Unable to create a backup of PostgreSQL database: pg_dump: aborting because of server version mismatch

Symptoms

• The Plesk server has two PostgreSQL database servers installed, with the versions 9.2.15 and 9.5.4.
• At least one database was created on the PostgreSQL server with version 9.5.4.
• Attempting to create a backup in Tools & Settings > Backup Manager, the process fails with the error below:

  WARNING: (postgresql object 'admin_db') Failed to execute backup database
  WARNING: (postgresql object 'admin_db') Not all the data was backed up into /var/lib/psa/dumps/domains/example.com/databases/admin_db_4 successfully. pg_dump: server version: 9.5.4; pg_dump version: 9.2.15
  pg_dump: aborting because of server version mismatch

• As result the created backup does not include the database from PostgreSQL server with version 9.5.4.

Cause

Plesk bug with the ID PPPM-5078, which will be fixed in future updates.

Resolution

Until the bug be fixed, as workaround:

1. Log into the server via SSH.
2. Create a backup for the /etc/psa/psa.conf file:

   # cp -a /etc/psa/psa.conf{,.back}

3. Edit the /etc/psa/psa.conf file to point Plesk to the new PostgreSQL database server by changing the lines below from: 

   PGSQL_DATA_D /var/lib/pgsql/data
   PGSQL_CONF_D /var/lib/pgsql/data
   PGSQL_BIN_D /usr/bin

   To

   PGSQL_DATA_D /var/lib/pgsql/9.5/data
   PGSQL_CONF_D /var/lib/pgsql/9.5/data
   PGSQL_BIN_D /usr/pgsql-9.5/bin