Oracle SQL parsing flow digoal (SQL parsing flowchart)

Here is a document about the SQL parsing flowchart on MOS. For details, refer to [id32895.1]. The main part of the screenshot is as follows:

Thisarticle show the parsing mechanism as a flow digoal. its main purpose is toshow the difference between a 'soft' and a 'hard' parse. it is intended to givea feel of how parsing operates to make explanation of parsing activity easier.

 

 

 

 

Note:

1. A cursor is an address on the client that points tothe memory location of a SQL statement on the server. Multiple-client cursors may point at the same address on the server.

 

2. Remember that 'client' and 'server' sides may reside on the same machine-in which caseclient/Server is a logical distinction.

 

3. if a cursor is open, then thestatement will be in the SQL _area, so no Parsing is necessary. this iswhy locks may remain when a client is terminated abnormally (such as a pcclient being turned off without closing open cursors ).

 

4. session_cached_cursors is the initialisation parameterthat specifies how many cursors to hold open for a special session. the opencursor request will still be sent to the server but it will not be executedonce a matching cursor is found in the session cursor cache.

 

5. hold_cursor is an precompiler parameter that specifiesthat an individual cursor shoshould be held open.

 

6. Both the soft and hard parseregister as a parse in tkprof. hashing the current statement updates theparse count.

 

 

7. soft parse avoids expiration of thesteps taken during the parse phase for a particle statement. initialsyntactic and semantic checks are made and then the statement is hashed andcompared with hashed statements in the SQL area. if amatch is found, then existing information is used and relatively expensivesteps (such as query optimization etc .) areavoided.

 

8. The 10053 event is only invoked during a hard parse.

 

Oracle 10053 events

Http://blog.csdn.net/tianlesoftware/article/details/5859027

 

 

 

 

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