Shortcuts to Oracle physical structure applications

The following articles mainly describe the actual application of the Oracle physical structure and the overview of its basic concepts and the description of related data files. The following describes the specific solution, I hope you will be helpful in your future study after browsing.

Data Files

Each Oracle database has one or more physical data files. database information (structure, data) is stored in these data files, these files can be interpreted and managed only by the Oracle physical structure. oracle data files have the following features:

1. A data file is associated with only one database. The correspondence between the data file and the database is one-to-one. Of course, the relationship between the database and the data file is one-to-many.

2. data files can be automatically expanded. When more storage space is required for data storage, the data stored in the data increases as the data volume increases, and the data files can also automatically grow to meet data storage needs.

3. one or more data files form a logical unit called a tablespace. the correspondence between data files and tablespaces is also a one-to-one relationship. Of course, the inverse relationship between tablespaces and data files is a one-to-many relationship.

The data stored in the data file can be read. Of course, the data is stored in a specific memory area of the Oracle database instance. If a user wants to read a table in the database, this user cannot directly read the data files on the physical disk. First, after Oracle accepts this request, it reads the corresponding data from the created location (physical disk) to the memory, in this case, the user can see the data. oracle software explains how Oracle stores and manages data.

If we modify the data at this time, the data will not be immediately written to the disk. The data will not be written to the disk at a specific time. Frequent and immediate write will lead to a reduction in I/O performance.

Oracle will write the data at a specific time.

Control File

Each Oracle database has a control file. this control file is a prerequisite for Oracle to work normally. control Files generally have three functions: one is to record information on the physical disk. 2. Record the logical structure of the Oracle database. iii. Global supervision. it generally includes the following parts:

1. Database Name

2. Data Files and log files are stored on disks.

3. database creation time

If the control file is lost, the Oracle database cannot be started normally. Theoretically, it can only be started to the MOUNT state. Because the control file is so important, the Oracle physical structure allows multiple control files to be mirrored at the same time.

When the database is started, the data and log files in the control file must be read by the Oracle process. database structure changes are also recorded in the control file at any time. the control file also plays a significant role in Oracle recovery.

Redo log files

Each Oracle Database contains at least two or more groups of redo log files. redo log files record data changes. is to record a continuous change process. in fact, the control also records the Oracle Change process, but both of them are quite different. The control records the changes in the database architecture. the redo log file also records the changes of an architecture, but it records the changes of data in a more detailed database. this information is mainly used for database recovery operations.

Archive log files

This is because Oracle databases record this information as long as they redo log files. however, if the information is permanently saved when the record is fixed, the saved "log" will be called as archiving logs. of course, if the database is running in archive mode and the data is not running in archive mode, redo the log and write it cyclically.

Parameter file

Because Oracle data is composed of two parts: database and instance. A database architecture is recorded by a control file. But what about the instance architecture? These are of course recorded by parameter files. Of course, parameter files also record some features of Oracle software operations, such as whether to archive or not. parameters are extracted from most of the information recorded in the file. However, when the database instance is started, the database is not accessed because the file must be controlled to indicate the physical architecture.

For the transition from a parameter file to an Oracle physical structure, a very important parameter is the control file. this parameter records the location of the control file on the disk. the control file records some information about the data file, log file, and data. from this we can see that the database is started in three stages.

1. The first step is to read the parameter file and start the instance. At this time, the database is not opened. In this status, we often say NOMOUNT.

2. The second step reads the control file according to the parameter file record. At this time, only the control file is read, and the control file has not been explained. Generally, the restoration operation is completed in this step. MOUNT

3. step 3: Read the data file and control file based on the information in the control file. of course, at this time, the information recorded on the disk and the control file itself are checked. if it fails, a problem occurs and the database needs to be restored. (Of course, this step is required. We think that if either of them is started normally, the data will become very messy and the user's data will be lost or lost, this is terrible, and we can see that the interpretation control file is to check the database integrity.) If the comparison is successful, the database can be OPEN.

Alarm log

For data, the operation record instance and database information both have corresponding record information. But if there is a problem in our operation or the database itself is faulty, who will record these problems? An alarm log is usually required to record this information. If no alarm log is available, we do not know any problems that occur when the database is running.

For example. the control file is only reviewed at the beginning of database startup. if I ask you to start it, but I don't care about the problems in the database running process, but who cares? Of course, it is the alarm log. It should always be accompanied by the database to record some data health problems.

Backup File

It is safe for databases to only archive logs. Sometimes backup is required. The backup file is the backup part of the archive logs, but it is very powerful. It is a file generated by the Oracle management tool, you can also perform cold backup. management tools manage database security and backup. They reflect the possession of backup files. the format that can be interpreted only by a specific Oracle physical structure tool. used for disaster recovery (for example, with no archive.