69 DBMS_PCLXUTIL

The DBMS_PCLXUTIL package provides intra-partition parallelism for creating partition-wise local indexes. DBMS_PCLXUTIL circumvents the limitation that, for local index creation, the degree of parallelism is restricted to the number of partitions as only one slave process for each partition is used.

Overview

DBMS_PCLXUTIL uses the DBMS_JOB package to provide a greater degree of parallelism for creating a local index for a partitioned table. This is achieved by asynchronous inter-partition parallelism using the background processes (with DBMS_JOB), in combination with intra-partition parallelism using the parallel query slave processes.

DBMS_PCLXUTIL works with both range and range-hash composite partitioning.

The DBMS_PCLXUTIL package can be used during the following DBA tasks:

Local index creation

The procedure BUILD_PART_INDEX assumes that the dictionary information for the local index already exists. This can be done by issuing the create index SQL command with the UNUSABLE option.

CREATE INDEX <idx_name> on <tab_name>(...) local(...) unusable;

This causes the dictionary entries to be created without "building" the index itself, the time consuming part of creating an index. Now, invoking the procedure BUILD_PART_INDEX causes a concurrent build of local indexes with the specified degree of parallelism.

EXECUTE dbms_pclxutil.build_part_index(4,4,<tab_name>,<idx_name>,FALSE);

For composite partitions, the procedure automatically builds local indexes for all subpartitions of the composite table.

Local index maintenance

By marking desired partitions usable or unusable, the BUILD_PART_INDEX procedure also enables selective rebuilding of local indexes. The force_opt parameter provides a way to override this and build local indexes for all partitions.

ALTER INDEX <idx_name> local(...) unusable;

Rebuild only the desired (sub)partitions (that are marked unusable):

EXECUTE dbms_pclxutil.build_part_index(4,4,<tab_name>,<idx_name>,FALSE);

Rebuild all (sub)partitions using force_opt = TRUE:

EXECUTE dbms_pclxutil.build_part_index(4,4,<tab_name>,<idx_name>,TRUE);

A progress report is produced, and the output appears on screen when the program is ended (because the DBMS_OUTPUT package writes messages to a buffer first, and flushes the buffer to the screen only upon termination of the program).

Operational Notes

DBMS_PCLXUTIL submits a job for each partition. It is the responsibility of the user/dba to control the number of concurrent jobs by setting the INIT.ORA parameter JOB_QUEUE_PROCESSES correctly. There is minimal error checking for correct syntax. Any errors are reported in the job queue process trace files.

Rules and Limits

Note:

For range partitioning, the minimum compatibility mode is 8.0; for range-hash composite partitioning, the minimum compatibility mode is 8i.

Because DBMS_PCLXUTIL uses the DBMS_JOB package, you must be aware of the following limitations pertaining to DBMS_JOB:

You must decide appropriate values for the job_queue_processes initialization parameter. Clearly, if the job processes are not started before calling BUILD_PART_INDEX(), then the package will not function properly. The background processes are specified by the following init.ora parameters:

job_queue_processes=n   #the number of background processes = n

Failure conditions are reported only in the trace files (a DBMS_JOB limitation), making it impossible to give interactive feedback to the user. This package prints a failure message, removes unfinished jobs from the queue, and requests the user to take a look at the j*.trc trace files.

Summary of DBMS_PCLXUTIL Subprograms

Table 69-1 DBMS_PCLXUTIL Package Subprograms

Subprogram	Description
BUILD_PART_INDEX Procedure	Provides intra-partition parallelism for creating partition-wise local indexes

BUILD_PART_INDEX Procedure

This procedure provides intra-partition parallelism for creating partition-wise local indexes.

Syntax

DBMS_PCLXUTIL.BUILD_PART_INDEX ( 
   jobs_per_batch  IN NUMBER   DEFAULT 1,
   procs_per_job   IN NUMBER   DEFAULT 1, 
   tab_name        IN VARCHAR2 DEFAULT NULL, 
   idx_name        IN VARCHAR2 DEFAULT NULL, 
   force_opt       IN BOOLEAN  DEFAULT FALSE);

Parameters

Table 69-2 BUILD_PART_INDEX Procedure Parameters

Parameter	Description
`jobs_per_batch`	The number of concurrent partition-wise "local index builds".
`procs_per_job`	The number of parallel query slaves to be utilized for each local index build (1 <= `procs_per_job` <= `max_slaves`).
`tab_name`	The name of the partitioned table (an exception is raised if the table does not exist or not partitioned).
`idx_name`	The name given to the local index (an exception is raised if a local index is not created on the table `tab_name`).
`force_opt`	If `TRUE`, then force rebuild of all partitioned indexes; otherwise, rebuild only the partitions marked '`UNUSABLE`'.

Examples

Suppose a table PROJECT is created with two partitions PROJ001 and PROJ002, along with a local index IDX.

A call to the procedure BUILD_PART_INDEX(2,4,'PROJECT','IDX',TRUE) produces the following output:

SQLPLUS> EXECUTE dbms_pclxutil.build_part_index(2,4,'PROJECT','IDX',TRUE); 
Statement processed. 
INFO: Job #21 created for partition PROJ002 with 4 slaves 
INFO: Job #22 created for partition PROJ001 with 4 slaves