Basic knowledge about Oracle databases

Basic knowledge about Oracle databases

1. components contained in Oracle:
In Oracle, a database refers to the entire Oracle RDBMS environment. It includes the following components:

Each Oracle database runs on a central SYSTEM category and data dictionary. It is located in the SYSTEM tablespace.

Ii. "log"
Oracle databases use several structures to protect data: database backup, logs, rollback segments, and control files. Here we will take a general look at the "log" as one of the main structures ":
Each Oracle database instance provides logs to record all modifications made in the database. Each running Oracle database instance has an online log, which works with the Oracle background process LGWR and immediately records all modifications made to the instance. Offline archiving) logs are optional. Once an Oracle database instance is filled with online logs, an online log archive file can be formed. Archived online log files are uniquely identified and merged into archived logs.
Online logs: each instance of an Oracle database has an associated online log. An online log consists of multiple online log files. Online log file (online redo log file) is filled with the log item redo entry). The data recorded in the log item is used to reconstruct all modifications made to the database.
Archive logs: Archive logs must be created when Oracle wants to archive a full online log file group ). It is useful for database backup and recovery:
<1> database backup and online and archive log files Ensure that all submitted items can be recovered in case of an operating system or disk failure.
<2> online backup can be used if the archived logs are permanently saved when the database is enabled and normally used by the system.
Databases can run in NOARCHIVELOG or ARCHIVELOG modes. When a database is used in NOARCHIVELOG mode, online logs cannot be archived. If the database runs in ARCHIVELOG mode, you can archive online logs.
Iii. physical and logical storage structure:
Oracle RDBMS is composed of tablespaces, and tablespaces are composed of data files. The tablespace data file is formatted as an internal block unit. The block size is set by DBA when Oracle was first created. It can be changed within the range of 512 to 8192 bytes. When an object is created in an Oracle tablespace, the user uses the initial length (initial extent), the next length (next extent), and the minimum length (min extents) and max extents) to indicate the size of the object space. The length of an Oracle database can be changed, but it must contain a chain consisting of at least five consecutive blocks.
4. The connection protocols for Oracle and Microsoft SQL Server:

The above is what I want to introduce you to some basic knowledge about Oracle databases. I believe this knowledge is meaningful for some beginners, from here, you can learn the most basic knowledge of Oracle databases and lay a good foundation to learn more about Oracle databases.