17. Deferred Transactions and Remote Procedure Calls

Contents:
About Deferred Transactions and RPCs
DBMS_DEFER_SYS: Managing Deferred Transactions
DBMS_DEFER: Building Deferred Calls
DBMS_DEFER_QUERY: Performing Diagnostics and Maintenance

Oracle's advanced replication option relies primarily on deferred transactions and remote procedure calls (RPCs). When you commit a transaction against a replicated table, for example, the replication support triggers queue a deferred transaction to do your bidding in one or more remote databases. In addition to providing many of the underpinnings for the advanced replication option, the packages used to create and manipulate deferred calls are available for direct use in your applications. You will use the packages described in this chapter for deferred transactions and RPCs.

DBMS_DEFER_SYS: Performs administrative tasks such as scheduling, executing, and deleting queued transactions.
DBMS_DEFER: Builds deferred calls.
DBMS_DEFER_QUERY: Provides access to parameters passed to deferred calls, primarily for diagnostic purposes.

NOTE: Users must have explicit EXECUTE privileges on DBMS_DEFER in order to create deferred calls.

17.1 About Deferred Transactions and RPCs

This section provides some basic information you'll find useful in using the packages described in this chapter.

17.1.1 About Remote Destinations

Every remote procedure call has to be executed somewhere , and Oracle offers several methods of specifying where.

If you are using the advanced replication option, you have implicitly named the destinations for deferred RPCs and transactions by creating master sites. Whenever a user performs DML on a table, the transaction is applied locally and is queued for delivery to all other sites where the table is replicated; these sites are listed in the DBA_REPSITES data dictionary view. Similarly, replicated procedure calls are also queued for all master sites in the replicated environment. Refer to Chapter 15, Advanced Replication , for details on using DBMS_REPCAT, which performs most replicated environment administration operations.

If you are not using the advanced replication option, then the destination site(s) are determined by one of the following means, listed in order of precedence:

The sites specified in the nodes parameter in the call to DBMS_DEFER.CALL, described later in this chapter.
The sites specified in the nodes parameter to DBMS_DEFER.TRANSACTION, described later in this chapter.
The sites specified in the DEFDEFAULTDEST data dictionary view, described later in this chapter ( Table 17.4 ).

If Oracle cannot determine a call's destination by any of these methods, or if you specify differing destinations in the DBMS_DEFER.TRANSACTION and DBMS_DEFER.CALL procedures, the deferred call will raise an exception.

17.1.2 Data Dictionary Views

There are eight data dictionary views (see Table 17.1 ) that contain data about deferred transactions and RPCs. You can query these views to determine information such as the destination of RPC calls, error messages, and scheduled execution times. Most of the packages associated with deferred calls reference and/or modify the data in these views.

Tables 17-2 through 17-9 provide details about the contents of these views.

Table 17.1: Data Dictionary Views Associated with Deferred Calls
View Name	Description
DEFCALL	Contains information about all deferred RPCs. Queries SYSTEM.DEF$_CALL table.
DEFCALLDEST	Contains the destination database(s) for each deferred RPC in DEFCALL. Queries SYSTEM.DEF$_CALL, SYSTEM.DEF$_DESTINATION, SYSTEM.DEF$_CALLDEST, SYSTEM.DEF$_ERROR, and SYSTEM.REPCAT$_REPPROP.
DEFDEFAULTDEST	Contains the default destinations for deferred RPCs. Queries SYSTEM.DEF$_DEFAULTDEST.
DEFERROR	Contains error information for deferred calls that could not be applied at their destination. Queries SYSTEM. DEF$_ERROR.
DEFERRORCOUNT	Contains the count of errors for each destination. Queries SYSTEM.DEF$_ERROR.
DEFSCHEDULE	Contains information about the scheduling of deferred jobs. Queries SYSTEM.DEF$_DESTINATION and SYS.JOB$.
DEFTRAN	Contains information about all deferred calls. Queries SYSTEM.DEF$_CALL and SYS.USER$.
DEFTRANDEST	Contains the destination database(s) for each deferred transaction. Queries SYSTEM.DEF$_CALL, SYSTEM.DEF$_DESTINATION, SYSTEM.DEF$_ERROR, SYSTEM.DEF$_CALLDEST, and SYSTEM.REPCAT$_REPPROP.

Table 17.2: Columns in DEFCALL Data Dictionary View
Column Name	Description
CALLNO	Unique ID of call at deferred_tran_db
DEFERRED_TRAN_DB	Global name of database that originated the call
DEFERRED_TRAN_ID	Unique ID of the transaction
SCHEMANAME	Schema that owns the package
PACKAGENAME	Name of the package
PROCNAME	Name of the procedure within the package
ARGCOUNT	Number of arguments passed to the procedure

Table 17.3: Columns in DEFCALLDEST Data Dictionary View
Column Name	Description
CALLNO	Unique ID of call at deferred_tran_db.
DEFERRED_TRAN_ID	Unique ID of the transaction. Note that each deferred_tran_id has one or more calls.
DEFERRED_TRAN_DB	Global name of database that originated the call.
DBLINK	Global name of the destination database.

Table 17.4: Columns in DEFDEFAULTDEST Data Dictionary View
Column Name	Description
DBLINK	Global name of the destination database

Table 17.5: Columns in DEFERROR Data Dictionary View
Column Name	Description
DEFERRED_TRAN_DB	Global name of the database that originated the RPC
DEFERRED_TRAN_ID	ID of the transaction originating or copying the deferred RPC
CALLNO	Unique ID of call at deferred_tran_db
DESTINATION	Database link used to specify the destination database
ERROR_TIME	Time the error occurred
ERROR_NUMBER	Oracle error number
ERROR_MSG	Error message text

Table 17.6: Columns in DEFERRCOUNT Data Dictionary View
Column Name	Description
ERRCOUNT	Number of errors in deferred RPC calls to destination
DESTINATION	Global name of destination database

Table 17.7: Columns in DEFSCHEDULE Data Dictionary View
Column Name	Description
DBLINK	Global name of the database for which pushes of deferred RPC calls is scheduled
JOB	Number of the job (job column in DBA_JOBS)
INTERVAL	Date expression that determines how often the job runs
NEXT_DATE	Next time the job is scheduled to run
LAST_DATE	Last time the job ran
DISABLED	Y if propagation to destination is disabled, otherwise N
LAST_TXN_COUNT	Number of transactions pushed last time job ran
LAST_ERROR	Oracle error number from the most recent push
LAST_MSG	Error message text from the most recent push

Table 17.8: Columns in DEFTRAN Data Dictionary View
Column Name	Description
DEFERRED_TRAN_ID	ID of the transaction that originated or copied the deferred RPCs.
DEFERRED_TRAN_DB	Global name of the database that originated or copied the deferred RPCs.
ORIGIN_TRAN_ID	ID of the transaction that originated the deferred RPCs.
ORIGIN_TRAN_DB	Global name of the database that originated the deferred RPCs.
ORIGIN_USER	USERID of user originating deferred RPC calls.
DELIVERY_ORDER	SCN of the deferred transaction in the queue.
DESTINATION_LIST	R if destinations are determined by the DBA_REPSCHEMA data dictionary view. D if destinations were specified in DEFDEFAULTDEST or the NODE_LIST parameter to the DBMS_DEFER.TRANSACTION, DBMS_DEFER.CALL, or DBMS_DEFER.COPY procedures.
START_TIME	Start time of the origination transaction.
COMMIT_COMMENT	User-supplied comments.

Table 17.9: Columns in DEFTRANDEST Data Dictionary View
Column Name	Description
DEFERRED_TRAN_ID	ID of the transaction to propagate to database specified by dblink
DEFERRED_TRAN_DB	Global name of the database that originated the deferred transaction
DBLINK	Global name of the destination database