update postgres backup process

postgres.md

@@ -71,7 +71,7 @@ changed since the first backup.
 
 - to enable WAL archiving:
 
-   1. set `wal_level` to `archive` (or `hot_standby`)
+   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
 
@@ -101,34 +101,11 @@ changed since the first backup.
    
    1. make a base backup
 
-### make a base backup
+### make a base backup[^pg_basebackup]
 
-1. ensure WAL archiving is enabled and working
+1. ensure that WAL archiving is working and set up properly.
-2. issue the following command as superuser:
+1. Run `pg_basebackup -D - -F tar > backup.tar`
 
-   ```
-   SELECT pg_start_backup('label');
-   ```
-
-   - `label` is any string to uniquely identify backup operation, e.g. the full path where you
-      intend to put the backup dump file
-   - It does not matter which database within the cluster you connect to to issue this command
-3. Perform the backup, using any convenient file-system-backup tool such as tar or cpio
-   (not pg_dump or pg_dumpall). It is neither necessary nor desirable to stop normal operation of
-   the database while you do this.
-4. issue the following command as superuser:
-
-   ```
-   SELECT pg_stop_backup();
-   ```
-
-   this terminates the backup mode and performs an automatic switch to the next WAL segment
-
-
-> You can also use the pg_basebackup tool to take the backup, instead of manually copying the files.
-  This tool will do the equivalent of pg_start_backup(), copy and pg_stop_backup() steps
-  automatically, and transfers the backup over a regular PostgreSQL connection using the replication
-  protocol, instead of requiring file system level access. pg_basebackup does not interfere with
-  file system level backups taken using pg_start_backup()/pg_stop_backup().
 
 [^c24]: https://www.postgresql.org/docs/9.1/backup-dump.html
+[^pg_basebackup]: https://www.postgresql.org/docs/13/app-pgbasebackup.html