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