How Tags are used in Streams

The tag value for the current session can be displayed by querying the dual view:

SELECT DBMS_STREAMS.GET_TAG FROM DUAL
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Since an Apply process is typically an SQL session that makes the transactional changes on the destination database, it does generate the redo entries. Such redo entries will have Non-NULL tags in order to avoid further capture. By default, the non-NULL value is system dependent. However, if the goal is to create a specific non-NULL tag value, the alter_apply procedure of the dbms_apply_adm procedure can be used to set up desired non-NULL tag value.

In another situation, the default tag for all redo entries generated by an Apply process can also be set when the Apply process is created. In this case, the create_apply procedure in the dbms_apply_adm package will be used.

For example, to set the value of the tags generated in the redo log by an existing apply process named nydata1_apply to the hexadecimal value of 6, run the following SQL block:

BEGIN
DBMS_APPLY_ADM.ALTER_APPLY(
apply_name => 'nydata1_apply', apply_tag => HEXTORAW(‘6’));
END;
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