Nigel是Oracle Optimizer的产品经理。他从1988年开始做与Oracle技术相关的工作，1996年加入甲骨文公司。他参与了各种各样的工作，包括开发、基准测试、咨询和售前工作。下面的内容来自他在oracle blog的内容。原文地址：https://blogs.oracle.com/optimizer/whats-new-in-the-oracle-optimizer-for-oracle-database-19c
For those of you that want to keep up-to-speed with the latest changes, this post includes a quick summary of the headline new features in Oracle Database 19c with links to the documentation. In addition, most of the new optimizer white papers have been published. You will find links to them in the new Oracle Query Optimization page (and there will be further updates to this page soon).
This is a complex and sophisticated piece of functionality but, ironically, it requires only a tiny API because it has been designed to be very easy to use and require virtually zero manual intervention. I'm sure that you can expect a lot to be written about this feature, but you can find material in the SQL Tuning Guide and the DBMS_AUTO_INDEX API.
Statistics can now be collected 'on-the-fly' during conventional DML operations. This feature requires no manual intervention, but you can find details in the SQL Tuning Guide's Optimizer Statistics Concepts chapter.
High-Frequency Statistics Gathering
Real-time statistics are a complement to conventional gathered statistics, so there is still a need for both. To help keep gathered statistics up-to-date, we added a new task to do it more frequently. It is again documented in the SQL Tuning Guide.
Automatic SQL Plan Management
There is a lot to say about this feature, so my intention is to post a blog in the next few of weeks. We have included more automation in the SQL evolve advisor task, so see the new features guide and the section on managing SQL plan baselines.
Documentation for the SQL plan management (SPM) API can be found in the DBMS_SPM API section. Note that the following SQL plan management task parameters have new default values in Oracle Database 19c:
PARAMETER_NAME DEFAULT -------------------------------- ---------- ALTERNATE_PLAN_BASELINE AUTO ALTERNATE_PLAN_LIMIT UNLIMITED ALTERNATE_PLAN_SOURCE AUTO
If you currently use SQL plan management, especially if you use it to micro-manage individual SQL execution plans, then you need to be aware of the new default behavior when upgrading to Oracle Database 19c. You do have a choice: you can use the new defaults immediately or, if you prefer, you can set these parameters back to the pre-19c defaults very easily.
An additional piece of SQL plan management functionality was added late-in-the-day, so that will make its way through soon. I will post an update here when it's documented.
Hint Usage Reporting
Diagnosing SQL statement hint issues can be difficult. More information on how we have made is easier can be found in the documentation and in this blog post. Using this feature to diagnose issues with SQL plan baselines is presented in this blog post.
SQL Plan Comparison
We've made it much easier to compare a 'reference' SQL execution plan with multiple plans from a variety of different sources using a single API call. It's a great tool for diagnosis and you can find details in the section on comparing execution plans in the documentation. The API is DBMS_XPLAN.COMPARE_PLANS.
This feature allows you to prevent runaway SQL statements from consuming all your system resource. It is covered in detail in the Database Administrator's Guide chapter on Diagnosing and Resolving Problems.
Automatic Diagnosis and Repair
The process of diagnosing and repairing problems has been enhanced to make it easier to treat issues with the DBMS_SQLDIAG API and the addition of the V$SQL_TESTCASES view.
There's more in in the Database Administrator's Guide.
Not all of these features will be available on all database platforms. Consult the Database Licensing Information User Manual for details