Interactive Demo

Backup and Recovery: Single-Server Streaming - Running a Base Backup

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With the Barman server configured in our last step, we can run a full backup (or "base backup").

This demo is interactive

You can follow along right in your browser. When you click "Start Now," Katacoda will load a Docker Compose environment with two container images representing a PostgreSQL 13 server with the Pagila database loaded (named pg) and a backup server for Barman (named backup).

Once you see a barman@backup prompt, you can follow the steps below.

console
Clicking Start Now will load an interactive terminal in this window

To run a full backup, we use Barman's backup command:

barman backup pg --wait
Output
Starting backup using postgres method for server pg in /var/lib/barman/pg/base/20210329T235157
Backup start at LSN: 0/3000000 (000000010000000000000002, 00000000)
Starting backup copy via pg_basebackup for 20210329T235157
Copy done (time: 1 second)
Finalising the backup.
This is the first backup for server pg
WAL segments preceding the current backup have been found:
        000000010000000000000002 from server pg has been removed
Backup size: 38.3 MiB
Backup end at LSN: 0/4000000 (000000010000000000000003, 00000000)
Backup completed (start time: 2021-03-29 23:51:57.146435, elapsed time: 2 seconds)
Waiting for the WAL file 000000010000000000000003 from server 'pg'
Processing xlog segments from streaming for pg
        000000010000000000000003

The --wait option causes Barman to wait for arrival and processing of the WAL file corresponding to the end of the backup, to ensure the backup is complete before the command returns.

Note

Since the cron job is doing this periodically in the background, the WAL segments you see listed may be different than the output listed above!

Verify that it completed by listing backups for the server:

barman list-backup pg
Output
pg 20210329T235157 - Mon Mar 29 23:51:59 2021 - Size: 54.3 MiB - WAL Size: 0 B

(the timestamps will be different for you)

Of course, we've configured streaming backups - so we shouldn't need to depend on having a base backup for every change made to the database. Let's make a small modification to the data and verify that it arrives.

First, log into the database (we'll use our barman user for convenience in this demonstration):

psql -h pg -d pagila -U barman
Output
psql (13.2 (Ubuntu 13.2-1.pgdg20.04+1))
Type "help" for help.

Then make a modifications, and view the results:

Update actor Set first_name='ALOYSIUS' where actor_id=23;
Select * From actor Where last_name='KILMER';
\q
Output
UPDATE 1
 actor_id | first_name | last_name |          last_update          
----------+------------+-----------+-------------------------------
       45 | REESE      | KILMER    | 2020-02-15 09:34:33+00
       55 | FAY        | KILMER    | 2020-02-15 09:34:33+00
      153 | MINNIE     | KILMER    | 2020-02-15 09:34:33+00
      162 | OPRAH      | KILMER    | 2020-02-15 09:34:33+00
       23 | ALOYSIUS   | KILMER    | 2021-03-29 23:53:22.302271+00
(5 rows)

Ok, let's see if it showed up:

grep 'ALOYSIUS' ~/pg/streaming/*
Output
Binary file /var/lib/barman/pg/streaming/000000010000000000000004.partial matches

There it is! The current WAL segment hasn't been rotated yet, but we have the most recent data in the partial WAL streamed to Barman. So in theory, nothing would be lost of something terrible happened to the database right now...

Now, the crucial question with backups is always the same: "can you get the data back?"

We'll answer this in Step #4: Restoring a Backup.


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