datafiles.


  • file_list

    One or more datafiles listed by their file numbers, or ranges of file numbers, with comma separators:


    To find the correspondence between filenames and file numbers, query the FILE_NAME and FILE_ID columns of the DBA_DATA_FILES data dictionary view.

  • lock_count

    The number of PCM locks assigned to file_list. By default these locks are fixed. If you set lock_count to 0, then Oracle uses fine-grain locking for these files and takes locks as needed from the pool of releasable locks.

  • blocks

    Specifies the number of contiguous blocks covered by one lock. The default is noncontiguous blocks.

  • EACH

    Indicates that each datafile in file_list is assigned a separate set of lock_count PCM locks.

The value of the parameter should be set to cover as many files as possible. Therefore, to avoid performance problems, you should always change GC_FILES_TO_LOCKS when the size of datafiles change or when new datafiles are added. Doing so requires you to shut down and restart your cluster database.

If the number of PCM locks allocated to a datafile is less than or equal to the number of blocks in a datafile, each of these locks will cover a number of contiguous blocks within the datafile equal to blocks. If the number of PCM locks assigned to the datafile is larger than its number of blocks, resources will be wasted because some locks will not be covering any blocks.

A colon (:) separates each clause that assigns a number of PCM locks to file_list.

See Also:

Oracle Real Application Clusters Administration and Deployment Guide and the Oracle Database Oracle Clusterware and Oracle Real Application Clusters Installation Guide for your operating system for more information on setting this parameter