From the objective of OSS-DB Exam Silver
- Operation and Management - Backup Method (File System Level Backup and Restore)
Sample Question
1.16
I want to create a backup by physically copying the file system that constitutes the database. Choose the most appropriate description.
- Database files are upward compatible, so you can restore files copied in PostgreSQL 9.1 environment to PostgreSQL 9.2 environment.
- For example, if the name of the physical file that makes up the table called test is 10001, you can use the same table by copying this file to another database environment.
- Compared with the logical backup acquired by pg_dump, backup by file system copy is generally fast.
- Compared with the logical backup acquired by pg_dump, backup by file system copy is generally smaller in size.
- When acquiring a backup, the database can be kept running.
※This sample exam is different from those that appear in the actual OSS-DB Exam.
2019/03/04
Answer and Explanation
There are various ways to back up the database. Physically copying all the files in the directory of the database cluster is the most fundamental backup method, but since the database must be stopped, whether it is practical or not depends on environmental restrictions.
Database clusters are incompatible between major versions. For example, if you copy files of 9.1 database cluster and restore to 9.2 environment, it can not be used.
Also, with this method you need to back up the entire database cluster and you can not retrieve and copy only some tables.
Compared to logical backup by pg_dump, simple file copy is generally faster because pg_dump needs to read the file, extract its contents and output it. However, since pg_dump does not output the contents of the index etc., the file copy will be larger in size.
Therefore, the correct answer is C.