EXPLAIN、STATIC EXPLAIN、DYNAMIC EXPLAINリクエスト修飾子を使用すると、テンポラル セマンティクスの操作についてのレポートが得られます。この説明文には、操作対象のテンポラル テーブルに適用された修飾子のタイプが示されます。この修飾子は、問合わせがcurrent、sequenced、またはnonsequencedのどれになるのかをレポートします。
ここでは、行パーティション二重テンポラル テーブルに対するcurrent問合わせについてのEXPLAINレポートの例を示します。
EXPLAIN SELECT * FROM Policy;
Explanation
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1) First, we lock DBASE.Policy for read on a reserved RowHash
in all partitions to prevent global deadlock for DBASE.Policy.
2) Next, we lock DBASE.Policy for read.
3) We do an all-AMPs RETRIEVE step from a single partition of
DBASE.Policy (with temporal qualifier as "CURRENT
VALIDTIME AND CURRENT TRANSACTIONTIME") with a condition of (
"((BEGIN(DBASE.Policy.Validity ))<= DATE '2010-02-18')
AND (((END(DBASE.Policy.Policy_Duration ))= TIMESTAMP
'9999-12-31 23:59:59.999999+00:00') AND
((END(DBASE.Policy.Validity ))> DATE '2010-02-18'))")
into Spool 1 (group_amps), which is built locally on the AMPs.
The size of Spool 1 is estimated with no confidence to be 1 row (
85 bytes). The estimated time for this step is 0.03 seconds.
4) Finally, we send out an END TRANSACTION step to all AMPs involved
in processing the request.
-> The contents of Spool 1 are sent back to the user as the result of
statement 1. The total estimated time is 0.03 seconds.