Oracle Learning Experience __oracle

First, positioning
Oracle is divided into two pieces, one is development, the other is management. Development is mainly written to write stored procedures, triggers, and so on, as well as using Oracle's develop tool to do form. Sort of like a programmer, need to have a strong logical thinking and creative ability, personally think will be more hard, is the youth Rice J; management requires a deep understanding of the principles of Oracle database, the ability to control the overall situation and close thinking, responsibility is greater, because a small error will down the entire database, In contrast to the former, the latter value experience more.
　　
Because of the heavy responsibility of database management, few companies are willing to ask someone who has just contacted Oracle to manage the database. For young people who have just graduated, you can choose to do the development, have a certain experience after the transformation, to do the management of the database. Of course, this still depends on the actual situation of people to decide.
　　
Second, learning methods
My method is simple: reading, thinking, writing notes, doing experiments, thinking again, writing notes
　　
After reading the theory of Things, calm down to think, ask yourself a few why, and then learn and think of the knowledge point to make a note, in the confusion or doubt, do the experiment, think how it will be, the same, the results of the experiment down. To think and do experiments is to get a deeper understanding of this knowledge point. The process of taking notes is also the process of clearing up your own thinking.
　　
The process of learning is to make a problem from fuzzy to clear, and then from clear to fuzzy process. And every change means you've learned a new point of knowledge.
　　
The process of learning is also from point to line, from line to net, from the network to the surface of the process. When the point becomes a line, you will have a feeling of always being enlightened. When the net to face, you are the master of the
　　
A lot of netizens, especially beginners, a problem to get the forum to ask, before asking, you have checked the book, have you ever studied, there is no search forum. This is called thinking inertia, no study attitude, no matter what things, will not succeed.
　　
Third, Oracle's system
Oracle's system is huge, and to learn it, you first need to understand Oracle's framework. Here, give a brief introduction to Oracle's architecture, giving beginners a holistic understanding of Oracle.
　　
1. Physical structure (composed of control file, data file, redo log file, parameter file, archive file, password file)
Control files: Contains the necessary information to maintain and validate database integrity, for example, control files are used to identify data files and redo log files, and a database requires at least one control file
Data files: Files that store data
Redo log file: Contains a record of changes made to the database so that data recovery can be enabled in the event of a failure. A database requires at least two redo log files
Parameter file: Defines the attributes of an Oracle routine, for example, it contains parameters to resize some memory structures in the SGA
Archive: An offline copy of the redo log files that may be necessary for recovery from media failure.
Password files: Authenticating which users have permission to start and close Oracle routines
　　
2. Logical Structure (table space, segment, area, block)
Tablespace: The basic logical structure of a database, a collection of data files.
Segment: Is the space occupied by the object in the database
Area: A large storage space reserved for data one-time
Block: Oracle's most basic storage unit, specified when establishing a database
　　
3. Memory allocation (SGA and PGA)
SGA: The memory area that is used to store database information that is shared by the database process. It contains data and control information for the Oracle server, which is allocated in real memory on the computer where the Oracle server resides, if the actual memory is not enough to write to virtual memory.
PGA: Data and control information that contains a single server process or a single background process, the SGA that is shared with several processes the PGA is an area that is used by only one process, and the PGA is allocated at the time the process is created to recycle when the process is terminated
　　
4. Background process (data write process, log write process, system monitoring, process monitoring, checkpoint process, archive process, service process, user process)
Data write process: Responsible for writing changed data from the database buffer cache to the data file
Log Write process: Write changes in redo log buffers to online redo log files
System monitoring: Checking the consistency of the database if necessary, you will also start the recovery of the database when the database is open
Process monitoring: Responsible for cleaning up resources when an Oracle process fails
Checkpoint process: is responsible for updating database state information in control files and data files whenever changes in the buffer cache are permanently recorded in the database.
Archiving process: Backing up or archiving a full log group for each log switch
Service process: User process Service.
User process: At the client, responsible for passing the user's SQL statement to the service process and getting the query data back from the server segment.
　　
5. Oracle Routines: The Oracle routines consist of a SGA memory structure and a background process for managing the database. Routines can only open and use one database at a time.
　　
6. SCN (System change number): A serial number, which is maintained by the system, is changed. When the system needs to be updated automatically increases, he is the system to maintain data consistency and sequential recovery of important signs.
　　
Iv. further study
Management: You can test the OCP certificate, the Oracle first has a systematic study, and then look at Oracle Concepts, Oracle online document, Oracle will have a more in-depth understanding of the principles, and can begin to do some research topics such as: RMAN, RAS, Statspact, DATAGUARD, tuning, Backup&recover, and so on.
　　
Development: For Oracle developers, after learning Oracle's basic architecture, focus on the Pl/sql and Oracle Development tools section. Pl/sql mainly includes how to write SQL statements, how to use the functions of Oracle itself, how to write stored procedures, storage functions, triggers, and so on. Oracle's development tools are primarily Oracle's own Developer Suite (Oracle Forms Developer and Reports Developer), and learn how to use these tools skillfully.

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