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Oracle® Database PL/SQL Packages and Types Reference
11g Release 2 (11.2)

Part Number E16760-04
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100 DBMS_PARALLEL_EXECUTE

The DBMS_PARALLEL_EXECUTE package enables the user to incrementally update table data in parallel.

See Also:

This chapter contains the following topics:


Using DBMS_PARALLEL_EXECUTE


Overview

This package enables the user to incrementally update table data in parallel, in two high level steps:

  1. Group sets of rows in the table into smaller sized chunks.

  2. Run a user specified statement on these chunks in parallel, and commit when finished processing each chunk.

This package introduces the notion of parallel execution task. This task groups the various steps associated with the parallel execution of a PL/SQL block, which is typically updating table data.

All of the package subroutines (except the GENERATE_TASK_NAME Function and the TASK_STATUS Procedure) perform a commit.


Security Model

DBMS_PARALLEL_EXECUTE is a SYS-owned package which is granted to PUBLIC.

Any user can create or operate his own parallel execution tasks and access the USER view.

Users who have the ADM_PARALLEL_EXECUTE_TASK role can perform administrative routines (qualified by the prefix ADM_) and access the DBA view.

Apart from the administrative routines, all the subprograms refer to tasks owned by the current user.

To execute chunks in parallel, the user must have CREATE JOB system privilege.

The CHUNK_BY_SQL, RUN_TASK, and RESUME_TASK subprograms require a query, and are executed using DBMS_SQL. Invokers of the DBMS_SQL interface must ensure that none of the queries passed-in contains SQL injection.


Constants

The DBMS_PARALLEL_EXECUTE package uses the constants shown in following tables:

Table 100-1 DBMS_PARALLEL_EXECUTE Constants - Chunk Status Value

Constant Type Value Description

ASSIGNED

NUMBER

1

Chunk has been assigned for processing

PROCESSED

NUMBER

2

Chunk has been processed successfully

PROCESSED_WITH_ERROR

NUMBER

3

Chunk has been processed, but an error occurred during processing

UNASSIGNED

NUMBER

0

Chunk is unassigned


Table 100-2 DBMS_PARALLEL_EXECUTE Constants - Task Status Value

Constant Type Value Description

CHUNKED

NUMBER

4

Table associated with the task has been chunked, but none of the chunk has been assigned for processing

CHUNKING

NUMBER

2

Table associated with the task is being chunked

CHUNKING_FAILED

NUMBER

3

Chunking failed

CRASHED

NUMBER

8

Only applicable if parallel execution is used, this occurs if a job slave crashes or if the database crashes during EXECUTE, leaving a chunk in ASSIGNED or UNASSIGNED state.

CREATED

NUMBER

1

The task has been created by the CREATE_TASK Procedure

FINISHED

NUMBER

6

All chunks processed without error

FINISHED_WITH_ERROR

NUMBER

7

All chunks processed, but with errors in some cases

PROCESSING

NUMBER

5

Part of the chunk assigned for processing, or which has been processed



Views

The DBMS_PARALLEL_EXECUTE package uses views listed in the Oracle Database Reference:


Exceptions

The following table lists the exceptions raised by DBMS_PARALLEL_EXECUTE.

Table 100-3 Exceptions Raised by DBMS_PARALLEL_EXECUTE

Exception Error Code Description

CHUNK_NOT_FOUND

29499

Specified chunk does not exist

DUPLICATE_TASK_NAME

29497

Same task name has been used by an existing task

INVALID_STATE_FOR_CHUNK

29492

Attempts to chunk a table that is not in CREATED or CHUNKING_FAILED state

INVALID_STATE_FOR_REDSUME

29495

Attempts to resume execution, but the task is not in FINISHED_WITH_ERROR or CRASHED state

INVALID_STATE_FOR_RUN

29494

Attempts to execute the task that is not in CHUNKED state

INVALID_STATUS

29493

Attempts to set an invalid value to the chunk status

INVALID_TABLE

29491

Attempts to chunk a table by rowid in cases in which the table is not a physical table, or the table is an IOT

MISSING_ROLE

29490

User does not have the necessary ADM_PARALLEL_EXECUTE role

TASK_NOT_FOUND

29498

Specified task_name does not exist



Examples

The following examples run on the Human Resources (HR) schema of the Oracle Database Sample Schemas. It requires that the HR schema be created with the JOB SYSTEM privilege.

Chunk by ROWID

This example shows the most common usage of this package. After calling the RUN_TASK Procedure, it checks for errors and re-runs in the case of error.

DECLARE
  l_sql_stmt VARCHAR2(1000);
  l_try NUMBER;
  l_status NUMBER;
BEGIN
 
  -- Create the TASK
  DBMS_PARALLEL_EXECUTE.CREATE_TASK ('mytask');
 
  -- Chunk the table by ROWID
  DBMS_PARALLEL_EXECUTE.CREATE_CHUNKS_BY_ROWID('mytask', 'HR', 'EMPLOYEES', true, 100);
 
  -- Execute the DML in parallel
  l_sql_stmt := 'update /*+ ROWID (dda) */ EMPLOYEES e 
      SET e.salary = e.salary + 10
      WHERE rowid BETWEEN :start_id AND :end_id';
  DBMS_PARALLEL_EXECUTE.RUN_TASK('mytask', l_sql_stmt, DBMS_SQL.NATIVE,
                                 parallel_level => 10);
 
  -- If there is an error, RESUME it for at most 2 times.
  L_try := 0;
  L_status := DBMS_PARALLEL_EXECUTE.TASK_STATUS('mytask');
  WHILE(l_try < 2 and L_status != DBMS_PARALLEL_EXECUTE.FINISHED) 
  LOOP
    L_try := l_try + 1;
    DBMS_PARALLEL_EXECUTE.RESUME_TASK('mytask');
    L_status := DBMS_PARALLEL_EXECUTE.TASK_STATUS('mytask');
  END LOOP;
 
  -- Done with processing; drop the task
  DBMS_PARALLEL_EXECUTE.DROP_TASK('mytask');
   
END;
/

Chunk by User-Provided SQL

A user can specify their own chunk algorithm by using the CREATE_CHUNKS_BY_SQL Procedure. This example shows that rows with the same manager_id are grouped together and processed in one chunk.

DECLARE
  l_chunk_sql VARCHAR2(1000);
  l_sql_stmt VARCHAR2(1000);
  l_try NUMBER;
  l_status NUMBER;
BEGIN
 
  -- Create the TASK
  DBMS_PARALLEL_EXECUTE.CREATE_TASK ('mytask');
 
  -- Chunk the table by MANAGER_ID
  l_chunk_sql := 'SELECT distinct manager_id, manager_id FROM employees';
  DBMS_PARALLEL_EXECUTE.CREATE_CHUNKS_BY_SQL('mytask', l_chunk_sql, false);
 
  -- Execute the DML in parallel
  --   the WHERE clause contain a condition on manager_id, which is the chunk
  --   column. In this case, grouping rows is by manager_id.
  l_sql_stmt := 'update /*+ ROWID (dda) */ EMPLOYEES e 
      SET e.salary = e.salary + 10
      WHERE manager_id between :start_id and :end_id';
  DBMS_PARALLEL_EXECUTE.RUN_TASK('mytask', l_sql_stmt, DBMS_SQL.NATIVE,
                                  parallel_level => 10);
 
  -- If there is error, RESUME it for at most 2 times.
  L_try := 0;
  L_status := DBMS_PARALLEL_EXECUTE.TASK_STATUS('mytask');
  WHILE(l_try < 2 and L_status != DBMS_PARALLEL_EXECUTE.FINISHED) 
  Loop
    L_try := l_try + 1;
    DBMS_PARALLEL_EXECUTE.RESUME_TASK('mytask');
    L_status := DBMS_PARALLEL_EXECUTE.TASK_STATUS('mytask');
  END LOOP;
 
  -- Done with processing; drop the task
  DBMS_PARALLEL_EXECUTE.DROP_TASK('mytask');
 
end;
/

Executing Chunks in an User-defined Framework

The user can execute chunks in his own defined framework without using the RUN_TASK Procedure. This example shows how to use GET_ROWID_CHUNK Procedure, EXECUTE IMMEDIATE, SET_CHUNK_STATUS Procedure to execute the chunks.

DECLARE
  l_sql_stmt varchar2(1000);
  l_try number;
  l_status number;
  l_chunk_id number;
  l_start_rowid rowid;
  l_end_rowid rowid;
  l_any_rows boolean;
  CURSOR c1 IS SELECT chunk_id
               FROM user_parallel_execute_chunks
               WHERE task_name = 'mytask'
                 AND STATUS IN (DBMS_PARALLEL_EXECUTE.PROCESSED_WITH_ERROR,
                                DBMS_PARALLEL_EXECUTE.ASSIGNED);
BEGIN
 
  -- Create the Objects, task, and chunk by ROWID
  DBMS_PARALLEL_EXECUTE.CREATE_TASK ('mytask');
  DBMS_PARALLEL_EXECUTE.CREATE_CHUNKS_BY_ROWID('mytask', 'HR', 'EMPLOYEES', true, 100);
 
  l_sql_stmt := 'update /*+ ROWID (dda) */ EMPLOYEES e 
      SET e.salary = e.salary + 10
      WHERE rowid BETWEEN :start_id AND :end_id';
 
  -- Execute the DML in his own framework 
  --
  -- Process each chunk and commit.
  -- After processing one chunk, repeat this process until
  -- all the chunks are processed.
  --
  <<main_processing>>
  LOOP
      --
      -- Get a chunk to process; if there is nothing to process, then exit the 
      -- loop;
      --
      DBMS_PARALLEL_EXECUTE.GET_ROWID_CHUNK('mytask',
                                                          l_chunk_id,
                                                          l_start_rowid,
                                                          l_end_rowid,
                                                          l_any_rows);
      IF (l_any_rows = false) THEN EXIT; END IF;
 
      --
      -- The chunk is specified by start_id and end_id.
      -- Bind the start_id and end_id and then execute it
      --
      -- If no error occured, set the chunk status to PROCESSED.
      --
      -- Catch any exception. If an exception occured, store the error num/msg
      -- into the chunk table and then continue to process the next chunk.
      -- 
      BEGIN
        EXECUTE IMMEDIATE l_sql_stmt using l_start_rowid, l_end_rowid;
        DBMS_PARALLEL_EXECUTE.SET_CHUNK_STATUS('mytask',l_chunk_id,
          DBMS_PARALLEL_EXECUTE.PROCESSED);
      EXCEPTION WHEN OTHERS THEN
        DBMS_PARALLEL_EXECUTE.SET_CHUNK_STATUS('mytask', l_chunk_id,
          DBMS_PARALLEL_EXECUTE.PROCESSED_WITH_ERROR, SQLCODE, SQLERRM);
      END;
 
      --
      -- Finished processing one chunk; Commit here
      --
      COMMIT;
  END LOOP;

Summary of DBMS_PARALLEL_EXECUTE Subprograms

Table 100-4 DBMS_PARALLEL_EXECUTE Package Subprograms

Subprogram Description

ADM_DROP_CHUNKS Procedure

Drops all chunks of the specified task owned by the specified owner

ADM_DROP_TASK Procedure

Drops the task of the given user and all related chunks

ADM_TASK_STATUS Procedure

Returns the task status

ADM_STOP_TASK Procedure

Stops the task of the given owner and related job slaves

CREATE_TASK Procedure

Creates a task for the current user

CREATE_CHUNKS_BY_NUMBER_COL Procedure

Chunks the table associated with the given task by the specified column.

CREATE_CHUNKS_BY_ROWID Procedure

Chunks the table associated with the given task by ROWID

CREATE_CHUNKS_BY_SQL Procedure

Chunks the table associated with the given task by means of a user-provided SELECT statement

DROP_TASK Procedure

Drops the task and all related chunks

DROP_CHUNKS Procedure

Drops the task's chunks

GENERATE_TASK_NAME Function

Returns a unique name for a task

GET_NUMBER_COL_CHUNK Procedure

Picks an unassigned NUMBER chunk and changes it to ASSIGNED

GET_ROWID_CHUNK Procedure

Picks an unassigned ROWID chunk and changes it to ASSIGNED

PURGE_PROCESSED_CHUNKS Procedure

Deletes all the processed chunks whose status is PROCESSED or PROCESSED_WITH_ERROR

RESUME_TASK Procedures

Retries the given the task if the RUN_TASK Procedure finished with error, or resumes the task if a crash has occurred.

RUN_TASK Procedure

Executes the specified SQL statement on the chunks in parallel

SET_CHUNK_STATUS Procedure

Sets the status of the chunk

STOP_TASK Procedure

Stops the task and related job slaves

TASK_STATUS Procedure

Returns the task status



ADM_DROP_CHUNKS Procedure

This procedure drops all chunks of the specified task owned by the specified owner.

Syntax

DBMS_PARALLEL_EXECUTE.ADM_DROP_CHUNKS (
   task_owner      IN  VARCHAR2,
   task_name       IN  VARCHAR2);

Parameters

Table 100-5 ADM_DROP_CHUNKS Procedure Parameters

Parameter Description

task_owner

Owner of the task

task_name

Name of the task



ADM_DROP_TASK Procedure

This procedure drops the task of the specified user and all related chunks.

Syntax

DBMS_PARALLEL_EXECUTE.ADM_DROP_TASK (
   task_owner      IN  VARCHAR2,
   task_name       IN  VARCHAR2);

Parameters

Table 100-6 ADM_DROP_TASK Procedure Parameters

Parameter Description

task_owner

Owner of the task

task_name

Name of the task



ADM_TASK_STATUS Procedure

This function returns the task status.

Syntax

DBMS_PARALLEL_EXECUTE.ADM_TASK_STATUS  (
   task_owner      IN  VARCHAR2,
   task_name       IN  VARCHAR2)
 RETURN NUMBER;

Parameters

Table 100-7 ADM_TASK_STATUS Function Parameters

Parameter Description

task_owner

Owner of the task

task_name

Name of the task



ADM_STOP_TASK Procedure

This procedure stops the task of the specified owner and related job slaves.

Syntax

DBMS_PARALLEL_EXECUTE.ADM_STOP_TASK (
   task_owner      IN  VARCHAR2,
   task_name       IN  VARCHAR2);

Parameters

Table 100-8 ADM_STOP_TASK Procedure Parameters

Parameter Description

task_owner

Owner of the task

task_name

Name of the task



CREATE_TASK Procedure

This procedure creates a task for the current user. The pairing of task_name and current_user must be unique.

Syntax

DBMS_PARALLEL_EXECUTE.CREATE_TASK (
   task_name        IN   VARCHAR2,
   comment          IN   VARCHAR2 DEFAULT NULL);

Parameters

Table 100-9 CREATE_TASK Procedure Parameters

Parameter Description

task_name

Name of the task. The task_name can be any string in which related length must be less than or equal to 128 bytes.

comment

Comment field. The comment must be less than 4000 bytes.



CREATE_CHUNKS_BY_NUMBER_COL Procedure

This procedure chunks the table (associated with the specified task) by the specified column. The specified column must be a NUMBER column. This procedure takes the MIN and MAX value of the column, and then divide the range evenly according to chunk_size. The chunks are:

START_ID                              END_ID
---------------------------           ---------------------------
min_id_val                            min_id_val+1*chunk_size-1
min_id_val+1*chunk_size               min_id_val+2*chunk_size-1
…                                     …
min_id_val+i*chunk_size               max_id_val

Syntax

DBMS_PARALLEL_EXECUTE.CREATE_CHUNKS_BY_NUMBER_COL (
   task_name       IN  VARCHAR2,
   table_owner     IN  VARCHAR2,
   table_name      IN  VARCHAR2,
   table_column    IN  VARCHAR2,
   chunk_size      IN  NUMBER);

Parameters

Table 100-10 CREATE_CHUNKS_BY_NUMBER_COL Procedure Parameters

Parameter Description

task_name

Name of the task

table_owner

Owner of the table

table_name

Name of the table

table_column

Name of the NUMBER column

chunk_size

Range of each chunk



CREATE_CHUNKS_BY_ROWID Procedure

This procedure chunks the table (associated with the specified task) by ROWID. num_row and num_block are approximate guidance for the size of each chunk. The table to be chunked must be a physical table with physical ROWID having views and table functions. Index Organized Tables are not allowed.

Syntax

DBMS_PARALLEL_EXECUTE.CREATE_CHUNKS_BY_ROWID (
   task_name       IN  VARCHAR2,
   table_owner     IN  VARCHAR2,
   table_name      IN  VARCHAR2,
   by_row          IN  BOOLEAN,
   chunk_size      IN  NUMBER);

Parameters

Table 100-11 CREATE_CHUNKS_BY_ROWID Procedure Parameters

Parameter Description

task_name

Name of the task

table_owner

Owner of the table

table_name

Name of the table

by_row

TRUE if chunk_size refers to the number of rows, otherwise, chunk_size refers to the number of blocks

chunk_size

Approximate number of rows/blocks to process for each commit cycle



CREATE_CHUNKS_BY_SQL Procedure

This procedure chunks the table (associated with the specified task) by means of a user-provided SELECT statement. The select statement which returns the range of each chunk must have two columns: start_id and end_id. If task is to chunk by ROWID, then the two columns must be of ROWID type. If the task is to chunk the table by NUMBER column, then the two columns must be of NUMBER type. The procedure provides the flexibility to users who want to deploy user-defined chunk algorithms.

Syntax

DBMS_PARALLEL_EXECUTE.CREATE_CHUNKS_BY_SQL (
   task_name       IN  VARCHAR2,
   sql_statement   IN  CLOB,
   by_rowid        IN  BOOLEAN);

Parameters

Table 100-12 CREATE_CHUNKS_BY_SQL Procedure Parameters

Parameter Description

task_name

Name of the task

sql_statment

SQL which returns the chunk ranges

by_rowid

TRUE if the table is chunked by rowids



DROP_TASK Procedure

This procedure drops the task and all related chunks.

Syntax

DBMS_PARALLEL_EXECUTE.DROP_TASK (
   task_name       IN VARCHAR2);

Parameters

Table 100-13 DROP_TASK Procedure Parameters

Parameter Description

task_name

Name of the task



DROP_CHUNKS Procedure

This procedure drops the task's chunks.

Syntax

DBMS_PARALLEL_EXECUTE.DROP_CHUNKS (
   task_name       IN VARCHAR2);

Parameters

Table 100-14 DROP_CHUNKS Procedure Parameters

Parameter Description

task_name

Name of the task



GENERATE_TASK_NAME Function

This function returns a unique name for a task. The name is of the form prefixN where N is a number from a sequence. If no prefix is specified, the generated name is, by default, be TASK$_1, TASK$_2, TASK$_3, and so on. If 'SCOTT' is specified as the prefix, the name is SCOTT1, SCOTT2, and so on.

Syntax

DBMS_PARALLEL_EXECUTE.GENERATE_TASK_NAME (
   prefix      IN      VARCHAR2 DEFAULT 'TASK$_') 
 RETURN VARCHAR2;

Parameters

Table 100-15 GENERATE_TASK_NAME Function Parameters

Parameter Description

prefix

The prefix to use when generating the task name



GET_NUMBER_COL_CHUNK Procedure

This procedure picks an unassigned NUMBER chunk and changes it to ASSIGNED. If there are no more chunks to assign, any_rows is set to FALSE. Otherwise, the chunk_id, start and end_id of the chunk is returned as OUT parameters. The chunk info in DBMS_PARALLEL_EXECUTE_CHUNKS$ is updated as follows: STATUS becomes ASSIGNED; START_TIMESTAMP records the current time; END_TIMESTAMP is cleared.

See Also:

Views

Syntax

DBMS_PARALLEL_EXECUTE.GET_NUMBER_COL_CHUNK (
   task_name       IN VARCHAR2,
   chunk_id        OUT NUMBER,
   start_rowid     OUT ROWID,      
   end_id          OUT ROWID,
   any_rows        OUT BOOLEAN);

Parameters

Table 100-16 GET_NUMBER_COL_CHUNK Procedure Parameters

Parameter Description

task_name

Name of the task

chunk_id

Chunk_id of the chunk

start_rowid

Start rowid in the returned range

end_id

End rowid in the returned range

any_rows

Indicating if there could be any rows to process in the range


Usage Notes

If the task is chunked by ROWID, then get_rowid_range should be used. If the task is chunked by NUMBER column, then get_number_col_range should be used. If the user makes the wrong function call, the returning chunk_id and any_rows has a valid value but start/end_(row)id is NULL.


GET_ROWID_CHUNK Procedure

This procedure picks an unassigned ROWID chunk and changes it to ASSIGNED. If there are no more chunks to assign, any_rows is set to FALSE. Otherwise, the chunk_id, start and end_id of the chunk is returned as OUT parameters. The chunk info in DBMS_PARALLEL_EXECUTE_CHUNKS$ is updated as follows: STATUS becomes ASSIGNED; START_TIMESTAMP records the current time; END_TIMESTAMP is cleared.

See Also:

Views

Syntax

DBMS_PARALLEL_EXECUTE.GET_ROWID_CHUNK (
   task_name       IN VARCHAR2,
   chunk_id        OUT NUMBER,
   start_rowid     OUT ROWID,      
   end_id          OUT ROWID,
   any_rows        OUT BOOLEAN);

Parameters

Table 100-17 GET_ROWID_CHUNK Procedure Parameters

Parameter Description

task_name

Name of the task

chunk_id

Chunk_id of the chunk

start_rowid

Start rowid in the returned range

end_id

End rowid in the returned range

any_rows

Indicating if there could be any rows to process in the range


Usage Notes

If the task is chunked by ROWID, then get_rowid_range should be used. If the task is chunked by NUMBER column, then get_number_col_range should be used. If the user makes the wrong function call, the returning chunk_id and any_rows still have valid value but start/end_(row)id is NULL.


PURGE_PROCESSED_CHUNKS Procedure

This procedure deletes all the processed chunks whose status is PROCESSED or PROCESSED_WITH_ERROR.

Syntax

DBMS_PARALLEL_EXECUTE.PURGE_PROCESSED_CHUNKS (
   task_name       IN VARCHAR2);

Parameters

Table 100-18 PURGE_PROCESSED_CHUNKS Procedure Parameters

Parameter Description

task_name

Name of the task



RESUME_TASK Procedures

This procedure retries the specified the task if the RUN_TASK Procedure finished with error, or resumes the task if a crash has occurred. The user can only invoke this procedure if the task is in a CRASHED or FINISHED_WITH_ERROR state. For a crashed serial execution, the state remains in processing. The FORCE option allows user to resume any task in PROCESSING state. However, it is the user's responsibility to determine that a crash has occurred.The procedure resumes processing the chunks which have not been processed. Also, chunks which are in PROCESSED_WITH_ERROR or ASSIGNED (due to crash) state are processed because those chunks did not commit.This procedure takes the same argument as the RUN_TASK Procedure.The overload which takes task_name as the only input argument re-uses the arguments provided in the previous invoking of the RUN_TASK Procedure or RESUME_TASK Procedures.

Syntax

DBMS_PARALLEL_EXECUTE.RESUME_TASK (
   task_name                     IN  VARCHAR2,
   sql_stmt                      IN  CLOB,   language_flag                 IN  NUMBER,   edition                       IN  VARCHAR2  DEFAULT NULL,   apply_crossedition_trigger    IN  VARCHAR2  DEFAULT NULL,   fire_apply_trigger            IN  BOOLEAN   DEFAULT TRUE,   parallel_level                IN  NUMBER    DEFAULT 0,   job_class                     IN  VARCHAR2  DEFAULT 'DEFAULT_JOB_CLASS',
   force                         IN  BOOLEAN   DEFAULT FALSE);

DBMS_PARALLEL_EXECUTE.RESUME_TASK (
   task_name                     IN  VARCHAR2,
   force                         IN  BOOLEAN   DEFAULT FALSE);

Parameters

Table 100-19 RESUME_TASK Procedure Parameters

Parameter Description

task_name

Name of the task

sql_stmt

SQL statement; must have :start_id and :end_id placeholder

language_flag

Determines how Oracle handles the SQL statement. The following options are recognized:

  • V6 (or 0) specifies version 6 behavior

  • NATIVE (or 1) specifies normal behavior for the database to which the program is connected

  • V7 (or 2) specifies Oracle database version 7 behavior

edition

Specifies the edition to run the statement in. Default is the current edition.

apply_crossedition_trigger

Specifies the unqualified name of a forward crossedition trigger that is to be applied to the specified SQL. The name is resolved using the edition and current_schema setting in which the statement is to be executed. The trigger must be owned by the user who executes the statement.

fire_apply_trigger

Indicates whether the specified apply_crossedition_trigger is itself to be executed, or should only be a guide used in selecting other triggers

parallel_level

Number of parallel jobs; zero if run in serial; NULL uses the default parallelism

job_class

If running in parallel, the jobs all belong to the specified job class

force

If TRUE, do not raise an error if the status is PROCESSING.


Examples

Suppose the chunk table contains the following chunk ranges:

START_ID                              END_ID
---------------------------           ---------------------------
1                                     10
11                                    20
21                                    30

And the specified SQL statement is:

UPDATE employees
      SET salary = salary + 10
      WHERE e.employee_id  BETWEEN :start_id AND :end_id

This procedure executes the following statements in parallel:

UPDATE employees  
      SET salary =.salary + 10  WHERE employee_id BETWEEN 1 and 10; 
      COMMIT;

UPDATE employees  
      SET salary =.salary + 10  WHERE employee_id between 11 and 20;
      COMMIT;

UPDATE employees  
      SET salary =.salary + 10  WHERE employee_id between 21 and 30;
      COMMIT;

RUN_TASK Procedure

This procedure executes the specified statement (sql_stmt) on the chunks in parallel. It commits after processing each chunk. The specified statement must have two placeholders called start_id, and end_id respectively, which represent the range of the chunk to be processed. The types of the placeholder must be rowid where ROWID based chunking was used, or NUMBER where number based chunking was used. The specified statement should not commit unless it is idempotent.

The SQL statement is executed as the current user.

If apply_crossedition_trigger is specified, DBMS_CROSSEDITION_TRIGGER.IS_APPLYING returns true for the sessions executing the SQL. Therefore, for parallel execution, DBMS_CROSSEDITION_TRIGGER.IS_APPLYING returns true in the Job slaves session.

Chunks can be executed in parallel by DBMS_SCHEDULER Job slaves. Therefore, parallel execution requires CREATE JOB system privilege. The Job slaves is created under the current user. The default number of Job slaves is computed as the product of Oracle parameters cpu_count and parallel_threads_per_cpu. On a Real Application Clusters installation, the number of Job slaves is the sum of individual settings on each node in the cluster. This procedure returns only when all the chunks are processed. In parallel cases, this procedure returns only when all the Job slaves finished.

Syntax

DBMS_PARALLEL_EXECUTE.RUN_TASK (
   task_name                     IN  VARCHAR2,
   sql_stmt                      IN  CLOB,   language_flag                 IN  NUMBER,   edition                       IN  VARCHAR2  DEFAULT NULL,   apply_crossedition_trigger    IN  VARCHAR2  DEFAULT NULL,   fire_apply_trigger            IN  BOOLEAN   DEFAULT TRUE,   parallel_level                IN  NUMBER    DEFAULT 0,   job_class                     IN  VARCHAR2  DEFAULT 'DEFAULT_JOB_CLASS');

Parameters

Table 100-20 RUN_TASK Procedure Parameters

Parameter Description

task_name

Name of the task

sql_stmt

SQL statement; must have :start_id and :end_id placeholder

language_flag

Determines how Oracle handles the SQL statement. The following options are recognized:

  • V6 (or 0) specifies version 6 behavior

  • NATIVE (or 1) specifies normal behavior for the database to which the program is connected

  • V7 (or 2) specifies Oracle database version 7 behavior

edition

Specifies the edition to run the statement in. Default is the current edition.

apply_crossedition_trigger

Specifies the unqualified name of a forward crossedition trigger that is to be applied to the specified SQL. The name is resolved using the edition and current_schema setting in which the statement is to be executed. The trigger must be owned by the user executes the statement.

fire_apply_trigger

Indicates whether the specified apply_crossedition_trigger is itself to be executed, or should only be a guide used in selecting other triggers.

parallel_level

Number of parallel jobs; zero if run in serial; NULL uses the default parallelism.\

job_class

If running in parallel, the jobs belong to the specified job class


Examples

Suppose the chunk table contains the following chunk ranges:

START_ID                              END_ID
---------------------------           ---------------------------
1                                     10
11                                    20
21                                    30

And the specified SQL statement is:

UPDATE employees
      SET salary = salary + 10
      WHERE e.employee_id  BETWEEN :start_id AND :end_id

This procedure executes the following statements in parallel:

UPDATE employees  
      SET salary =.salary + 10  WHERE employee_id BETWEEN 1 and 10; 
      COMMIT;

UPDATE employees  
      SET salary =.salary + 10  WHERE employee_id between 11 and 20;
      COMMIT;

UPDATE employees  
      SET salary =.salary + 10  WHERE employee_id between 21 and 30;
      COMMIT;

SET_CHUNK_STATUS Procedure

This procedure sets the status of the chunk. The START_TIMESTAMP and END_TIMESTAMP of the chunk is updated according to the new status:

Value of the new Status               Side Effect
---------------------------           ---------------------------
UNASSIGNED                            START_TIMESTAMP and END_TIMESTAMP 
                                      will be cleared
ASSIGNED                              START_TIMESTAMP will be the current time 
                                      and END_TIMESTAMP will be cleared.
PROCESSED or PROCESSED_WITH_ERROR     The current time will be recorded 
                                      in END_TIMESTAMP

See Also:

Views

Syntax

DBMS_PARALLEL_EXECUTE.SET_CHUNK_STATUS (
   task_name       IN VARCHAR2,
   chunk_id        OUT NUMBER,
   status          IN  NUMBER,
   err_num         IN  NUMBER   DEFAULT NULL,
   err_msg         IN  VARCHAR2 DEFAULT NULL);

Parameters

Table 100-21 SET_CHUNK_STATUS Procedure Parameters

Parameter Description

task_name

Name of the task

chunk_id

Chunk_id of the chunk

status

Status of the chunk: UNASSIGNED, ASSIGNED, PROCESSED PROCESSED_WITH_ERROR

err_num

Error code returned during the processing of the chunk

err_msg

Error message returned during the processing of the chunk



STOP_TASK Procedure

This procedure stops the task and related job slaves.

Syntax

DBMS_PARALLEL_EXECUTE.STOP_TASK (
   task_name       IN VARCHAR2);

Parameters

Table 100-22 STOP_TASK Procedure Parameters

Parameter Description

task_name

Name of the task



TASK_STATUS Procedure

This function returns the task status.

Syntax

DBMS_PARALLEL_EXECUTE.TASK_STATUS (
   task_name       IN VARCHAR2);

Parameters

Table 100-23 TASK_STATUS Procedure Parameters

Parameter Description

task_name

Name of the task