SQLT(SQLTXPLAIN)

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SQLT也叫SQLTXPLAIN，如果某一条SQL执行效率很低，也不知道从哪里下手，可以使用SQLT来收集和性能相关的各种信息(如:Execution plans, Cost-based Optimizer CBO statistics, Schema objects metadata, Performance statistics, Configuration parameters...)

一般情况下SQLT的output可以回答很多问题，比如：
How many and which tables are involved?
How big are the objects involved?
How many, what type and what columns are indexed?
How accurate are the optimizer statistics?
Are there histograms on the columns?
Are there any non-default init.ora parameters that could be causing problems?
What is the execution plan?
Has it changed recently?
......

详见Note 215187.1 : SQLT (SQLTXPLAIN) - Tool that helps to diagnose SQL statements performing poorly
Step 1) Download SQLT
Step 2) Install SQLT
Step 3) Execute SQLT

Step 4) Review the output