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SQL Parsing Flow Diagram

原创 Linux操作系统 作者:浪漫双鱼 时间:2011-07-30 22:41:44 0 删除 编辑
SQL Parsing Flow Diagram
========================
 
 Statement 
 Submitted
 |
 Is it in an open cursor?--------------YES----V   
 |                                            |  
 NO                                           |   
 |                                            |
 Is SESSION_CACHED_CURSORS = Value            |  
 and cursor in Server Side ------------YES----V   In these 3 cases we  
 Session Cursor cache?                        |   know that the cursor has 
 |                                            |   already been parsed, so 
 NO                                           |   re-parsing is
 |                                            |   unnecessary.
 Is HOLD_CURSOR=Y                             |
 and cursor in           --------------YES----V      
 Held cursor cache?                           |       
 |                                            |       
 NO                                           |        
 |                                            |              ^
 OPEN A CURSOR                                |  CLIENT SIDE |       
 |                                            | -------------|
 Statement is Hashed and compared             |  SERVER SIDE | 
 with the Hashed value in the sql area        |              V
 |                                            V
 Is it in sql area? --YES-(Soft Parse)--> ---------
 |                                       |         |
 NO                                      | EXECUTE |
 |                                       |         |
 PARSE STATEMENT ('Hard' Parse)---------> ---------

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