Oracle stream - Downstream

Question

I am getting the below error now on downstream database. This constraint doesn't exist on downstream because I am
excluding constraint on downstream
when importing.
ORA-00001: unique constraint (PCAT_NT.PK01_DCS_CAT_CATINFO) violated
Is this mandatory to include constraint in Oracle stream setup?
My steps are as below:
1) Create the downstream capture process
BEGIN
DBMS_CAPTURE_ADM.CREATE_CAPTURE (
queue_name => 'STRMPCAT_QUEUE',
capture_name => 'DOWNSTRMPCAT_CAPTURE',
rule_set_name => null,
start_scn => null,
source_database => 'PCAT',
use_database_link => true,
first_scn => null,
logfile_assignment => 'IMPLICIT');
END;
2) Add schema rule on Downstream database
BEGIN
DBMS_STREAMS_ADM.ADD_SCHEMA_RULES(
schema_name => 'PCAT_NT',
streams_type => 'CAPTURE',
streams_name => 'DOWNSTRMPCAT_CAPTURE',
queue_name => 'STRMPCAT.STRMPCAT_QUEUE',
include_dml => true,
include_ddl => false,
source_database => 'PCAT');
END;
3) Initializing SCN on Downstream database
--on source
expdp system SCHEMAS=PCAT_NT DIRECTORY=DATA_PUMP_DIR DUMPFILE=PCAT_expdp.dmp exclude=user,grant,statistics,synonyms,procedure,constraint FLASHBACK_SCN=7620529799615
--on target
impdp system SCHEMAS=PCAT_NT DIRECTORY=DATA_PUMP_DIR DUMPFILE=PCAT_expdp.dmp
Regards

Answer 1

Are you stating that the constraint PCAT_NT.PK01_DCS_CAT_CATINFO does not exist on the destination database and that you are getting a constraint violation error on the destination database? That strikes me as exceptionally unlikely.
How do you know that the constraint was not created on the destination database? I would tend to suspect that you created the constraint potentially unintentionally.
I would be interested in why you're getting duplicate rows as well. If there are no duplicate rows in the source database, duplicates in the destination would imply that you're doing something wrong in the setup (i.e. the SCN in your export is incorrect) or that you have something in the Streams config which is causing duplicates (i.e. a custom DML handler).
Justin