8 Managing Scalable Platforms

Simple Local Transactions

Many applications work with only simple local transactions. In these applications, an implicit transaction is created when the application makes database changes. The only transaction-specific calls needed by such applications are:

• OCITransCommit() - to commit the transaction

• OCITransRollback() - to roll back the transaction

As soon as one transaction has been committed or rolled back, the next modification to the database creates a new implicit transaction for the application.

Only one implicit transaction can be active at any time on a service context. Attributes of the implicit transaction are opaque to the user.

If an application creates multiple sessions, each one can have an implicit transaction associated with it.

Global Transactions

Global transactions are necessary only in more sophisticated transaction-processing applications.

Transaction Branches

Within a single global transaction, Oracle supports both tightly coupled and loosely coupled relationships between a pair of branches.

• Tightly coupled branches share the same local transaction. In this case, the gtrid references a unique local transaction, and multiple branches point to that same transaction. The owner of the transaction is the branch that was created first.

• Loosely coupled branches use different local transactions. In this case the gtrid and bqual together map to a unique local transaction. Each branch points to a different transaction.

The flags parameter of OCITransStart() allows applications to pass OCI_TRANS_TIGHT or OCI_TRANS_LOOSE to specify the type of coupling.

A session corresponds to a user session, created with OCISessionBegin().

Figure 8-1 illustrates tightly coupled branches within an application. S1 and S2, are sessions, B1 and B2 are branches, and T is a transaction. The XIDs of the two branches share the same gtrid, because they are operating on the same transaction, but they have a different bqual, because they are on separate branches

Figure 8-1 Multiple Tightly Coupled Branches

Description of "Figure 8-1 Multiple Tightly Coupled Branches"

Figure 8-2 illustrates how a single session operates on different branches. The gtrid component of the XIDs are different, because they represent separate global transactions

Figure 8-2 Session Operating on Multiple Branches

Description of "Figure 8-2 Session Operating on Multiple Branches"

It is possible for a single session to operate on multiple branches that share the same transaction, but this scenario does not have much practical value.

See Also:

"OCITransStart()" for sample code demonstrating this scenario

Transaction Examples

Here is how to use the transaction OCI calls:

The following tables show series of OCI calls and other actions, along with their resulting behavior. For the sake of simplicity, not all parameters to these calls are listed; rather, the flow of calls which is being demonstrated.

The OCI Action column indicates what the OCI application is doing, or what call it is making. The XID column lists the transaction identifier, when necessary. The Flags column lists the values passed in the flags parameter. The Result column describes the result of the call.

Initialization Parameters

Two initialization parameters relate to the use of global transaction branches and migratable open connections:

• TRANSACTIONS - This parameter specifies the maximum number of global transaction branches in the entire system. In contrast, the maximum number of branches on a single global transaction is 8.

• OPEN_LINKS_PER_INSTANCE - This parameter specifies the maximum number of migratable open connections. Migratable open connections are used by global transactions to cache connections after committing a transaction.Contrast this with the OPEN_LINKS parameter, that controls the number of connections from a session and is not applicable to applications that use global transactions.

OCITransStart()

SQL UPDATE

OCITransCommit()

OCITransStart()

SQL UPDATE

OCITransDetach()

OCITransStart()

SQL UPDATE

OCITransPrepare()

OCITransCommit

OCITransStart()

SQL UPDATE

OCITransCommit()

OCITransStart()

SQL SELECT

OCITransCommit()

OCI Authentication Management

The OCISessionBegin() call authenticates a user against the server set in the service context handle. It must be the first call for any given server handle. OCISessionBegin() authenticates the user for access to the Oracle server specified by the server handle and the service context of the call: after OCIServerAttach() initializes a server handle, OCISessionBegin() must be called to authenticate the user for that server.

When OCISessionBegin() is called for the first time on a server handle, the user session may not be created in migratable mode (OCI_MIGRATE). After OCISessionBegin() has been called for a server handle, the application may call OCISessionBegin() again to initialize another user session handle with different or the same credentials and different or the same operation modes. If an application wants to authenticate a user in OCI_MIGRATE mode, the service handle must already be associated with a non-migratable user handle. The userid of that user handle becomes the ownership ID of the migratable user session. Every migratable session must have a non-migratable parent session.

• If the OCI_MIGRATE mode is not specified, then the user session context can be used only with the server handle used with the OCISessionBegin().

• If OCI_MIGRATE mode is specified, then the user authentication can be set with other server handles. However, the user session context may only be used with server handles that resolve to the same database instance. Security checking is performed during session switching.

A migratable session can switch to a different server handle only if the ownership ID of the session matches the userid of a non-migratable session currently connected to that same server.

OCI_SYSDBA, OCI_SYSOPER, and OCI_PRELIM_AUTH settings can only be used with a primary user session context.

A migratable session can be switched, or migrated, to a server handle within an environment represented by an environment handle. It can also migrate or be cloned, to a server handle in another environment in the same process, or in a different process in a different mode. To perform this migration, or cloning, you need to do the following:

1. Extract the session id from the session handle using OCI_ATTR_MIGSESSION. This is an array of bytes that must not be modified by the caller.

   See Also:

   "User Session Handle Attributes"

2. Transport this session id to another process.

3. In the new environment, create a session handle and set the session id using OCI_ATTR_MIGSESSION.

4. Execute OCISessionBegin(). The resulting session handle is fully-authenticated.

To provide credentials for a call to OCISessionBegin(), you must provide a valid user name and password pair for database authentication in the user session handle parameter. This involves using OCIAttrSet() to set the OCI_ATTR_USERNAME and OCI_ATTR_PASSWORD attributes on the user session handle. Then OCISessionBegin() is called with OCI_CRED_RDBMS.

When the user session handle is terminated using OCISessionEnd(), the user name and password attributes are changed and thus cannot be re-used in a future call to OCISessionBegin(). They must be reset to new values before the next OCISessionBegin() call.

Or, you can supply external credentials. No attributes need to be set on the user session handle before calling OCISessionBegin(). The credential type is OCI_CRED_EXT. If values have been set for OCI_ATTR_USERNAME and OCI_ATTR_PASSWORD, then these are ignored if OCI_CRED_EXT is used.

OCI Password Management

The OCIPasswordChange() call enables an application to modify a user's database password as necessary. This is particularly useful if a call to OCISessionBegin() returns an error message or warning indicating that a user's password has expired.

Applications can also use OCIPasswordChange() to establish a user authentication context, and to change the password. If OCIPasswordChange() is called with an uninitialized service context, it establishes a service context and authenticates the user's account using the old password, and then changes the password to the new password. If the OCI_AUTH flag is set, it leaves the user session initialized. Otherwise, the user session is cleared.

If the service context passed to OCIPasswordChange() is already initialized, then OCIPasswordChange() authenticates the given account using the old password and changes the password to the new password. In this case, no matter how the flag is set, the user session remains initialized.

Secure External Password Store

As an alternative for large-scale deployments where applications use password credentials to connect to databases, it is possible to store such credentials in a client-side Oracle wallet. An Oracle wallet is a secure software container that is used to store authentication and signing credentials.

Storing database password credentials in a client-side Oracle wallet eliminates the need to embed user names and passwords in application code, batch jobs, or scripts. This reduces the risk of exposing passwords in the clear in scripts and application code, and simplifies maintenance because you need not change your code each time user names and passwords change. In addition, not having to change application code also makes it easier to enforce password management policies for these user accounts.

When you configure a client to use the external password store, applications can use the following syntax to connect to databases that use password authentication:

CONNECT /@database_alias

Note that you need not specify database login credentials in this CONNECT statement. Instead your system looks for database login credentials in the client wallet.

OCI Session Management

Transaction servers that actively balance user load by multiplexing user sessions over a few server connections must group these connections into a server group. Oracle uses server groups to identify these connections so that sessions can be managed effectively and securely.

The attribute OCI_ATTR_SERVER_GROUP must be defined to specify the server group name using the OCIAttrSet() call:

OCIAttrSet ((dvoid *) srvhp, (ub4) OCI_HTYPE_SERVER, (dvoid *) group_name, 
            (ub4) strlen ((CONST char *) group_name), 
            (ub4) OCI_ATTR_SERVER_GROUP, errhp);

The server group name is an alphanumeric string not exceeding 30 characters. OCI_ATTR_SERVER_GROUP attribute must be set in the server context prior to creating the first non-migratable session that uses that context. After the session is created successfully and the connection to the server is established, the server group name cannot be changed.

All migratable sessions created on servers within a server group can only migrate to other servers in the same server group. Servers that terminate will get removed from the server group. New servers may be created within an existing server group at any time.

The use of server groups is optional. If no server group is specified, the server is created in a server group called DEFAULT.

The owner of the first non-migratable session created in a nondefault server group becomes the owner of the server group. All subsequent non-migratable sessions for any server in this server group must be created by the owner of the server group.

The server group feature is useful when dedicated servers are used. It has no effect on shared servers. All shared servers effectively belong to the server group DEFAULT.

OCI Attributes for Middle-Tier Applications

The following attributes allow you to specify the external name and initial privileges of a client. These credentials are used by applications as alternative means of identifying or authenticating the client.

OCISession *session_handle;
OCISvcCtx  *application_server_session_handle;
OCIError   *error_handle;
...
OCIAttrSet((dvoid *)session_handle, (ub4) OCI_HTYPE_SESSION, 
           (dvoid *)application_server_session_handle, (ub4) 0, 
           OCI_ATTR_PROXY_CREDENTIALS, error_handle);

/* Declarations */
...
OCIAttrSet((dvoid *)session_handle, (ub4) OCI_HTYPE_SESSION,
           (dvoid *)distinguished_name, (ub4) 0,
           OCI_ATTR_DISTINGUISHED_NAME, error_handle);

OCIAttrSet((dvoid *)session_handle, (ub4) OCI_HTYPE_SESSION, 
           (dvoid *)certificate, ub4 certificate_length, 
           OCI_ATTR_CERTIFICATE, error_handle);

OCIAttrSet((dvoid *)session_handle, (ub4) OCI_HTYPE_SESSION, 
           (dvoid *)role_array, (ub4) number_of_strings,
           OCI_ATTR_INITIAL_CLIENT_ROLES, error_handle);

OCIAttrSet((dvoid *)session_handle, (ub4) OCI_HTYPE_SESSION, 
           (dvoid *)"janedoe", (ub4)strlen("janedoe"),
           OCI_ATTR_CLIENT_IDENTIFIER, error_handle);

SELECT sys_context('userenv', 'client_identifier') FROM dual;

OCIAttrSet((dvoid *)session_handle, (ub4) OCI_HTYPE_SESSION, (dvoid *)password,
           (ub4)0, OCI_ATTR_PASSWORD, error_handle);

OCI Middle-Tier Example

Here is a middle-tier example:

...
*OCIEnv *environment_handle; 
OCIServer *data_server_handle; 
OCIError *error_handle; 
OCISvcCtx *application_server_service_handle; 
OraText *client_roles[2]; 
OCISession *first_client_session_handle, second_client_session_handle; 
...
/*
** General initialization and allocation of contexts. 
*/
 
(void) OCIInitialize((ub4) OCI_DEFAULT, (dvoid *)0,
                     (dvoid * (*)(dvoid *, size_t)) 0, 
                     (dvoid * (*)(dvoid *, dvoid *, size_t))0, 
                     (void (*)(dvoid *, dvoid *)) 0 ); 
(void) OCIEnvInit( (OCIEnv **) &environment_handle, OCI_DEFAULT, (size_t) 0,
                  (dvoid **) 0 ); 
(void) OCIHandleAlloc( (dvoid *) environment_handle, (dvoid **) &error_handle,
     OCI_HTYPE_ERROR, (size_t) 0, (dvoid **) 0); 
/* 
** Allocate and initialize the server and service contexts used by the
** application server. 
*/ 

(void) OCIHandleAlloc( (dvoid *) environment_handle, 
     (dvoid **)&data_server_handle, OCI_HTYPE_SERVER, (size_t) 0, (dvoid **) 0); 
(void) OCIHandleAlloc( (dvoid *) environment_handle, (dvoid **)
     &application_server_service_handle, OCI_HTYPE_SVCCTX, (size_t) 0, 
     (dvoid **) 0);  
(void) OCIAttrSet((dvoid *) application_server_service_handle,
     OCI_HTYPE_SVCCTX, (dvoid *) data_server_handle, (ub4) 0, OCI_ATTR_SERVER,
     error_handle); 
/* 
** Authenticate the application server. In this case, external authentication is
** being used. 
*/

(void) OCIHandleAlloc((dvoid *) environment_handle, 
     (dvoid **)&application_server_session_handle, (ub4) OCI_HTYPE_SESSION,
     (size_t) 0, (dvoid **) 0); 
checkerr(error_handle, OCISessionBegin(application_server_service_handle,
     error_handle, application_server_session_handle, OCI_CRED_EXT,
     OCI_DEFAULT)); 
/* 
** Authenticate the first client 
** Note that no password is specified by the 
** application server for the client as it is trusted. 
*/ 

(void) OCIHandleAlloc((dvoid *) environment_handle, 
     (dvoid **)&first_client_session_handle, (ub4) OCI_HTYPE_SESSION, 
     (size_t) 0,(dvoid **) 0); 
(void) OCIAttrSet((dvoid *) first_client_session_handle, 
     (ub4) OCI_HTYPE_SESSION, (dvoid *) "jeff", (ub4) strlen("jeff"),
     OCI_ATTR_USERNAME, error_handle); 
/* 
** In place of specifying a password, pass the session handle of the application
** server instead. 
*/ 

(void) OCIAttrSet((dvoid *) first_client_session_handle, 
     (ub4) OCI_HTYPE_SESSION, (dvoid *) application_server_session_handle, 
     (ub4) 0, OCI_ATTR_PROXY_CREDENTIALS, error_handle); 
(void) OCIAttrSet((dvoid *) first_client_session_handle, 
     (ub4) OCI_HTYPE_SESSION, (dvoid *) "jeff@VeryBigBank.com", 
     (ub4) strlen("jeff@VeryBigBank.com"), OCI_ATTR_EXTERNAL_NAME,
     error_handle); 
/* 
** Establish the roles that the application server can use as the client. 
*/
 
client_roles[0] = (OraText *) "TELLER"; 
client_roles[1] = (OraText *) "SUPERVISOR";
(void) OCIAttrSet((dvoid *) first_client_session_handle, 
     OCI_ATTR_INITIAL_CLIENT_ROLES, error_handle); 
checkerr(error_handle, OCISessionBegin(application_server_service_handle,
     error_handle, first_client_session_handle, OCI_CRED_PROXY, OCI_DEFAULT)); 
/* 
** To start a session as another client, the application server does the 
** following. It must be 
** noted this code is unchanged from the current way of doing session switching. 
*/

(void) OCIHandleAlloc((dvoid *) environment_handle, 
     (dvoid **)&second_client_session_handle, (ub4) OCI_HTYPE_SESSION, 
     (size_t) 0, (dvoid **) 0); 
(void) OCIAttrSet((dvoid *) second_client_session_handle, 
     (ub4) OCI_HTYPE_SESSION, (dvoid *) "mutt", (ub4) strlen("mutt"),
     OCI_ATTR_USERNAME, error_handle); 
(void) OCIAttrSet((dvoid *) second_client_session_handle, 
     (ub4) OCI_HTYPE_SESSION, (dvoid *) application_server_session_handle, 
     (ub4) 0, OCI_ATTR_PROXY_CREDENTIALS, error_handle); 
(void) OCIAttrSet((dvoid *) second_client_session_handle, 
     (ub4) OCI_HTYPE_SESSION, (dvoid *) "mutt@VeryBigBank.com", 
     (ub4) strlen("mutt@VeryBigBank.com"), OCI_ATTR_EXTERNAL_NAME,
     error_handle); 
/* 
** Note that the application server has not specified any initial roles to have
** as the second client. 
*/
 
checkerr(error_handle, OCISessionBegin(application_server_service_handle,
     error_handle, second_client_session_handle, OCI_CRED_PROXY, OCI_DEFAULT)); 
/* 
** To switch to the first user, the application server applies the session
** handle obtained by the first 
** OCISessionBegin() call. This is the same as is currently done. 
*/ 

(void) OCIAttrSet((dvoid *)application_server_service_handle, 
     (ub4) OCI_HTYPE_SVCCTX, (dvoid *)first_client_session_handle, 
     (ub4)0, (ub4)OCI_ATTR_SESSION, error_handle); 
/* 
** After doing some operations, the application server can switch to
** the second client. That 
** is be done by the following call: 
*/

(void) OCIAttrSet((dvoid *)application_server_service_handle, 
     (ub4) OCI_HTYPE_SVCCTX, 
     (dvoid *)second_client_session_handle, (ub4)0, (ub4)OCI_ATTR_SESSION,
     error_handle); 
/* 
** and then do operations as that client 
*/
...

End-to-End Application Tracing

Use the following attributes to measure server call time, not including server round trips. These attributes can also be set using the PL/SQL package DBMS_APPLICATION_INFO which incurs one round trip to the server. Using OCI to set the attributes does not incur a round trip.

boolean enable_call_time;
ub8 call_time;
...
enable_call_time = TRUE;
OCIAttrSet(session, OCI_HTYPE_SESSION, (dvoid *)&enable_call_time,
           (ub4)0, OCI_ATTR_COLLECT_CALL_TIME,
           (OCIError *)error_handle);
OCIStmtExecute(...);
OCIAttrGet(session, OCI_HTYPE_SESSION, (dvoid *)&call_time,
           (ub4)0, OCI_ATTR_CALL_TIME, 
           (OCIError *)error_handle);
...

Externally Initialized Context Attributes in OCI

The client applications you develop can set application contexts explicitly in the session handle before authentication, using the following attributes in OCI functions:

OCIAttrSet(session, (ub4) OCI_HTYPE_SESSION, 
           (dvoid *)&size, (ub4)0, OCI_ATTR_APPCTX_SIZE, error_handle); 

OCIAttrGet(session, (ub4) OCI_HTYPE_SESSION, 
           (dvoid *)&ctxl_desc, (ub4)0, OCI_ATTR_APPCTX_LIST, error_handle);

OCIParamGet(ctxl_desc, OCI_DTYPE_PARAM, error_handle,(dvoid **)&ctx_desc, i);

OCIAttrSet(ctx_desc, OCI_DTYPE_PARAM,
     (dvoid *)ctx_name, sizeof(ctx_name), OCI_ATTR_APPCTX_NAME, error_handle);
  
OCIAttrSet(ctx_desc, OCI_DTYPE_PARAM,
     (dvoid *)attr_name, sizeof(attr_name), OCI_ATTR_APPCTX_ATTR, error_handle);  
  
OCIAttrSet(ctx_desc, OCI_DTYPE_PARAM,
     (dvoid *)value, sizeof(value), OCI_ATTR_APPCTX_VALUE, error_handle);  

Using OCISessionBegin() with an Externally initialized Context

When you call OCISessionBegin(), the context set in the session handle will be pushed to the server. No additional contexts are propagated to the server session. Here is a code example to illustrate use of these calls and attributes:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <oci.h>

static OraText *username = (OraText *) "HR";
static OraText *password = (OraText *) "HR";

static OCIEnv *envhp;
static OCIError *errhp;

int main(/*_ int argc, char *argv[] _*/);

static sword status;

int main(argc, argv)
int argc;
char *argv[];
{

  OCISession *authp = (OCISession *) 0;
  OCIServer *srvhp;
  OCISvcCtx *svchp;
  OCIDefine *defnp = (OCIDefine *) 0;
  dvoid     *parmdp;
  ub4        ctxsize;
  OCIParam  *ctxldesc;
  OCIParam  *ctxedesc;

  OCIEnvCreate(&envhp, OCI_DEFAULT, (dvoid *)0, 0, 0, 0,
                            (size_t)0, (dvoid *)0);

  (void) OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &errhp, OCI_HTYPE_ERROR,
                   (size_t) 0, (dvoid **) 0);

  /* server contexts */
  (void) OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &srvhp, OCI_HTYPE_SERVER,
                   (size_t) 0, (dvoid **) 0);

  (void) OCIHandleAlloc( (dvoid *) envhp, (dvoid **) &svchp, OCI_HTYPE_SVCCTX,
                   (size_t) 0, (dvoid **) 0);

  (void) OCIServerAttach( srvhp, errhp, (OraText *)"", strlen(""), 0);

  /* set attribute server context in the service context */
  (void) OCIAttrSet( (dvoid *) svchp, OCI_HTYPE_SVCCTX, (dvoid *)srvhp,
                    (ub4) 0, OCI_ATTR_SERVER, (OCIError *) errhp);

  (void) OCIHandleAlloc((dvoid *) envhp, (dvoid **)&authp,
                        (ub4) OCI_HTYPE_SESSION, (size_t) 0, (dvoid **) 0);
/****************************************/
  /* set app ctx size to 2 because we want to set up 2 application contexts */
  ctxsize = 2;

  /* set up app ctx buffer */
  (void) OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION,
                 (dvoid *) &ctxsize, (ub4) 0,
                 (ub4) OCI_ATTR_APPCTX_SIZE, errhp);

  /* retrieve the list descriptor */
  (void) OCIAttrGet((dvoid *)authp, (ub4) OCI_HTYPE_SESSION,
                    (dvoid *)&ctxldesc, 0, OCI_ATTR_APPCTX_LIST, errhp );

  /* retrieve the 1st ctx element descriptor */
  (void) OCIParamGet(ctxldesc, OCI_DTYPE_PARAM, errhp, (dvoid**)&ctxedesc, 1);

  (void) OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) "HR", (ub4) strlen((char *)"HR"),
                 (ub4) OCI_ATTR_APPCTX_NAME, errhp);

  (void) OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) "ATTR1", (ub4) strlen((char *)"ATTR1"),
                 (ub4) OCI_ATTR_APPCTX_ATTR, errhp);

  (void) OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) "VALUE1", (ub4) strlen((char *)"VALUE1"),
                 (ub4) OCI_ATTR_APPCTX_VALUE, errhp);

  /* set second context */
  (void) OCIParamGet(ctxldesc, OCI_DTYPE_PARAM, errhp, (dvoid**)&ctxedesc, 2);

  (void) OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) "HR", (ub4) strlen((char *)"HR"),
                 (ub4) OCI_ATTR_APPCTX_NAME, errhp);

  (void) OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) "ATTR2", (ub4) strlen((char *)"ATTR2"),
                 (ub4) OCI_ATTR_APPCTX_ATTR, errhp);

  (void) OCIAttrSet((dvoid *) ctxedesc, (ub4) OCI_DTYPE_PARAM,
                 (dvoid *) "VALUE2", (ub4) strlen((char *)"VALUE2"),
                 (ub4) OCI_ATTR_APPCTX_VALUE, errhp);
/****************************************/
  (void) OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION,
                 (dvoid *) username, (ub4) strlen((char *)username),
                 (ub4) OCI_ATTR_USERNAME, errhp);

  (void) OCIAttrSet((dvoid *) authp, (ub4) OCI_HTYPE_SESSION,
                 (dvoid *) password, (ub4) strlen((char *)password),
                 (ub4) OCI_ATTR_PASSWORD, errhp);

  OCISessionBegin ( svchp,  errhp, authp, OCI_CRED_EXT, (ub4) OCI_DEFAULT);

}

Multiple SET Operations

Use OCIAppCtxSet() to perform a series of set operations on 'responsibility' attribute in the CLIENTCONTEXT namespace. When this information is sent to the server, the latest value will prevail for that particular attribute in a namespace. To change the value of the 'responsibility' attribute in the CLIENTCONTEXT namespace from 'manager' to 'vp', use the code snippet shown next, on the client side. When this information is transported to the server, the server will show the latest value 'vp' for the 'responsibility' attribute in the CLIENTCONTEXT namespace.

err = OCIAppCtxSet((void *) sesshndl,(dvoid *)"CLIENTCONTEXT",(ub4) 13,
                   (dvoid *)"responsibility", 14
                   (dvoid *)"manager", 7, errhp, OCI_DEFAULT);
err = OCIAppCtxSet((void *) sesshndl, (dvoid*)"CLIENTCONTEXT", 13,
                   (dvoid *)"responsibility", 14,(dvoid *)"vp",2, errhp,
                   OCI_DEFAULT);

You can clear specific attribute information in a client namespace. This can be done by setting the value of an attribute to NULL or an empty string, using the OCIAppCtxSet() function:

(void) OCIAppCtxSet((void *) sesshndl, (dvoid *)"CLIENTCONTEXT", 13,
                    (dvoid *)"responsibility", 14, (dvoid *)0, 0,errhp,
                    OCI_DEFAULT);

or:

(void) OCIAppCtxSet((void *) sesshndl, (dvoid *)"CLIENTCONTEXT", 13
                    (dvoid *)"responsibility", 14, (dvoid *)"", 0,errhp,
                     OCI_DEFAULT);

CLEAR-ALL Operations Between SET Operations

You can clear all the context information in a specific client namespace, using the OCIAppCtxClearAll() function and it will also be cleared on the server-side user session, during the next network transport.

If the client application performs a clear-all operation in a namespace after a couple of set operations, then values of all attributes in that namespace that were set prior to this clear-all operation are cleaned up on the client side and the server side. Only the subsequent set operations that were done after the clear-all operation, are reflected on the server side. On the client side:

err = OCIAppCtxSet((void *) sesshndl,(dvoid *)"CLIENTCONTEXT", 13,
                   (dvoid *)"responsibility", 14,
                   (dvoid *)"manager", 7,errhp, OCI_DEFAULT);
err = OCIAppCtxClearAll((void *) sesshndl, (dvoid *)"CLIENTCONTEXT", 13, errhp,
                        OCI_DEFAULT);
err = OCIAppCtxSet((void *) sesshndl, (dvoid*)"CLIENTCONTEXT",13
                   (dvoid *)"office",6, (dvoid *)"2op123", 5, errhp, OCI_DEFAULT);

The clear-all operation will clear up any information set by earlier operations in the namespace CLIENTCONTEXT: 'responsibility' = 'manager' is cleaned up. The information that was set subsequently will be reflected on the server side.

Network Transport and PL/SQL on Client Namespace

It is possible that an application could send application context information on a OCIStmtExecute() call to the server, and also attempt to change the same context information during that call by executing the DBMS_SESSION package.

In general, on the server side, the transported information is processed first and the main call is processed later. This behavior will apply to the application context network transports as well.

If they are both writing to the same client namespace and attribute set, then the main call's information will overwrite the information set by the fast network transport mechanism. Please note that in case of an error in the network transport call, the main call will not be executed.

Note that an error in the main call will not affect the processing of the network transport call. Once the network transport is processed then there is no way to undo it, based on errors in the main call. When the error is reported to the caller (by an OCI function), it is reported as a generic ORA error. Currently, there is no easy way to distinguish an error in the network transport from an error in the main call. The client should not make any assumptions that an error from main call will undo the round trip network processing and implement appropriate exception-handling mechanisms to prevent any inconsistencies.