The role of Oracle analyze table __oracle

Let's take a brief note.

Today, helping colleagues guide the data, from the development environment to the test environment, found that a query is slow. See the execution plan, and found that the full table scan (about 300w records in the table), why not use the index, view the index status, everything is normal. Dizzy.
Must be the index of the problem, first analysis of the table to say.
Analyze table Ysgl_compile_reqsub Compute statistics for all indexes;

It's normal.

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A post on the forum:

Oracle performance improvement with Analyze table
Url:http://www.itpub.net/thread-295293-1-1.html

Let's talk about this optimization project.
One of the real facts I've come across:
One SQL statement execution takes 1 hours, and sometimes results are not, but after analyzing the tables involved in SQL, then perform 3 minutes to get it done again.
There really is such an amazing difference.

There is no absolute, sometimes you may find that it slows down
Knowing the CBO and Rbo, you know the difference.

The Annlyze table increases the performance of CBO execution. No, not necessarily.
I just ran into a statement. The analysis is performed for more than 30 minutes, after which the analysis is deleted for only 30 seconds.
In many cases, it's best to judge yourself from the execution plan.

This is another way to understand the Oracle optimizer = = Whether I can start to read page 25th.