UPDATE操作の実行時に結合インデックスを保守するための一般的な方法 - Advanced SQL Engine - Teradata Database

UPDATE操作の実行時に結合インデックスを保守するための一般的な方法の例

EXPLAIN出力では、次の項目に注意してください。

     EXPLAIN
     UPDATE lineitem
     SET l_extendedprice=l_extendedprice * .80
     WHERE l_partkey=50;

EXPLAIN出力の一部を次に示します。

  4) We do an all-AMPs RETRIEVE step in TD_MAP1 from DB1.ORDERJOINLINE
     by way of an all-rows scan with a condition of (
     "DB1.ORDERJOINLINE.l_partkey = 50") into Spool 1 (all_amps),
     which is built locally on the AMPs.  The size of Spool 1 is
     estimated with no confidence to be 1 row (53 bytes).  The
     estimated time for this step is 0.15 seconds.
  5) We do an all-AMPs RETRIEVE step in TD_Map1 from Spool 1 by way of
     an all-rows scan into Spool 2 (all_amps), which is redistributed
     by the hash code of (DB1.ORDERJOINLINE.l_orderkey) to all AMPs in
     TD_Map1.  Then we do a SORT to order Spool 2 by row hash.  The
     size of Spool 2 is estimated with no confidence to be 1 row (53
     bytes).  The estimated time for this step is 0.07 seconds.
  6) We execute the following steps in parallel.
       1) We do an all-AMPs MERGE DELETE to DB1.ORDERJOINLINE from
          Spool 2 (Last Use).  The size is estimated with no confidence
          to be 1 row.  The estimated time for this step is 4.60
          seconds.
       2) We do an all-AMPs RETRIEVE step in TD_Map1 from Spool 1 (Last
          Use) by way of an all-rows scan into Spool 3 (all_amps),
          which is redistributed by the hash code of (
          DB1.ORDERJOINLINE.l_orderkey) to all AMPs in TD_Map1.  Then
          we do a SORT to order Spool 3 by join index.  The size of
          Spool 3 is estimated with no confidence to be 1 row (53
          bytes).  The estimated time for this step is 0.16 seconds.
  7) We execute the following steps in parallel.
       1) We do an all-AMPs MERGE step in TD_MAP1 into
          DB1.ORDERJOINLINE from Spool 3 (Last Use).  The size is
          estimated with no confidence to be 1 row.  The estimated time
          for this step is 1.34 seconds.
       2) We do an all-AMPs UPDATE step in TD_MAP1 from DB1.lineitem
          by way of an all-rows scan with a condition of (
          "DB1.lineitem.l_partkey = 50").  The size is estimated with
          no confidence to be 2 rows.  The estimated time for this step
          is 0.10 seconds.
  8) We spoil the parser's dictionary cache for the table.
  9) Finally, we send out an END TRANSACTION step to all AMPs involved
     in processing the request.
  -> No rows are returned to the user as the result of statement 1.