@Override
  protected void initTasks(){
    tasks = ImmutableMap.<FailableRunnable<MetaException>, String>builder()
            .put(txnHandler::removeDuplicateCompletedTxnComponents,
                    "Cleaning duplicate COMPLETED_TXN_COMPONENTS entries")
            .put(txnHandler::purgeCompactionHistory, "Cleaning obsolete compaction history entries")
            .build();
  }
Performs background tasks for Transaction management in Hive.
Runs inside Hive Metastore Service.
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/txn/service/CompactionHouseKeeperService.java