private void overrideTblProps(JobConf job, Map<String, String> tblproperties, String properties) {
    StringableMap stringableMap = new StringableMap(properties);
    overrideMRProps(job, stringableMap);
    // mingle existing tblproperties with those specified on the ALTER TABLE command
    for (String key : stringableMap.keySet()) {
      if (key.startsWith(TBLPROPS_PREFIX)) {
        String propKey = key.substring(9);  // 9 is the length of "tblprops.". We only keep the rest
        tblproperties.put(propKey, stringableMap.get(key));
      }
    }
    // re-set TABLE_PROPS with reloaded tblproperties
    job.set(TABLE_PROPS, new StringableMap(tblproperties).toString());
  }
Parse tblproperties specified on "ALTER TABLE ... COMPACT ... WITH OVERWRITE TBLPROPERTIES ..."
and override two categories of properties:
1. properties of the compactor MR job (with prefix "compactor.")
2. general hive properties (with prefix "tblprops.")
@param job the compactor MR job
@param tblproperties existing tblproperties
@param properties table properties
ql/src/java/org/apache/hadoop/hive/ql/txn/compactor/MRCompactor.java