17.00 - 17.05 - スター結合最適化とファクト テーブルUSIを使用する合理的なインデックス結合計画 - 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)

結合を最適化した場合には、大さなテーブルの固有セカンダリ インデックスが結合列の集まり(color、size、およびoptions)で構成されていると、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 3: プロダクト ジョイン コピーcolor、直接options 0.31
Spool 5: プロダクト ジョイン コピーsize、直接3 1.62
Spool 6:入れ子結合 ハッシュ5、インデックスwidgets 2.71
Spool 1:行ID結合 ハッシュ6、インデックスwidgets 5.65

完了時間

実行時間の見積もりの合計は、10.07 秒です。

性能向上係数の見積もりは、667です。

最適化する結合計画のEXPLAIN出力

この最適化された結合計画のEXPLAIN出力の一部を次に示します。

2) Next, we do an all-AMPs RETRIEVE step from TEST.Color by way of an
   all-rows scan with no residual conditions into Spool 2, which is
   duplicated on all AMPs. The size of Spool 2 is estimated to be 4
   rows. The estimated time for this step is 0.08 seconds.
3) We execute the following steps in parallel.
   a) We do an all-AMPs JOIN step from Spool 2 (Last Use) by way of an
      all-rows scan, which is joined to TEST.Options. Spool 2 and
      TEST.Options are joined using a product join. The result goes
      into Spool 3, which is built locally on the AMPs. The size of
      Spool 3 is estimated to be 20 rows. The estimated time for this
      step is 0.23 seconds.
   b) We do an all-AMPs RETRIEVE step from TEST.Size by way of an
      all-rows scan with no residual conditions into Spool 4, which is
      duplicated on all AMPs. The size of Spool 4 is estimated to be 20
      rows. The estimated time for this step is 0.24 seconds.
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 product join. The result goes into Spool
   5, which is redistributed by hash code to all AMPs. Then we do a
   SORT to order Spool 5 by row hash. The size of Spool 5 is estimated
   to be 200 rows. The estimated time for this step is 1.38 seconds.
5) We do a all-AMP JOIN step from Spool 5 (Last Use) by way of an
   all-rows scan, which is joined to TEST.Widgets by way of unique
   index # 4 extracting row ids only. Spool 5 and TEST.Widgets are
   joined using a nested join. The result goes into Spool 6, which is
   redistributed by hash code to all AMPs. Then we do a SORT to order
   Spool 6 by row hash. The size of Spool 6 is estimated to be 200
   rows. The estimated time for this step is 2.71 seconds.
6) We do an all-AMPs JOIN step from Spool 6 (Last Use) by way of an
   all-rows scan, which is joined to TEST.Widgets. Spool 6 and
   TEST.Widgets are joined using a row id join. The result goes into
   Spool 1, which is built locally on the AMPs. The size of Spool 1 is
   estimated to be 200 rows. The estimated time for this step is 5.65
   seconds.