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.