Restore Backup using pg_basebackup in PostgreSQL


Restore Backup using pg_basebackup in PostgreSQL


In this blog, we will see How to perform a restore of a backup taken from pg_basebackup. We will see full steps for the below two scenarios:

1. Restore in the same directory structure of the backup database.
2. Restore in the different directory structures of the backup database
.

For the purpose of demonstration, we will be using our second PostgreSQL Cluster created on Port: 5433 Click here to learn How to create a second PostgreSQL Cluster. For pg_basebackup backup commands Click here to read more.


PostgreSql Cluster Physical Structure: PostgreSQL Cluster data directory: /u01/psql-13, Created two non-default tablespaces myts03: /u01/psql3_tbls & myts04: /u01/psql4_tbls. Created two sample database sample3 & sample4 & loaded them with sample data. And configured WAL archiving: /u01/wal_archive.

postgres=# show data_directory;
 data_directory
----------------
 /u01/psql-13

postgres=#  \db+
                                      List of tablespaces
    Name    |  Owner   |    Location     | Access privileges | Options |  Size   | Description
------------+----------+-----------------+-------------------+---------+---------+-------------
 myts03     | postgres | /u01/psql3_tbls |                   |         | 0 bytes |
 myts04     | postgres | /u01/psql4_tbls |                   |         | 0 bytes |
 pg_default | postgres |                 |                   |         | 46 MB   |
 pg_global  | postgres |                 |                   |         | 559 kB  |
(4 rows)


postgres=# \l+
                                                                    List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges   |  Size   | Tablespace |                Description
-----------+----------+----------+-------------+-------------+-----------------------+---------+------------+--------------------------------------------
 dvdrental | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =Tc/postgres         +| 15 MB   | pg_default |
           |          |          |             |             | postgres=CTc/postgres+|         |            |
           |          |          |             |             | read_only=c/postgres  |         |            |
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |                       | 15 MB   | pg_default | default administrative connection database
 sample3   | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |                       | 15 MB   | myts03     |
 sample4   | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |                       | 15 MB   | myts04     |
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +| 7969 kB | pg_default | unmodifiable empty database
           |          |          |             |             | postgres=CTc/postgres |         |            |
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +| 8117 kB | pg_default | default template for new databases
           |          |          |             |             | postgres=CTc/postgres |         |            |
(6 rows)

postgres=#

postgres=# select name,setting,unit from pg_settings where name in ('archive_mode','archive_command','archive_timeout');
      name       |                          setting                           | unit
-----------------+------------------------------------------------------------+------
 archive_command | test ! -f /u01/wal_archive/%f && cp %p /u01/wal_archive/%f |
 archive_mode    | on                                                         |



Create and Load test table and Switch WAL File: Let’s Create Table T_TEST and insert 1000 random records. Once the insert operation is done do force the WAL switch to make sure all changes are archived.

postgres=# \connect sample3
You are now connected to database "sample3" as user "postgres".
sample3=#
sample3=# create table t_Test (slno integer, ts timestamp);
CREATE TABLE
sample3=# insert into t_test values (generate_series(1,1000),now());
INSERT 0 1000
sample3=#
sample3=# select count(*) from t_test;
 count
-------
  1000
(1 row)

sample3=# \connect sample4
You are now connected to database "sample4" as user "postgres".
sample4=#
sample4=# create table t_Test (slno integer, ts timestamp);
CREATE TABLE
sample4=# insert into t_test values (generate_series(1,1000),now());
INSERT 0 1000
sample4=# select count(*) from t_test;
 count
-------
  1000
(1 row)

postgres=# select pg_switch_wal();
 pg_switch_wal
---------------
 0/A04DDC8
(1 row)

postgres=#
postgres=#


Full DB backup: Perform full cluster level tar backup using pg_basebackup using the below command.

-bash-4.2$ pg_basebackup -h localhost -p 5433 -U postgres -D /u01/backup/latest1_backup -Ft -z -Xs -P
78382/78382 kB (100%), 3/3 tablespaces
-bash-4.2$

-bash-4.2$ ls -ltr /u01/backup/latest1_backup
total 12900
-rw-------. 1 postgres postgres 2699207 Jul  4 16:16 21913.tar.gz
-rw-------. 1 postgres postgres 2699006 Jul  4 16:16 21914.tar.gz
-rw-------. 1 postgres postgres 7453080 Jul  4 16:16 base.tar.gz
-rw-------. 1 postgres postgres   17655 Jul  4 16:16 pg_wal.tar.gz
-rw-------. 1 postgres postgres  334189 Jul  4 16:16 backup_manifest
-bash-4.2$


Stop PostgreSQL Cluster and remove all datafiles: Let simulate the failure and delete all datafiles we have from the base and tablespaces directory.

[root@test-machine02 ~]# systemctl stop psql-13.service
[root@test-machine02 ~]# rm -rf /u01/psql-13/*
[root@test-machine02 ~]# rm -rf /u01/psql3_tbls/*
[root@test-machine02 ~]# rm -rf /u01/psql4_tbls/*


Restore in same directory structure as of backup database


Step 1. Untar Base backup: Use OS command tar to copy the base backup to the base location: /u01/psql-13

-bash-4.2$ tar xvf /u01/backup/latest1_backup/base.tar.gz -C  /u01/psql-13
backup_label
tablespace_map
pg_wal/
./pg_wal/archive_status/
global/
global/1262


Step 2. View tablespace_map File: pg_basebackup command creates a text file called tablespace_map which has mapping to tablespace OID and directory location.

-bash-4.2$ pwd
/u01/psql-13
-bash-4.2$ cat tablespace_map
21913 /u01/psql3_tbls
21914 /u01/psql4_tbls
-bash-4.2$


Step 3. Untar Tablespace & WAL Backup: Untar both tablespace backup and WAL backup to its respective location.

-bash-4.2$
-bash-4.2$ tar xvf /u01/backup/latest1_backup/21913.tar.gz -C  /u01/psql3_tbls
PG_13_202007201/
PG_13_202007201/21916/
PG_13_202007201/21916/1255

-bash-4.2$
-bash-4.2$ tar xvf /u01/backup/latest1_backup/21914.tar.gz -C  /u01/psql4_tbls
PG_13_202007201/
PG_13_202007201/21917/
PG_13_202007201/21917/1255

-bash-4.2$
-bash-4.2$ tar xvf /u01/backup/latest1_backup/pg_wal.tar.gz -C /u01/psql-13/pg_wal
00000001000000000000000C
archive_status/00000001000000000000000C.done
-bash-4.2$
-bash-4.2$


Step 4. Update restore_command in postgresql.conf: Edit postgresql.conf file and provide WAL archiving location So postgresql service and do recovery based on available WAL archives.

-bash-4.2$ vi postgresql.conf
restore_command = 'cp /u01/wal_archive/%f %p'           # command to use to restore an archived logfile segment
:wq!

-bash-4.2$ grep restore_command postgresql.conf
restore_command = 'cp /u01/wal_archive/%f %p'           # command to use to restore an archived logfile segment
-bash-4.2$


Step 5. Start PostgreSQL Service: Once all the above steps are done. Start postgresql services.

[root@test-machine02 ~]#
[root@test-machine02 ~]# systemctl start psql-13.service
[root@test-machine02 ~]#


Step 6. Verify logfile: Verify logfile to see everything went fine to restore.

-bash-4.2$ pwd
/u01/psql-13/log
-bash-4.2$ vi postgresql-Sun.log
2021-07-04 16:41:44.044 +03 [47578] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5433"
2021-07-04 16:41:44.047 +03 [47582] LOG:  database system was interrupted; last known up at 2021-07-04 16:16:13 +03
2021-07-04 16:41:44.063 +03 [47582] LOG:  redo starts at 0/C000028
2021-07-04 16:41:44.064 +03 [47582] LOG:  consistent recovery state reached at 0/C000100
2021-07-04 16:41:44.064 +03 [47582] LOG:  redo done at 0/C000100
2021-07-04 16:41:44.132 +03 [47578] LOG:  database system is ready to accept connections


Step 7. Verify Data: Verify all data exists after restore and recovery.

-bash-4.2$
-bash-4.2$ psql -p 5433
psql (13.2)
Type "help" for help.

postgres=#
postgres=# \l
                                  List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
 dvdrental | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =Tc/postgres         +
           |          |          |             |             | postgres=CTc/postgres+
           |          |          |             |             | read_only=c/postgres
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 sample3   | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 sample4   | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
(6 rows)

postgres=#


postgres=# \connect sample3
You are now connected to database "sample3" as user "postgres".
sample3=# select count(*) from t_test;
 count
-------
  1000
(1 row)

sample3=# \connect sample4
You are now connected to database "sample4" as user "postgres".
sample4=# select count(*) from t_test;
 count
-------
  1000
(1 row)

sample4=#



Restore in different directory structure as of backup database


Let assume we are doing a restore in a different server having a directory structure as below.

[root@test-machine02 u01]# mkdir psql-data
[root@test-machine02 u01]# mkdir psql5_tbls
[root@test-machine02 u01]# mkdir psql6_tbls
[root@test-machine02 u01]# chown postgres:postgres psql-data
[root@test-machine02 u01]# chown postgres:postgres psql5_tbls
[root@test-machine02 u01]# chown postgres:postgres psql6_tbls
[root@test-machine02 u01]#

Step 1. Untar Base backup: Untar base backup in base location.

-bash-4.2$ tar xvf /u01/backup/latest1_backup/base.tar.gz -C  /u01/psql-data
backup_label
tablespace_map
pg_wal/
./pg_wal/archive_status/
global/


Step 2. Untar Tablespace & WAL backup: Untar backup of tablespace and WAL backup to its respective location.

-bash-4.2$ tar xvf /u01/backup/latest1_backup/21913.tar.gz -C  /u01/psql5_tbls
PG_13_202007201/
PG_13_202007201/21916/
PG_13_202007201/21916/1255

-bash-4.2$
-bash-4.2$ tar xvf /u01/backup/latest1_backup/21914.tar.gz -C  /u01/psql6_tbls
PG_13_202007201/
PG_13_202007201/21917/
PG_13_202007201/21917/1255
PG_13_202007201/21917/1255_fsm

-bash-4.2$
-bash-4.2$ tar xvf /u01/backup/latest1_backup/pg_wal.tar.gz -C /u01/psql-data/pg_wal
00000001000000000000000C
archive_status/00000001000000000000000C.done
-bash-4.2$


Step 3. Edit tablespace_map file: Edit file tablespace_map and update the new location of tablespaces.

-bash-4.2$ pwd
/u01/psql-data
-bash-4.2$ vi tablespace_map
21913 /u01/psql5_tbls
21914 /u01/psql6_tbls
:wq!


Step 4. Update restore_command in postgresql.conf: Edit postgresql.conf file and provide WAL archiving location So PostgresSQL service do recovery based on available WAL archives. We are providing a new Port 5434 as port 5433 is already in use.

-bash-4.2$ cd /u01/psql-data
-bash-4.2$ vi postgresql.conf
port = 5434  
restore_command = 'cp /u01/wal_archive/%f %p'
:wq!


Step 5. Start Cluster with pg_ctl: Once all the above steps are done. Start PostgreSQL cluster using command pg_ctl, We cannot use systemctl command as service is not registered in systemctl.

-bash-4.2$ /usr/pgsql-13/bin/pg_ctl -D /u01/psql-data  start
waiting for server to start....2021-07-04 17:18:01.072 +03 [49561] FATAL:  data directory "/u01/psql-data" has invalid permissions
2021-07-04 17:18:01.072 +03 [49561] DETAIL:  Permissions should be u=rwx (0700) or u=rwx,g=rx (0750).
 stopped waiting
pg_ctl: could not start server
Examine the log output.
-bash-4.2$


Step 6. Correct permissions: As from the above output we have a folder permission issue. Correct permission with the below commands.

[root@test-machine02 u01]#
[root@test-machine02 u01]# chmod 750 psql-data
[root@test-machine02 u01]#
[root@test-machine02 u01]# ls -ld psql-data
drwxr-x---. 20 postgres postgres 4096 Jul  4 17:12 psql-data
[root@test-machine02 u01]# chmod 750 psql5_tbls
[root@test-machine02 u01]# chmod 750 psql6_tbls
[root@test-machine02 u01]#


Step 7. Start Cluster again with pg_ctl: Let try to start the PostgreSQL cluster once again using pg_ctl utility.

-bash-4.2$ /usr/pgsql-13/bin/pg_ctl -D /u01/psql-data  start
waiting for server to start....2021-07-04 17:20:07.510 +03 [49688] LOG:  redirecting log output to logging collector process
2021-07-04 17:20:07.510 +03 [49688] HINT:  Future log output will appear in directory "log".
 done
server started
-bash-4.2$


Step 8. Verify logfile: Verify logfile to confirm everything is fine.

-bash-4.2$ pwd
/u01/psql-data/log
-bash-4.2$
-bash-4.2$ vi postgresql-Sun.log
2021-07-04 17:20:07.510 +03 [49688] LOG:  starting PostgreSQL 13.2 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44), 64-bit
2021-07-04 17:20:07.512 +03 [49688] LOG:  listening on IPv6 address "::1", port 5434
2021-07-04 17:20:07.512 +03 [49688] LOG:  listening on IPv4 address "127.0.0.1", port 5434
2021-07-04 17:20:07.513 +03 [49688] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5434"
2021-07-04 17:20:07.514 +03 [49688] LOG:  listening on Unix socket "/tmp/.s.PGSQL.5434"
2021-07-04 17:20:07.516 +03 [49690] LOG:  database system was interrupted; last known up at 2021-07-04 16:16:13 +03
2021-07-04 17:20:07.531 +03 [49690] LOG:  redo starts at 0/C000028
2021-07-04 17:20:07.531 +03 [49690] LOG:  consistent recovery state reached at 0/C000100
2021-07-04 17:20:07.531 +03 [49690] LOG:  redo done at 0/C000100
2021-07-04 17:20:07.551 +03 [49688] LOG:  database system is ready to accept connections


Step 9. Verify Data: Verify all data exists after restore and recovery.

-bash-4.2$
-bash-4.2$ psql -p 5434
psql (13.2)
Type "help" for help.

postgres=# \conninfo
You are connected to database "postgres" as user "postgres" via socket in "/var/run/postgresql" at port "5434".
postgres=#
postgres=# \l
                                  List of databases
   Name    |  Owner   | Encoding |   Collate   |    Ctype    |   Access privileges
-----------+----------+----------+-------------+-------------+-----------------------
 dvdrental | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =Tc/postgres         +
           |          |          |             |             | postgres=CTc/postgres+
           |          |          |             |             | read_only=c/postgres
 postgres  | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 sample3   | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 sample4   | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 |
 template0 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
 template1 | postgres | UTF8     | en_US.UTF-8 | en_US.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
(6 rows)

postgres=# \connect sample3
You are now connected to database "sample3" as user "postgres".
sample3=# select count(*) from t_test;
 count
-------
  1000
(1 row)

sample3=# \connect sample4
You are now connected to database "sample4" as user "postgres".
sample4=# select count(*) from t_test;
 count
-------
  1000
(1 row)

sample4=#



This document is just for learning purpose and always validate in the LAB environment first before applying in the LIVE environment.


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