117 DBMS_SESSION

Using DBMS_SESSION

• Security Model

• Operational NotesOperational Notes

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Security Model

This package runs with the privileges of the calling user, rather than the package owner SYS.

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Operational Notes

You should not attempt to turn close_cached_open_cursors on or off.

Summary of DBMS_SESSION Subprograms

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CLEAR_ALL_CONTEXT Procedure

Syntax

DBMS_SESSION.CLEAR_ALL_CONTEXT
   namespace         VARCHAR2);

Parameters

Usage Notes

This procedure must be invoked directly or indirectly by the trusted package.

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CLEAR_CONTEXT Procedure

Syntax

DBMS_SESSION.CLEAR_CONTEXT
   namespace         VARCHAR2,
   client_identifier VARCHAR2
   attribute         VARCHAR2);

Parameters

Usage Notes

This procedure must be invoked directly or indirectly by the trusted package.

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CLEAR_IDENTIFIER Procedure

This procedure removes the set_client_id in the session.

Syntax

DBMS_SESSION.CLEAR_IDENTIFIER;

Usage Notes

This procedure is executable by public.

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CLOSE_DATABASE_LINK Procedure

This procedure closes an open database link. It is equivalent to the following SQL statement:

ALTER SESSION CLOSE DATABASE LINK <name>

Syntax

DBMS_SESSION.CLOSE_DATABASE_LINK (
   dblink VARCHAR2);

Parameters

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FREE_UNUSED_USER_MEMORY Procedure

This procedure reclaims unused memory after performing operations requiring large amounts of memory (more than 100K).

Examples of operations that use large amounts of memory include:

• Large sorting where entire sort_area_size is used and sort_area_size is hundreds of KB.

• Compiling large PL/SQL packages, procedures, or functions.

• Storing hundreds of KB of data within PL/SQL indexed tables.

You can monitor user memory by tracking the statistics "session UGA memory" and "session PGA memory" in the v$sesstat or v$statname fixed views. Monitoring these statistics also shows how much memory this procedure has freed.

Syntax

DBMS_SESSION.FREE_UNUSED_USER_MEMORY;

Return Values

The behavior of this procedure depends upon the configuration of the server operating on behalf of the client:

• Dedicated server: This returns unused PGA memory and session memory to the operating system. Session memory is allocated from the PGA in this configuration.

• Shared server: This returns unused session memory to the shared_pool. Session memory is allocated from the shared_pool in this configuration.

Usage Notes

In order to free memory using this procedure, the memory must not be in use.

After an operation allocates memory, only the same type of operation can reuse the allocated memory. For example, after memory is allocated for sort, even if the sort is complete and the memory is no longer in use, only another sort can reuse the sort-allocated memory. For both sort and compilation, after the operation is complete, the memory is no longer in use, and the user can call this procedure to free the unused memory.

An indexed table implicitly allocates memory to store values assigned to the indexed table's elements. Thus, the more elements in an indexed table, the more memory the RDBMS allocates to the indexed table. As long as there are elements within the indexed table, the memory associated with an indexed table is in use.

The scope of indexed tables determines how long their memory is in use. Indexed tables declared globally are indexed tables declared in packages or package bodies. They allocate memory from session memory. For an indexed table declared globally, the memory remains in use for the lifetime of a user's login (lifetime of a user's session), and is freed after the user disconnects from ORACLE.

Indexed tables declared locally are indexed tables declared within functions, procedures, or anonymous blocks. These indexed tables allocate memory from PGA memory. For an indexed table declared locally, the memory remains in use for as long as the user is still running the procedure, function, or anonymous block in which the indexed table is declared.After the procedure, function, or anonymous block is finished running, the memory is then available for other locally declared indexed tables to use (in other words, the memory is no longer in use).

Assigning an uninitialized, "empty" indexed table to an existing index table is a method to explicitly re-initialize the indexed table and the memory associated with the indexed table. After this operation, the memory associated with the indexed table is no longer in use, making it available to be freed by calling this procedure. This method is particularly useful on indexed tables declared globally which can grow during the lifetime of a user's session, as long as the user no longer needs the contents of the indexed table.

The memory rules associated with an indexed table's scope still apply; this method and this procedure, however, allow users to intervene and to explicitly free the memory associated with an indexed table.

Examples

The following PL/SQL illustrates the method and the use of procedure FREE_UNUSED_USER_MEMORY.

CREATE PACKAGE foobar
   type number_idx_tbl is table of number indexed by binary_integer;

   store1_table  number_idx_tbl;     --  PL/SQL indexed table
   store2_table  number_idx_tbl;     --  PL/SQL indexed table
   store3_table  number_idx_tbl;     --  PL/SQL indexed table
   ...
END;            --  end of foobar

DECLARE
   ...
   empty_table   number_idx_tbl;     --  uninitialized ("empty") version
BEGIN
   FOR i in 1..1000000 loop
     store1_table(i) := i;           --  load data
   END LOOP;
   ...
   store1_table := empty_table;      --  "truncate" the indexed table
   ... 
   -
   dbms_session.free_unused_user_memory;  -- give memory back to system

   store1_table(1) := 100;           --  index tables still declared;
   store2_table(2) := 200;           --  but truncated.
   ...
END;

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IS_ROLE_ENABLED Function

This function determines if the named role is enabled for this session.

Syntax

DBMS_SESSION.IS_ROLE_ENABLED (
   rolename    VARCHAR2) 
  RETURN BOOLEAN;

Parameters

Return Values

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IS_SESSION_ALIVE Function

This function determines if the specified session is active.

Syntax

DBMS_SESSION.IS_SESSION_ALIVE (
   uniqueid VARCHAR2) 
  RETURN BOOLEAN;

Parameters

Return Values

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LIST_CONTEXT Procedures

This procedure returns a list of active namespaces and contexts for the current session.

Syntax

TYPE AppCtxRecTyp IS RECORD ( 
   namespace VARCHAR2(30), 
   attribute VARCHAR2(30),
   value     VARCHAR2(256)); 

TYPE AppCtxTabTyp IS TABLE OF AppCtxRecTyp INDEX BY BINARY_INTEGER; 

DBMS_SESSION.LIST_CONTEXT ( 
   list OUT AppCtxTabTyp, 
   size OUT NUMBER);

Parameters

Return Values

Usage Notes

The context information in the list appears as a series of <namespace> <attribute> <value>. Because list is a table type variable, its size is dynamically adjusted to the size of returned list.

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MODIFY_PACKAGE_STATE Procedure

This procedure can be used to perform various actions (as specified by the action_flags parameter) on the session state of all PL/SQL program units active in the session. This takes effect after the PL/SQL call that made the current invocation finishes running. The procedure uses the DBMS_SESSION constants listed in Table 117-12.

Syntax

DBMS_SESSION.MODIFY_PACKAGE_STATE(
   action_flags IN PLS_INTEGER); 

Parameters

Usage Notes

See the parameter descriptions in Table 117-13 for the differences between the flags and why DBMS_SESSION.REINITIALIZE exhibits better performance than DBMS_SESSION.FREE_ALL_RESOURCES.

• Reinitialization refers to the process of resetting all package variables to their initial values and running the initialization block (if any) in the package bodies. Consider the package:

package P is
      n number;
      m number := P2.foo;
      d date := SYSDATE;
      cursor c is select * from emp;
      procedure bar;
    end P;
    /
    package body P is
      v   varchar2(20) := 'hello';
      procedure bar is
      begin
        ...
      end;
      procedure init_pkg is
      begin
        ....
      end;
    begin
      -- initialization block
      init_pkg;
      ...
      ...
    end P;
    /

For the package P, reinitialization involves:

• Setting P.n to NULL

• Invoking function P2.foo and setting P.m to the value returned from P2.foo

• Setting P.d to the return value of SYSDATE built-in

• Closing cursor P.c if it was previously opened

• Setting P.v to 'hello'

• Running the initialization block in the package body

• The reinitialization for a package is done only if the package is actually referenced subsequently. Furthermore, the packages are reinitialized in the order in which they are referenced subsequently.

• When using FREE_ALL_RESOURCES or REINITIALIZE, make sure that resetting package variable values does not affect the application.

• Because DBMS_SESSION.REINITIALIZE does not actually cause all the package state to be freed, in some situations, the application could use significantly more session memory than if the FREE_ALL_RESOURCES flag or the RESET_PACKAGE procedure had been used. For instance, after performing DBMS_SESSION.MODIFY_PACKAGE_STATE(DBMS_SESSION.REINITIALIZE), if the application does not refer to many of the packages that were previously referenced, then the session memory for those packages will remain until the end of the session (or until DBMS_SESSION.RESET_PACKAGE is called).

• Because the client-side PL/SQL code cannot reference remote package variables or constants, you must explicitly use the values of the constants. For example, DBMS_SESSION.MODIFY_PACKAGE_STATE(DBMS_SESSION.REINITIALIZE)does not compile on the client because it uses the constant DBMS_SESSION.REINITIALIZE.

  Instead, use DBMS_SESSION.MODIFY_PACKAGE_STATE(2) on the client, because the argument is explicitly provided.

Examples

This example illustrates the use of DBMS_SESSION.MODIFY_PACKAGE_STATE. Consider a package P with some global state (a cursor c and a number cnt). When the package is first initialized, the package variable cnt is 0 and the cursor c is CLOSED. Then, in the session, change the value of cnt to 111 and also execute an OPEN operation on the cursor. If you call print_status to display the state of the package, you see that cnt is 111 and that the cursor is OPEN. Next, call DBMS_SESSION.MODIFY_PACKAGE_STATE. If you print the status of the package P again using print_status, you see that cnt is 0 again and the cursor is CLOSED. If the call to DBMS_SESSION.MODIFY_PACKAGE_STATE had not been made, then the second print_status would have printed 111 and OPEN.

create or replace package P is
  cnt    number := 0;
  cursor c is select * from emp;
  procedure print_status;
end P;
/
show errors;

create or replace package body P is
  procedure print_status is
  begin
    dbms_output.put_line('P.cnt = ' || cnt);
    if c%ISOPEN then
      dbms_output.put_line('P.c is OPEN');
    else
      dbms_output.put_line('P.c is CLOSED');
    end if;
  end;
end P;
/
show errors;

SQL> set serveroutput on;
SQL> begin
  2   P.cnt := 111;
  3   open p.c;
  4   P.print_status;
  5  end;
  6  /
P.cnt = 111
P.c is OPEN

PL/SQL procedure successfully completed.

SQL> begin
  2   dbms_session.modify_package_state(dbms_session.reinitialize);
  3  end;
  4  /

PL/SQL procedure successfully completed.

SQL> set serveroutput on;
SQL>
SQL> begin
  2   P.print_status;
  3  end;
  4  /
P.cnt = 0
P.c is CLOSED

PL/SQL procedure successfully completed.

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SESSION _TRACE_DISABLE Procedure

This procedure resets the session-level SQL trace for the session from which it was called. Client ID and service/module/action traces are not affected.

Syntax

DBMS_SESSION.SESSION_TRACE_ENABLE();

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SESSION _TRACE_ENABLE Procedure

This procedure enables session-level SQL trace for the invoking session. Invoking this procedure results in SQL tracing of every SQL statement issued by the session.

Syntax

DBMS_SESSION.SESSION_TRACE_ENABLE(
   waits     IN   BOOLEAN DEFAULT TRUE,��
   binds     IN   BOOLEAN DEFAULT FALSE, 
   �plan_stat IN   VARCHAR2 DEFAULT NULL);

Parameters

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RESET_PACKAGE Procedure

This procedure de-instantiates all packages in this session. It frees the package state.

Memory used for caching the execution state is associated with all PL/SQL functions, procedures, and packages that were run in a session.

For packages, this collection of memory holds the current values of package variables and controls the cache of cursors opened by the respective PL/SQL programs. A call to RESET_PACKAGE frees the memory associated with each of the previously run PL/SQL programs from the session, and, consequently, clears the current values of any package globals and closes any cached cursors.

RESET_PACKAGE can also be used to reliably restart a failed program in a session. If a program containing package variables fails, then it is hard to determine which variables need to be reinitialized. RESET_PACKAGE guarantees that all package variables are reset to their initial values.

Syntax

DBMS_SESSION.RESET_PACKAGE; 

Usage Notes

Because the amount of memory consumed by all executed PL/SQL can become large, you might use RESET_PACKAGE to trim down the session memory footprint at certain points in your database application. However, make sure that resetting package variable values will not affect the application. Also, remember that later execution of programs that have lost their cached memory and cursors will perform slower, because they need to re-create the freed memory and cursors.

RESET_PACKAGE does not free the memory, cursors, and package variables immediately when called.

For example, PL/SQL procedure P1 calls PL/SQL procedure P2, and P2 calls RESET_PACKAGE. The RESET_PACKAGE effects do not occur until procedure P1 finishes execution (the PL/SQL call ends).

Examples

This SQL*Plus script runs a large program with many PL/SQL program units that may or may not use global variables, but it doesn't need them beyond this execution:

EXCECUTE large_plsql_program1; 
 

To free up PL/SQL cached session memory:

EXECUTE DBMS_SESSION.RESET_PACKAGE; 
 

To run another large program:

EXECUTE large_plsql_program2;

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SET_CONTEXT Procedure

This procedure sets the context, of which there are four types: session local, globally initialized, externally initialized, and globally accessed.

Of its five parameters, only the first three are required; the final two parameters are optional, used only in globally accessed contexts. Further parameter information appears in the parameter table and the usage notes.

Syntax

DBMS_SESSION.SET_CONTEXT (
   namespace VARCHAR2,
   attribute VARCHAR2,
   value     VARCHAR2,
   username  VARCHAR2,
   client_id VARCHAR2 );

Parameters

Usage Notes

Note the following:

• For 8i compatibility, only the first three parameters are used.

• The first three parameters are required for all types of context.

• The username parameter must be a valid SQL identifier

• The client_id parameter must be a string of at most 64 bytes. It is case-sensitive and must match the argument provided for set_identifier.

• If the namespace parameter is a global context namespace, then the username parameter is matched against the current database user name in the session, and the client_id parameter will be matched against the current client_id in the session. If these parameters are not set, NULL is assumed, enabling any user to see the context values.

• This procedure must be invoked directly or indirectly by the trusted package

• The caller of SET_CONTEXT must be in the calling stack of a procedure that has been associated to the context namespace through a CREATE CONTEXT statement. The checking of the calling stack does not cross a DBMS boundary.

• No limit applies to the number of attributes that can be set in a namespace. An attribute retains its value during the user's session unless it is reset by the user.

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SET_IDENTIFIER

This procedure sets the client ID in the session.

Syntax

DBMS_SESSION.SET_IDENTIFIER (
   client_id VARCHAR2);

Parameters

Usage Notes

Note the following:

• SET_IDENTIFIER initializes the current session with a client identifier to identify the associated global application context

• client_id is case sensitive; it must match the client_id parameter in the set_context

• This procedure is executable by public

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SET_NLS Procedure

This procedure sets up your Globalization Support (NLS). It is equivalent to the following SQL statement:

ALTER SESSION SET <nls_parameter> = <value>

Syntax

DBMS_SESSION.SET_NLS (
   param VARCHAR2, 
   value VARCHAR2);

Parameters

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SET_ROLE Procedure

This procedure enables and disables roles. It is equivalent to the SET ROLE SQL statement.

Syntax

DBMS_SESSION.SET_ROLE (
   role_cmd VARCHAR2);

Parameters

Usage Notes

Note that the procedure creates a new transaction if it is not invoked from within an existing transaction.

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SET_SQL_TRACE Procedure

This procedure turns tracing on or off. It is equivalent to the following SQL statement:

ALTER SESSION SET SQL_TRACE ...

Syntax

DBMS_SESSION.SET_SQL_TRACE (
   sql_trace boolean);

Parameters

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SWITCH_CURRENT_CONSUMER_GROUP Procedure

This procedure changes the current resource consumer group of a user's current session.

This lets you switch to a consumer group if you have the switch privilege for that particular group. If the caller is another procedure, then this enables the user to switch to a consumer group for which the owner of that procedure has switch privilege.

Syntax

DBMS_SESSION.switch_current_consumer_group (
   new_consumer_group     IN  VARCHAR2, 
   old_consumer_group     OUT VARCHAR2, 
   initial_group_on_error IN  BOOLEAN); 

Parameters

Return Values

This procedure outputs the old consumer group of the user in the parameter old_consumer_group.

Exceptions

Usage Notes

The owner of a procedure must have privileges on the group from which a user was switched (old_consumer_group) in order to switch them back. There is one exception: The procedure can always switch the user back to his/her initial consumer group (skipping the privilege check).

By setting initial_group_on_error to TRUE, SWITCH_CURRENT_CONSUMER_GROUP puts the current session into the default group, if it can't put it into the group designated by new_consumer_group. The error associated with the attempt to move a session into new_consumer_group is raised, even though the current consumer group has been changed to the initial consumer group.

Examples

CREATE OR REPLACE PROCEDURE high_priority_task is 
   old_group varchar2(30); 
   prev_group varchar2(30); 
   curr_user varchar2(30);  
BEGIN 
  -- switch invoker to privileged consumer group. If we fail to do so, an 
  -- error will be thrown, but the consumer group will not change 
  -- because 'initial_group_on_error' is set to FALSE 
 
  dbms_session.switch_current_consumer_group('tkrogrp1', old_group, FALSE); 
  -- set up exception handler (in the event of an error, we do not want to 
  -- return to caller while leaving the session still in the privileged 
  -- group) 
 
  BEGIN 
    -- perform some operations while under privileged group 
 
  EXCEPTION 
    WHEN OTHERS THEN 
     -- It is possible that the procedure owner does not have privileges 
     -- on old_group. 'initial_group_on_error' is set to TRUE to make sure 
     -- that the user is moved out of the privileged group in such a 
     -- situation 
 
     dbms_session.switch_current_consumer_group(old_group,prev_group,TRUE); 
     RAISE; 
    END; 
 
  -- we've succeeded. Now switch to old_group, or if cannot do so, switch 
  -- to caller's initial consumer group 
 
  dbms_session.switch_current_consumer_group(old_group,prev_group,TRUE); 
END high_priority_task; 
/  

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UNIQUE_SESSION_ID Function

This function returns an identifier that is unique for all sessions currently connected to this database. Multiple calls to this function during the same session always return the same result.

Syntax

DBMS_SESSION.UNIQUE_SESSION_ID 
  RETURN VARCHAR2;

Pragmas

pragma restrict_references(unique_session_id,WNDS,RNDS,WNPS);

Return Values