Oracle GoldenGate When Table column is generate always identity type_IT does not let insert in target DB table

Trying to replicate the data into the replica DB (target) from source DB, using Oracle Golden Gate (OGG). Let's say I have TableA and B in source DB. A has identity column managed by a trigger which add unique number using sequence object (the old Oracle way, prior to 12C). The table B has identity column as "GENERATE ALWAYS AS IDENTITY ...", the way came newly in 12C. Now below is my observation, followed by question: (A) SourceDB TableA, insert 1 record, id=1. Then in TargetDB TableA, OGG replicates 1 insert, id=1. Good.

Source A------------------------------------Target A
id=1----------------------------------------id=1

(B) In TargetDB, manually insert 1 record, it gets done, id=3. Good. Here id should have been 2 but OGG skips 2 and set id of this newly added record in Target table as 3.

Source A------------------------------------Target A
id=1----------------------------------------id=1
.-------------------------------------------id=3

(C) SourceDB TableA, insert 1 record, id=2. Then in TargetDB TableA, OGG replicates 1 insert, id=2. Good.

Source A------------------------------------Target A
id=1----------------------------------------id=1
.-------------------------------------------id=3
id=2----------------------------------------id=2

So, apart from the nice behavior of the OGG it looks good! But when the same thing I try to do on the TableB, it gives me unique constraint error in Step B!! It looks like because the Table B the identity column is defined as Generate Always as Identity. So, it is really because of this? And this new way cause more problem then the old way of using sequence.nextValue object to generate new unique id column. Or there is any way in OGG to overcome this and make this table B behave same as Table A, for the step B?

Let's split your question in the two scenarios:

SEQUENCES

For a sequence, you can ONLY replicate in one-way replications. This means You can't replicate a sequence in an two-way or multi-way replication. You can ONLY replicate in an active-passive HA (high availability) not an active-active HA setup. You need to turn off the sequence replication by:

• Excluding sequence capture from the capture (extract) using TABLEEXCLUDE.
• Disabling triggers that process sequences with DBOPTIONS SUPRESSTRIGGERS in the delivery (REPLICAT).

During a replication, Oracle GoldenGate captures the sequence updates and makes sure the target sequence value is equal or higher than the source sequence number:

• If the NOCACHE option is specified in the sequence, an data entry will show in the GoldenGate trail every time the sequence is updated.
• If the CACHE option is specified for the sequence, an data entry will show in the GoldenGate trail every time the high water mark is updated.

IDENTITY COLUMNS

Capture and replication of identity columns are supported by integrated processes from OGG v18 onwards.

• Capture and replication supported by integrated extracts and replicates only. All other nonintegrated modes do not support identity column replication, including classic parallel and coordinated replicates.
• Only RDBMS 18.x and above with OGG v18 and above supports replication for identity columns.
• Allows for bidirectional replication of identity columns from OGG v18 and above
• If the target column is an identity column, OGG replicate will overwrite the target using the value from the source.
• There are no restrictions on how the IDENTITY property is set on the source or the target
• This feature cannot be backported to older versions.
• An empty table has an identity column added to it by ALTER TABLE ADD is still not supported.