Oracle architecture and backup (2) Analysis of the select statement execution process

One environment, two operation examples Microsoft Windows [Version6.1.7601] Copyright (c) 2009MicrosoftCorporation. Allrightsreserved. C: UsersWentasysqlplusscottSQL * Plus: Release11.2.0.1.0Produ

One environment Oracle 11g R2 SQL Plus Windows 7 Ultimate English Edition two operation examples Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. all rights reserved. c: \ Users \ Wentasysqlplus scottSQL * Plus: Release 11.2.0.1.0 Produ

I. Environment

Oracle 11g R2 + SQL Plus + Windows 7 Ultimate English Edition

Example 2

Microsoft Windows [Version 6.1.7601] Copyright (c) 2009 Microsoft Corporation. all rights reserved. c: \ Users \ Wentasy> sqlplus scottSQL * Plus: Release 11.2.0.1.0 Production on Tuesday May 28 15:17:49 2013 Copyright (c) 1982,201 0, Oracle. all rights reserved. enter the password: connect to: Oracle Database 11g Enterprise Edition Release 11.2.0.1.0-ProductionWith the Partitioning, OLAP, Data Mining and Real Application Testing optionsSQL> SELECT * FROM emp WHERE empno = 7839; empno ename job mgr hiredate sal comm ---------- --------- ---------- -------------- ---------- DEPTNO ---------- 7839 king president 17-11 month-81 5000 10

3. Analysis

1. the user process executes a statement, such as select * from emp where empno = 7839;

2. the user process has established a connection with the server process and stored the user process information in the UGA of PGA.

3. The statement is passed to the instance after being processed by PGA.

4. The shared pool in the instance is responsible for processing this statement. Sharing pool processing: First, you can determine how statements are analyzed, soft analysis, or hard Analysis in the database cache area. If it is soft analysis, the execution will be fast, and the hard analysis will go through many steps. Both soft analysis and hard analysis are prepared to execute the statement according to the execution plan obtained by the CBD.

5. query the tablespace in which the objects are stored and the specified row is placed in the block.

6. The data dictionary cache area obtains the information.

7. Start execution. Determine whether the required block is cached in the data buffer cache. If yes, read the data in the memory to obtain the expected row result and return the result to the user. If not, the server process reads the block from the disk to the data buffer cache and caches it. The undo cache block will mirror the block and then read the data in the image to get the row result, the user sees the execution result.

	@ Wentasy