LOOP PREVENTION

From version 2.8 onwards Replicate parameters APPLY_LOOP_PREVENTION and MINE_LOOP_PREVENTION will become public ones.

This page is trying to shed some light onto the meaning of the APPLY_LOOP_PREVENTION and MINE_LOOP_PREVENTION parameters.

Replicate does filtering of transactions based on TRANSACTION_NAME which contains "DBREPL_database_name_XID". 

APPLY_LOOP_PREVENTION ( YES on default)

Purpose:  

•  Changes that are mined on the source server and then applied on the target server are not mined again on the target server. This is prevented by the APPLY_LOOP_PREVENTION setting.
• Based on TRANSACTION_NAME the APPLY_LOOP_PREVENTION throws transaction out on APPLY - if the database name matches current database meaning it just completed a loop.
• It also checks if the DDL was done by an apply process on this db; modify the DDL by adding comment to the end so next mine/apply can check that it was done by apply.

Valid Settings: YES or NO

MINE_LOOP_PREVENTION ( NO on default)

Purpose:  

• Changes that are mined on the source server and then applied on the target server. This is controlled by the MINE_LOOP_PREVENTION setting.
• MINE_LOOP_PREVENTION throws out transaction based on the TRANSACTION_NAME that contains "DBREPL_database_name_XID". 

                 If set to YES it checks if Replicate does skip this DDL due to: 

• • it is created by an APPLY process and APPLY adds a comment to end of the DDL.

This is disabled - Replicate need to pass at least CREATE TABLE to APPLY; it just lets APPLY_LOOP_PREVENTION do it's job for DDL

• • an established isolation level triggered by a SET TRANSACTION statement

Comment: MINE_LOOP_PREVENTION is preferred to APPLY_LOOP_PREVENTION as the changes are filtered sooner and don't even get written to a PLOG file. But it's too aggressive in more complicated scenarios.

Valid Settings: YES or NO

Filtering deletes at a transaction level

Filter the data to be replicated