protected void initTasks(){
    tasks = ImmutableMap.<FailableRunnable<MetaException>, String>builder()
            .put(txnHandler::performTimeOuts, "Cleaning timed out txns and locks")
            .put(txnHandler::performWriteSetGC, "Cleaning obsolete write set entries")
            .put(txnHandler::cleanTxnToWriteIdTable, "Cleaning obsolete TXN_TO_WRITE_ID 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/AcidHouseKeeperService.java