Oracle Database 19c Release Update 19.7公开了一个新的数据库基础结构组件，称为自动SQL调优集（ASTS）。在本次发布更新（RU）中，它默认处于启用状态，但Oracle已决定在此数据库版本的未来RU中默认禁用它，决定启用它的责任在用户。 因此，在Oracle Database 19c Release Update 19.8中，默认情况下是禁用的。
如果你想了解更多有关它是什么，它的目标，如何控制它以及它使用了多少系统资源等，请查阅MOS中有关该主题的文章：《Automatic SQL Tuning Sets (ASTS) 19c RU 19.7 Onwards (Doc ID 2686869.1)》
简而言之，它是一个系统维护的SQL调优集，是历史SQL性能指标和执行计划的非常有用的来源。您可以使用SQL plan management快速修复SQL性能退化(点此链接查看具体方法)。我知道有些客户担心它有时会捕获大量的SQL语句，并会停顿一下。它是被设计成这样工作的。如果你关心这些，是很容易检查它使用的资源量（MOS文章中有详细信息）的。例如，将ASTS在SYSAUX的使用量与AWR做比较。所以，给它一个机会，你可能会发现它是Oracle数据库工具包中最有用的工具之一。
原文链接 ： https://blogs.oracle.com/optimizer/post/what-is-the-automatic-sql-tuning-set
What is the Automatic SQL Tuning Set?
July 22, 2020 | 1 minute read
Nigel Bayliss
Product Manager
Oracle Database 19c Release Update 19.7 exposed a new database infrastructure component called the automatic SQL Tuning Set (ASTS). It was on by default in this Release Update (RU) but Oracle has decided to disable it by default in future RUs for this database release, giving customers the responsibility to enable it explicitly. It is therefore disabled by default in Oracle Database 19c, Release Update 19.8.
If you want to know more about what it is, its purpose, how to control it and also see how much system resources it uses, then take a look at the MOS note on the topic:
Automatic SQL Tuning Sets (ASTS) 19c RU 19.7 Onwards (Doc ID 2686869.1)
In short, it is a system-maintained SQL tuning set that is an incredibly useful source of historic SQL performance metrics and execution plans. You can use it to repair SQL performance regressions very quickly using SQL plan management. I know that some customers are worried that it sometimes captures a very large number of SQL statements, but pause for a moment. It is designed to work like this, and the amount of resource it uses is very easy to check if you are concerned about it (the MOS note has details). Compare ASTS usage of SYSAUX with AWR, for example. So give it a chance - and you might find that it’s one of the most useful tools the Oracle Database has in its toolkit.
