Talk about SQL profile again: can I fix the execution plan?

After I released the use of coe_load_sql_profile.sql The script can solve the problem that the execution plan of the production system suddenly deteriorates , I happened to see another article the next day ：《 Implementation plan ：Oracle Of Profile Characteristics and SQL Stability of execution plan 》, The article is dedicated to sql profile Made an in-depth introduction , To understand SQL profile The principle of is very helpful . Because both the writer and the forwarder are big winners in the industry , Many fans , Many people should have read that article , Therefore, it is necessary to correct a minor flaw in the article , namely “SQL profile The execution plan cannot be fixed ” This conclusion is not accurate , Just a result under certain test conditions .

The following figure is the conclusion of the article ：

Used by the author of the article Test case in , It should be possible to get such a result , But the conclusion is not complete , Will give the reader a misleading ：SQL prfofile The execution plan cannot be fixed .

The above conclusion is that oracle Of sql tuning advisor Tool generated sql profile（ Write only one opt_estimate One of them is hint）, As an optimization tool , For such a SQL It is understandable not to be completely fixed . This also reminds us of DBA, use sql tuning advisor It's done sql profile It may not be able to execute the plan regularly .

I would like to add that ： If in sql profile The complete outline data, The plan can be executed in a fixed way , For example, the following one SQL complete Hint Write the contents of profile：

/*+

BEGIN_OUTLINE_DATA

IGNORE_OPTIM_EMBEDDED_HINTS

OPTIMIZER_FEATURES_ENABLE('11.2.0.3')

DB_VERSION('11.2.0.3')

ALL_ROWS

OUTLINE_LEAF(@"SEL$1")

FULL(@"SEL

INDEX(@"SEL

LEADING(@"SEL

USE_NL(@"SEL

NLJ_BATCHING(@"SEL

END_OUTLINE_DATA

*/

This profile Yes you can specify SQL Which index to use , The association mode and order of tables .

Conclusion ：

sql profile Can it be fixed sql Implementation plan of ？

The answer depends on where you are profile Used in hint What is the combination . Use the complete outline data The content can be fixed ; Use incomplete , Enlightening hint, Will not be fixed .

Use coe_sql_load_profile.sql The script will fix your SQL Implementation plan of （ Because it writes profile One of the contents of sql complete outline data Execution plan execution path ）, Unless there's something special , If the index is not available 、 Insufficient parallel resources 、 Database related parameter changes, etc .