private void checkAcidConstraints() {
    /*
    LOG.info("Modifying config values for ACID write");
    conf.setBoolVar(ConfVars.HIVE_OPT_REDUCE_DEDUPLICATION, true);
    conf.setIntVar(ConfVars.HIVE_OPT_REDUCE_DEDUPLICATION_MIN_REDUCER, 1);
    These props are now enabled elsewhere (see commit diffs).  It would be better instead to throw
    if they are not set.  For exmaple, if user has set hive.optimize.reducededuplication=false for
    some reason, we'll run a query contrary to what they wanted...  But throwing now would be
    backwards incompatible.
    */
    conf.set(AcidUtils.CONF_ACID_KEY, "true");
    SessionState.get().getConf().set(AcidUtils.CONF_ACID_KEY, "true");
  }
Merge stmt with early split update may create several (2) writes to the same
table with the same {@link WriteType}, e.g. if original Merge stmt has both update and
delete clauses, and update is split into insert + delete, in which case it's not an
error
ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java