create Primary constraint using existing unique index took 9 hours

The table and indexes were just created using impdp, took 6 hours in heavily loaded system.

The unique index used by this constraint took about 20 minutes to create.

The problem is occurring with this one primary constraint.

Other primary constraints using existing unique index took only seconds, even on large tables and indexes.

No blocking lock were observed.

An earlier execution, running about stand alone, took 3.5 hours.

01:38:58 SQL>
01:38:58 SQL> ALTER TABLE "XXXX"."PSTNG_LN_CAT"
01:38:58   2  ADD CONSTRAINT "PK_PSTNGLNCAT_PSTNG_LN_CATDOC"
01:38:58   3  PRIMARY KEY ("DOC_CD", "DOC_DEPT_CD", "DOC_ID", "DOC_VERS_NO", "DOC_PSTNG_NO")
01:38:58   4  ENABLE;

Table altered.

Elapsed: 08:56:51.84