113 lines
3.7 KiB
Markdown
Executable File
113 lines
3.7 KiB
Markdown
Executable File
---
|
|
author: Alvie Rahman
|
|
date: \today
|
|
title: Postgres
|
|
tags: [ programming ]
|
|
---
|
|
|
|
\tableofcontents
|
|
|
|
# Chapter 24: Backup and Restore[^c24]
|
|
|
|
Three types of backups:
|
|
|
|
- SQL dump---create text file of SQL commands that can recreate the database
|
|
|
|
`pg_dump dbname > outfile`
|
|
|
|
To restore: `psql dbname < infile`
|
|
|
|
- must be run as database superuser
|
|
- can be run remotely
|
|
- set host and username with `-h` and `-U` switches
|
|
|
|
- File system level backup
|
|
|
|
`tar -cf backup.tar /usr/local/pgsql/data`
|
|
|
|
- The database server **must** be shut down
|
|
- You can only backup and restore entire database clusters
|
|
|
|
- Continuous archiving (write ahead log archiving)
|
|
|
|
- "We do not need a perfectly consistent file system backup as the starting point."
|
|
- method can be used to create a continuous backup
|
|
- supports point in time recovery
|
|
- can be used to create a warm standby system
|
|
|
|
- can only be used to restore an entire database cluster
|
|
- requires a lot of archival storage
|
|
|
|
## SQL Dump
|
|
|
|
### Restoring a dump
|
|
|
|
Important note before you restore a database:
|
|
|
|
> Before restoring an SQL dump, all the users who own objects or were granted permissions on objects
|
|
in the dumped database must already exist. If they do not, the restore will fail to recreate the
|
|
objects with the original ownership and/or permissions. (Sometimes this is what you want, but
|
|
usually it is not.)
|
|
|
|
You should probably read the whole document [here](https://www.postgresql.org/docs/9.1/backup-dump.html)
|
|
|
|
## File system backup
|
|
|
|
You can run a FS level backup with minimal downtime with `rsync`:
|
|
|
|
1. Perform a backup with `rsync` while system is live
|
|
2. Shut down database server
|
|
3. Rerun `rsync` backup command
|
|
4. Restart database server
|
|
|
|
The second `rsync` command will run significantly quicker as it only has to transfer what has
|
|
changed since the first backup.
|
|
|
|
## Write Ahead Log (WAL) archiving
|
|
|
|
- WAL segment files usually get "recycled" by being renamed
|
|
- to archive WAL data, the content of each segment is captured and saved before it is reused
|
|
|
|
- you can save the data any way you like
|
|
|
|
- to enable WAL archiving:
|
|
|
|
1. set `wal_level` to `replica` or higher
|
|
1. set `archive_mode` to `on`
|
|
1. set `archive_command` to the command to use to backup
|
|
|
|
- e.g.
|
|
|
|
```
|
|
archive_command = 'test ! -f /mnt/server/archivedir/%f && cp %p /mnt/server/archivedir/%f' # Unix
|
|
archive_command = 'copy "%p" "C:\\server\\archivedir\\%f"' # Windows
|
|
```
|
|
|
|
where `%f` is the filename of the file to archive and `%p` is the path of file to archive:
|
|
|
|
```
|
|
test ! -f /mnt/server/archivedir/00000001000000A900000065 && cp pg_xlog/00000001000000A900000065 /mnt/server/archivedir/00000001000000A900000065
|
|
```
|
|
|
|
- The command must only ever return a exit status of 0 **only if it succeeds*
|
|
|
|
- postgres will recycle the file if the command returns 0
|
|
|
|
- The archived data should have minimal access permissions
|
|
- the archive command should generally refuse to overwrite files and return non-zero
|
|
- In writing your archive command, you should assume that the file names to be archived can be
|
|
up to 64 characters long and can contain any combination of ASCII letters, digits, and dots.
|
|
- It is not necessary to preserve the original relative path (`%p`) but it is necessary to
|
|
preserve the file name (`%f`).
|
|
|
|
1. make a base backup
|
|
|
|
### make a base backup[^pg_basebackup]
|
|
|
|
1. ensure that WAL archiving is working and set up properly.
|
|
1. Run `pg_basebackup -D - -F tar > backup.tar`
|
|
|
|
|
|
[^c24]: https://www.postgresql.org/docs/9.1/backup-dump.html
|
|
[^pg_basebackup]: https://www.postgresql.org/docs/13/app-pgbasebackup.html
|