17.00 - 17.05 - 結合を最適化しない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ないと、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:マージ結合 コピーoptions、直接size 0.46
Spool 4:プロダクト ジョイン コピーcolor、直接widgets 12 491.00

これは、3時間28分11秒と同等です。

Spool 1:マージ結合 コピー3、ローカル4 21.05

完了時間

実行時間の見積もりの合計は、3時間28分です。

最適化しない結合計画のEXPLAIN出力

LT/ST最適化なしで生成されたEXPLAIN出力の一部を次に示します。

2) Next, we execute the following steps in parallel.
   a) 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 6
      rows. The estimated time for this step is 0.11 seconds.
   b) 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.Widgets.description =
      TEST.Options.description“). 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 20 rows. The
      estimated time for this step is 0.46 seconds.
3) We do an all-AMPs JOIN step from Spool 2 (Last Use) by way of an
   all-rows scan, which is joined to TEST.Widgets. Spool 2 and
   TEST.Widgets are joined using a product join, with a join condition
   of (“TEST.Widgets.color = Spool_2.code”). The result goes 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
   500,000 rows. The estimated time for this step is 3 hours and 28
   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.options = Spool_3.code) AND (Spool_4.size =
   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 555
   rows. The estimated time for this step is 21.05 seconds.