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This article focuses on "what is the principle of Oracle crash recovery". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "what is the principle of Oracle crash recovery"?

1. Application scenario

When the database instance is running, there are many dirty data blocks in the buffer cache in the in-memory SGA. These data blocks are not written to the hard disk. At this point, the server suddenly lost power, and the data in memory was immediately gone. Data loss occurs at this point.

two。 Classification of lost data

(1) data that can be lost

Data that is not submitted is data that can be lost.

(2) data that cannot be lost

Data that has been submitted cannot be lost.

3. After the Oracle instance crashes, the block in which the data has been submitted in the buffer cache needs to be recovered. Get it back through what? That's the journal!

After the Commit command is executed, Oracle only does one thing, which is to transfer the log from the log buffer to the disk log file. So the data in buffer cache can be constructed from data files on disk and logs on disk.

4. After the Oracle instance crashes, it will automatically find that the instance is shut down abnormally when it is started next time. At this point, Oracle will automatically restore the instance crash. Instance crash recovery uses data files on disk and log files on disk to construct data blocks constructed at the moment of database crash.

5. The logs used include the current log, not the archive log.

At this point, I believe you have a deeper understanding of "what is the principle of Oracle crash recovery". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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