ORA-23402: refresh was aborted because of

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ORA-23402: refresh was aborted because of conflicts caused by deferredtxns
Cause: There are outstandingconflicts logged in the DefError table at the
materialized view's master.
Action: Resolve the conflictsin the master DefError table and refresh again after
the table is empty. Alternatively, refresh with refresh_after_errors set toTRUE,
which will proceed with the refresh even if there are conflicts in the master's
DefError table. Proceeding despite conflicts can result with an updatable
materialized view's changes appearing to be temporarily lost (until a refresh
succeeds after the conflicts are resolved).