| PL/SQL Packages and Types Reference 10g Release 1 (10.1) Part Number B10802-01 |
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| PL/SQL Packages and Types Reference 10g Release 1 (10.1) Part Number B10802-01 |
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This package provides access to SQL ALTER SESSION and SET ROLE statements, and other session information, from PL/SQL. You can use DBMS_SESSION to set preferences and security levels.
This chapter contains the following topics:
This package runs with the privileges of the calling user, rather than the package owner SYS.
You should not attempt to turn close_cached_open_cursors on or off.
DBMS_SESSION.CLEAR_CONTEXT namespace VARCHAR2, client_identifier VARCHAR2 attribute VARCHAR2);
This procedure must be invoked directly or indirectly by the trusted package.
DBMS_SESSION.CLEAR_ALL_CONTEXT namespace VARCHAR2);
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The namespace where the application context information is to be cleared. Required. |
This procedure must be invoked directly or indirectly by the trusted package.
This procedure removes the set_client_id in the session.
DBMS_SESSION.CLEAR_IDENTIFIER;
This procedure is executable by public.
This procedure closes an open database link. It is equivalent to the following SQL statement:
ALTER SESSION CLOSE DATABASE LINK <name>
DBMS_SESSION.CLOSE_DATABASE_LINK ( dblink VARCHAR2);
| Parameter | Description |
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Name of the database link to close. |
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:
sort_area_size is used and sort_area_size is hundreds of KB.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.
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Note: This procedure should only be used in cases where memory is at a premium. It should be used infrequently and judiciously. |
DBMS_SESSION.FREE_UNUSED_USER_MEMORY;
The behavior of this procedure depends upon the configuration of the server operating on behalf of the client:
shared_pool. Session memory is allocated from the shared_pool in this configuration.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.
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;
This function determines if the named role is enabled for this session.
DBMS_SESSION.IS_ROLE_ENABLED ( rolename VARCHAR2) RETURN BOOLEAN;
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Name of the role. |
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This function determines if the specified session is active.
DBMS_SESSION.IS_SESSION_ALIVE ( uniqueid VARCHAR2) RETURN BOOLEAN;
| Parameter | Description |
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Unique ID of the session: This is the same one as returned by |
| Return | Description |
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This procedure returns a list of active namespaces and contexts for the current session.
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);
| Parameter | Description |
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Buffer to store a list of application context set in the current session. |
| Return | Description |
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A list of (namespace, attribute, values) set in current session. |
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Returns the number of entries in the buffer returned. |
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.
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 86-12.
DBMS_SESSION.MODIFY_PACKAGE_STATE( action_flags IN PLS_INTEGER);
See the parameter descriptions in Table 86-11 for the differences between the flags and why DBMS_SESSION.REINITIALIZE exhibits better performance than DBMS_SESSION.FREE_ALL_RESOURCES.
| Constant | Description |
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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:
FREE_ALL_RESOURCES or REINITIALIZE, make sure that resetting package variable values does not affect the application.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).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.
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.
This procedure deinstantiates all packages in this session. It frees the package state.
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Note: See "MODIFY_PACKAGE_STATE Procedure" . The |
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.
DBMS_SESSION.RESET_PACKAGE;
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.
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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).
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;
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.
DBMS_SESSION.SET_CONTEXT ( namespace VARCHAR2, attribute VARCHAR2, value VARCHAR2, username VARCHAR2, client_id VARCHAR2 );
Note the following:
username parameter must be a valid SQL identifierclient_id parameter must be a string of at most 64 bytes. It is case-sensitive and must match the argument provided for set_identifier.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.CREATE CONTEXT statement. The checking of the calling stack does not cross a DBMS boundary.This procedure sets the client ID in the session.
DBMS_SESSION.SET_IDENTIFIER ( client_id VARCHAR2);
| Parameter | Description |
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The application-specific identifier of the current database session. |
Note the following:
SET_IDENTIFIER initializes the current session with a client identifier to identify the associated global application contextclient_id is case sensitive; it must match the client_id parameter in the set_contextThis procedure sets up your Globalization Support (NLS). It is equivalent to the following SQL statement:
ALTER SESSION SET <nls_parameter> = <value>
DBMS_SESSION.SET_NLS ( param VARCHAR2, value VARCHAR2);
This procedure enables and disables roles. It is equivalent to the SET ROLE SQL statement.
DBMS_SESSION.SET_ROLE ( role_cmd VARCHAR2);
| Parameter | Description |
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This text is appended to "set role" and then run as SQL. |
This procedure turns tracing on or off. It is equivalent to the following SQL statement:
ALTER SESSION SET SQL_TRACE ...
DBMS_SESSION.SET_SQL_TRACE ( sql_trace boolean);
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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.
DBMS_SESSION.switch_current_consumer_group ( new_consumer_group IN VARCHAR2, old_consumer_group OUT VARCHAR2, initial_group_on_error IN BOOLEAN);
This procedure outputs the old consumer group of the user in the parameter old_consumer_group.
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Note: You can switch back to the old consumer group later using the value returned in |
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.
DBMS_SESSION.UNIQUE_SESSION_ID RETURN VARCHAR2;
pragma restrict_references(unique_session_id,WNDS,RNDS,WNPS);
| Return | Description |
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Returns up to 24 bytes. |
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Non-existent consumer group. |
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Insufficient privileges. |
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Cannot switch to |
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.
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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