17.00 - 17.05 - 結合を最適化する合理的な非インデックス結合 - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - SQLリクエストおよびトランザクション処理

Product
Advanced SQL Engine
Teradata Database
Release Number
17.00
17.05
Published
2020年6月
Content Type
プログラミング リファレンス
ユーザー ガイド
Publication ID
B035-1142-170K-JPN
Language
日本語 (日本)

スター結合の最適化が適用されると、次の結合計画が生成されます。

操作 結合テーブル 処理時間合計(秒)
Spool 2:マージ結合 コピーoptions、直接size 0.44
Spool 3:プロダクト ジョイン 直接color、コピー2 1.24
Spool 1:マージ結合 ローカルwidgets、コピー3 7,761.00

これは、2時間9分21秒と同等です。

完了時間

実行時間の見積もりの合計は、2時間9分です。

性能向上係数の見積もりは、1.6です。

最適化する結合計画のEXPLAIN出力

生成されたEXPLAIN出力の一部を次に示します。

2) Next, we do an all-AMPs JOIN step from TEST.Options by way of an
   all-rows scan with no residual conditions, which is joined to
   TEST.Size. TEST.Options and TEST.Size are joined using a merge join,
   with a join condition of (“TEST.Size.description =
   TEST.Options.description“). The result goes into Spool 2, which is
   duplicated on all AMPs. The size of Spool 2 is estimated to be 20
   rows. The estimated time for this step is 0.44 seconds.
3) We execute the following steps in parallel.
   a) We do an all-AMPs JOIN step from TEST.Color by way of an
      all-rows scan with no residual conditions, which is joined to
      Spool 2 (Last Use). TEST.Color and Spool 2 are joined using a
      product join. The result goes into Spool 3, which is duplicated
      on all AMPs. Then we do a SORT to order Spool 3 by row hash. The
      size of Spool 3 is estimated to be 60 rows. The estimated time 
      for this step is 1.24 seconds.
   b) We do an all-AMPs RETRIEVE step from TEST.Widgets by way of an
      all-rows scan with no residual conditions into Spool 4, which is
      built locally on the AMPs. Then we do a SORT to order Spool 4 by
      row hash. The size of Spool 4 is estimated to be 1,000,000 rows.
      The estimated time for this step is 2 hours and 9 minutes.
4) We do an all-AMPs JOIN step from Spool 3 (Last Use) by way of an
   all-rows scan, which is joined to Spool 4 (Last Use). Spool 3 and
   Spool 4 are joined using a merge join, with a join condition of (
   “(Spool_4.color = Spool_3.code) AND ((Spool_4.size = Spool_3.code
   AND (Spool_4.options = Spool_3.code ))“). The result goes into Spool
   1, which is built locally on the AMPs. The size of Spool 1 is
   estimated to be 556 rows. The estimated time for this step is 21.94
   seconds.