Handlers and Row LCR Processing

Nel documento Oracle® Streams Replication Administrator’s Guide 10g (pagine 39-42)

Any of the following handlers can process a row LCR:

DML handler

Error handler

Update conflict handler

The following sections describe the possible scenarios involving these handlers:

No Relevant Handlers

Relevant Update Conflict Handler

DML Handler But No Relevant Update Conflict Handler

DML Handler And a Relevant Update Conflict Handler

Error Handler But No Relevant Update Conflict Handler

Error Handler And a Relevant Update Conflict Handler

You cannot have a DML handler and an error handler simultaneously for the same operation on the same table. Therefore, there is no scenario in which they could both be invoked.

No Relevant Handlers If there are no relevant handlers for a row LCR, then an apply process tries to apply the change specified in the row LCR directly. If the apply process can apply the row LCR, then the change is made to the row in the table. If there is a conflict or an error during apply, then the transaction containing the row LCR is rolled back, and all of the LCRs in the transaction that should be applied according to the apply process rule sets are moved to the error queue.

Relevant Update Conflict Handler Consider a case where there is a relevant update conflict handler configured, but no other relevant handlers are configured. An apply process tries to apply the change specified in a row LCR directly. If the apply process can apply the row LCR, then the change is made to the row in the table.

If there is an error during apply that is caused by a condition other than an update conflict, including a uniqueness conflict or a delete conflict, then the transaction containing the row LCR is rolled back, and all of the LCRs in the transaction that should be applied according to the apply process rule sets are moved to the error queue.

If there is an update conflict during apply, then the relevant update conflict handler is invoked. If the update conflict handler resolves the conflict successfully, then the apply process either applies the LCR or discards the LCR, depending on the resolution of the update conflict, and the apply process continues applying the other LCRs in the transaction that should be applied according to the apply process rule sets. If the update conflict handler cannot resolve the conflict, then the transaction containing the row LCR is rolled back, and all of the LCRs in the transaction that should be applied according to the apply process rule sets are moved to the error queue.

See Also: Chapter 3, "Streams Conflict Resolution"

Apply and Streams Replication

DML Handler But No Relevant Update Conflict Handler Consider a case where an apply process passes a row LCR to a DML handler, and there is no relevant update conflict handler configured.

The DML handler processes the row LCR. The designer of the DML handler has complete control over this processing. Some DML handlers can perform SQL operations or run the EXECUTE member procedure of the row LCR. If the DML handler runs the EXECUTE member procedure of the row LCR, then the apply process tries to apply the row LCR. This row LCR might have been modified by the DML handler.

If any SQL operation performed by the DML handler fails, or if an attempt to run the EXECUTE member procedure fails, then the DML handler can try to handle the exception. If the DML handler does not raise an exception, then the apply process assumes the DML handler has performed the appropriate action with the row LCR, and the apply process continues applying the other LCRs in the transaction that should be applied according to the apply process rule sets.

If the DML handler cannot handle the exception, then the DML handler should raise an exception. In this case, the transaction containing the row LCR is rolled back, and all of the LCRs in the transaction that should be applied according to the apply process rule sets are moved to the error queue.

DML Handler And a Relevant Update Conflict Handler Consider a case where an apply process passes a row LCR to a DML handler and there is a relevant update conflict handler configured.

The DML handler processes the row LCR. The designer of the DML handler has complete control over this processing. Some DML handlers might perform SQL operations or run the EXECUTE member procedure of the row LCR. If the DML handler runs the EXECUTE member procedure of the row LCR, then the apply process tries to apply the row LCR. This row LCR could have been modified by the DML handler.

If any SQL operation performed by the DML handler fails, or if an attempt to run the EXECUTE member procedure fails for any reason other than an update conflict, then the behavior is the same as that described in "DML Handler But No Relevant Update Conflict Handler" on page 1-24. Note that uniqueness conflicts and delete conflicts are not update conflicts.

If an attempt to run the EXECUTE member procedure fails because of an update conflict, then the behavior depends on the setting of the conflict_resolution parameter in the EXECUTE member procedure:

The conflict_resolution Parameter Is Set to true

If the conflict_resolution parameter is set to true, then the relevant update conflict handler is invoked. If the update conflict handler resolves the conflict successfully, and all other operations performed by the DML handler succeed, then the DML handler finishes without raising an exception, and the apply process

continues applying the other LCRs in the transaction that should be applied according to the apply process rule sets.

If the update conflict handler cannot resolve the conflict, then the DML handler can try to handle the exception. If the DML handler does not raise an exception, then the apply process assumes the DML handler has performed the appropriate action with the row LCR, and the apply process continues applying the other LCRs in the

transaction that should be applied according to the apply process rule sets. If the DML handler cannot handle the exception, then the DML handler should raise an exception.

In this case, the transaction containing the row LCR is rolled back, and all of the LCRs

Apply and Streams Replication

in the transaction that should be applied according to the apply process rule sets are moved to the error queue.

The conflict_resolution Parameter Is Set to false

If the conflict_resolution parameter is set to false, then the relevant update conflict handler is not invoked. In this case, the behavior is the same as that described in "DML Handler But No Relevant Update Conflict Handler" on page 1-24.

Error Handler But No Relevant Update Conflict Handler Consider a case where an apply process encounters an error when it tries to apply a row LCR. This error can be caused by a conflict or by some other condition. There is an error handler for the table

operation but no relevant update conflict handler configured.

The row LCR is passed to the error handler. The error handler processes the row LCR.

The designer of the error handler has complete control over this processing. Some error handlers might perform SQL operations or run the EXECUTE member procedure of the row LCR. If the error handler runs the EXECUTE member procedure of the row LCR, then the apply process tries to apply the row LCR. This row LCR could have been modified by the error handler.

If any SQL operation performed by the error handler fails, or if an attempt to run the EXECUTE member procedure fails, then the error handler can try to handle the exception. If the error handler does not raise an exception, then the apply process assumes the error handler has performed the appropriate action with the row LCR, and the apply process continues applying the other LCRs in the transaction that should be applied according to the apply process rule sets.

If the error handler cannot handle the exception, then the error handler should raise an exception. In this case, the transaction containing the row LCR is rolled back, and all of the LCRs in the transaction that should be applied according to the apply process rule sets are moved to the error queue.

Error Handler And a Relevant Update Conflict Handler Consider a case where an apply process encounters an error when it tries to apply a row LCR. There is an error handler for the table operation, and there is a relevant update conflict handler configured.

The handler that is invoked to handle the error depends on the type of error it is:

If the error is caused by a condition other than an update conflict, including a uniqueness conflict or a delete conflict, then the error handler is invoked, and the behavior is the same as that described in "Error Handler But No Relevant Update Conflict Handler" on page 1-25.

If the error is caused by an update conflict, then the update conflict handler is invoked. If the update conflict handler resolves the conflict successfully, then the apply process continues applying the other LCRs in the transaction that should be applied according to the apply process rule sets. In this case, the error handler is not invoked.

If the update conflict handler cannot resolve the conflict, then the error handler is invoked. If the error handler does not raise an exception, then the apply process assumes the error handler has performed the appropriate action with the row LCR, and the apply process continues applying the other LCRs in the transaction that should be applied according to the apply process rule sets. If the error handler cannot process the LCR, then the error handler should raise an exception. In this case, the transaction containing the row LCR is rolled back, and all of the LCRs in the transaction that should be applied according to the apply process rule sets are moved to the error queue.

Apply and Streams Replication

Nel documento Oracle® Streams Replication Administrator’s Guide 10g (pagine 39-42)