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:
Security Model
Operational Notes
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.
Table 96-1 DBMS_SESSION Package Subprograms
Subprogram | Description |
---|---|
Clears all context information |
|
Clears the context |
|
Clears the identifier |
|
Closes database link |
|
Lets you reclaim unused memory after performing operations requiring large amounts of memory |
|
Determines if the named role is enabled for the session. |
|
Determines if the specified session is active |
|
Returns a list of active namespace and context for the current session |
|
Resets the session-level SQL trace for the session from which it was called. |
|
Enables session-level SQL trace for the invoking session |
|
De-instantiates all packages in the session |
|
Sets or resets the value of a context attribute |
|
Sets the identifier |
|
Sets Globalization Support (NLS) |
|
Sets role |
|
Turns tracing on or off |
|
Facilitates changing the current resource consumer group of a user's current session |
|
Returns an identifier that is unique for all sessions currently connected to this database |
DBMS_SESSION.CLEAR_ALL_CONTEXT namespace VARCHAR2);
Table 96-2 CLEAR_ALL_CONTEXT Procedure Parameters
Parameter | Description |
---|---|
|
The namespace where the application context information is to be cleared. Required. |
This procedure must be invoked directly or indirectly by the trusted package.
DBMS_SESSION.CLEAR_CONTEXT namespace VARCHAR2, client_identifier VARCHAR2 attribute VARCHAR2);
Table 96-3 CLEAR_CONTEXT Procedure Parameters
Parameter | Description |
---|---|
|
The namespace in which the application context is to be cleared. Required. For a session-local context, For a globally accessed context, |
|
Applies to a global context and is optional for other types of contexts; 64-byte maximum. |
|
The specific attribute in the namespace to be cleared. Optional. the default is |
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);
Table 96-4 CLOSE_DATABASE_LINK Procedure Parameters
Parameter | Description |
---|---|
|
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:
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.
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:
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.
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;
Table 96-6 IS_ROLE_ENABLED Function Return Values
Return | Description |
---|---|
|
|
This function determines if the specified session is active.
DBMS_SESSION.IS_SESSION_ALIVE ( uniqueid VARCHAR2) RETURN BOOLEAN;
Table 96-7 IS_SESSION_ALIVE Function Parameters
Parameter | Description |
---|---|
|
Unique ID of the session: This is the same one as returned by |
Table 96-8 IS_SESSION_ALIVE Function Return Values
Return | Description |
---|---|
|
|
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);
Table 96-9 LIST_CONTEXT Procedure Parameters
Parameter | Description |
---|---|
|
Buffer to store a list of application context set in the current session. |
Table 96-10 LIST_CONTEXT Procedure Return Values
Return | Description |
---|---|
|
A list of (namespace, attribute, values) set in current session. |
|
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 96-12.
DBMS_SESSION.MODIFY_PACKAGE_STATE( action_flags IN PLS_INTEGER);
Table 96-11 MODIFY_PACKAGE_STATE Procedure Parameters
Parameter | Description |
---|---|
|
Bit flags that determine the action taken on PL/SQL program units:
However,
|
See the parameter descriptions in Table 96-13 for the differences between the flags and why DBMS_SESSION.REINITIALIZE
exhibits better performance than DBMS_SESSION.FREE_ALL_RESOURCES
.
Table 96-12 Action_flags Constants for MODIFY_PACKAGE_STATE
Constant | Description |
---|---|
|
|
|
|
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.
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 resets the session-level SQL trace for the session from which it was called. Client ID and service/module/action traces are not affected.
DBMS_SESSION.SESSION_TRACE_ENABLE();
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.
DBMS_SESSION.SESSION_TRACE_ENABLE( waits IN BOOLEAN DEFAULT TRUE,�� binds IN BOOLEAN DEFAULT FALSE);�
Table 96-13 SESSION_TRACE_ENABLE Procedure Parameters
Parameter | Description |
---|---|
|
Specifies if wait information is to be traced |
binds |
Specifies if bind information is to be traced |
This procedure de-instantiates all packages in this session. It frees the package state.
Note:
See "SESSION _TRACE_ENABLE Procedure" . The MODIFY_PACKAGE_STATE interface, introduced in Oracle9i, provides an equivalent of the RESET_PACKAGE capability. It is an efficient, lighter-weight variant for reinitializing the state of all PL/SQL packages in the session.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.
Note:
RESET_PACKAGE
only frees the memory, cursors, and package variables after the PL/SQL call that made the invocation finishes running.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 );
Table 96-14 SET_CONTEXT Procedure Parameters
Parameter | Description |
---|---|
|
The namespace of the application context to be set, limited to 30 bytes. |
|
The attribute of the application context to be set, limited to 30 bytes. |
|
The value of the application context to be set, limited to 4 kilobytes. |
|
The database username attribute of the application context. Default: NULL |
|
The application-specific client_id attribute of the application context (64-byte maximum). Default: NULL |
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.
This procedure sets the client ID in the session.
DBMS_SESSION.SET_IDENTIFIER ( client_id VARCHAR2);
Table 96-15 SET_IDENTIFIER Procedure Parameters
Parameter | Description |
---|---|
|
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 context
client_id
is case sensitive; it must match the client_id
parameter in the set_context
This procedure is executable by public
This 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);
Table 96-16 SET_NLS Procedure Parameters
Parameter | Description |
---|---|
|
Globalization Support parameter. The parameter name must begin with 'NLS'. |
|
Parameter value. If the parameter is a text literal, then it needs embedded single-quotes. For example, " |
This procedure enables and disables roles. It is equivalent to the SET
ROLE
SQL statement.
DBMS_SESSION.SET_ROLE ( role_cmd VARCHAR2);
Table 96-17 SET_ROLE Procedure Parameters
Parameter | Description |
---|---|
|
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);
Table 96-18 SET_SQL_TRACE Procedure Parameters
Parameter | Description |
---|---|
|
|
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);
Table 96-19 SWITCH_CURRENT_CONSUMER_GROUP Procedure Parameters
Parameter | Description |
---|---|
|
Name of consumer group to which you want to switch. |
|
Name of the consumer group from which you just switched out. |
|
If |
This procedure outputs the old consumer group of the user in the parameter old_consumer_group
.
Note:
You can switch back to the old consumer group later using the value returned inold_consumer_group
.Table 96-20 SWITCH_CURRENT_CONSUMER_GROUP Procedure Exceptions
Exception | Description |
---|---|
|
Non-existent consumer group. |
|
Insufficient privileges. |
|
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; /
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);