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Updated on 2022-07-29 GMT+08:00
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Archiving

archive_mode

Parameter description: When archive_mode is enabled, completed WAL segments are sent to archive storage by setting archive_command.

Type: SIGHUP

Value range: Boolean

  • on: The archiving is enabled.
  • off: The archiving is disabled.

Default value: off

When wal_level is set to minimal, archive_mode cannot be used.

archive_command

Parameter description: Specifies the command used to archive WALs set by the administrator. You are advised to set the archive log path to an absolute path.

Type: SIGHUP

Value range: a string

Default value: (disabled)

  • Any %p in the string is replaced with the absolute path of the file to archive, and any %f is replaced with only the file name. (The relative path is relative to the data directory.) Use %% to embed an actual % character in the command.
  • This command returns zero only if it succeeds. Example: 
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    archive_command = 'cp --remove-destination %p /mnt/server/archivedir/%f' 
archive_command = 'copy %p /mnt/server/archivedir/%f'  # Windows
  • --remove-destination indicates that files will be overwritten during the archiving.
  • When archive_mode is set to on or not specified, a backup folder will be created in the pg_xlog directory and WALs will be compressed and copied to the pg_xlog/backup directory.

max_xlog_backup_size

Parameter description: Specifies the size of WAL logs backed up in the pg_xlog/backup directory.

Type: SIGHUP

Value range: an integer between 1048576 and 104857600. The unit is KB.

Default value: 2097152

  • The max_xlog_backup_size parameter setting takes effect only when archive_mode is enabled and archive_command is set to NULL.
  • The system checks the size of backup WALs in the pg_xlog/backup directory every minute. If the size exceeds the value specified by max_xlog_backup_size, the system deletes the earliest backup WALs until the size is less than the max_xlog_backup_size value × 0.9.

archive_timeout

Parameter description: Specifies the archiving period.

Type: SIGHUP

Value range: an integer ranging from 0 to INT_MAX. The unit is second. 0 indicates that archiving timeout is disabled.

Default value: 0

  • The server is forced to switch to a new WAL segment file with the period specified by this parameter.
  • Archived files that are closed early due to a forced switch are still of the same length as completely full files. Therefore, a very short archive_timeout will bloat the archive storage. You are advised to set archive_timeout to 60s.
Parent topic: Write Ahead Logs