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Oracle Parallel Processing by Sanjay Mishra, Tushar Mahapatra

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PCM Lock Allocation Parameters and Verification

There are three initialization parameters that control the allocation of PCM locks in an OPS environment:

GC_FILES_TO_LOCKS

Controls PCM lock allocation to datafiles. The value of this parameter must be the same for all instances of an OPS database.

GC_RELEASABLE_LOCKS

Allocates releasable locks. The value of this parameter may be different for each instance of an OPS database.

GC_ROLLBACK_LOCKS

Specifies the number of locks available for each rollback segment that is being modified concurrently. The value of this parameter must be the same for all instances of an OPS database.

The following sections describe these parameters, how you can use them to best advantage, and how you can verify lock allocation.

The GC_FILES_TO_LOCKS Parameter

This parameter specifies the manner in which PCM locks are allocated to different datafiles. It specifies the number of locks allocated to a specific file, and/or to a set of datafiles, except for those files that contain rollback segments. The GC_ROLLBACK_LOCKS parameter is used to allocate locks to files with rollback segments.

GC_FILES_TO_LOCKS syntax

The syntax for the GC_FILES_TO_LOCKS parameter is rather complex and looks like this:

GC_FILES_TO_LOCKS = "LOCK_ALLOCATION[:LOCK_ALLOCATION...]"

LOCK_ALLOCATION := FILE_LIST=num_locks[!blocking][R][EACH]

FILE_LIST := fileid[-fileid][,fileid[-fileid]...]
LOCK_ALLOCATION

Allocates a specific number of locks to one or more files. Multiple LOCK_ALLOCATION entries are ...

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