Fetch wal_keep_size, not wal_keep_segments, from Postgres 13

The `wal_keep_segments` parameter introduced in v9.0 was replaced with
`wal_keep_size` in v13. Running Barman against Postgres 13 resulted in
errors like the following being logged:

    barman ERROR:  unrecognized configuration parameter "wal_keep_segments"
    barman STATEMENT:  SHOW "wal_keep_segments"

Here we change fetch_remote_status() to ask for wal_keep_size if the
server version is >= 13. We didn't use this value anywhere, so we don't
need any further changes to adapt to the different return value.

Signed-off-by: Abhijit Menon-Sen <ams@2ndQuadrant.com>

barman/postgres.py

@@ -827,7 +827,12 @@ def fetch_remote_status(self):
                 pg_settings.append('wal_level')
                 pg_settings.append('hot_standby')
                 pg_settings.append('max_wal_senders')
-                pg_settings.append('wal_keep_segments')
+                # Retrieve wal_keep_segments from version 9.0 onwards, until
+                # version 13.0, where it was renamed to wal_keep_size
+                if self.server_version < 130000:
+                    pg_settings.append('wal_keep_segments')
+                else:
+                    pg_settings.append('wal_keep_size')
 
             if self.server_version >= 90300:
                 pg_settings.append('data_checksums')

doc/manual/42-server-commands.en.md

@@ -198,7 +198,8 @@ record of the transaction log. When the status file needs to be
 cleaned, the `--reset` option can be used.
 
 > **IMPORTANT:** If you are not using replication slots, you rely
-> on the value of `wal_keep_segments`. Be aware that under high peeks
+> on the value of `wal_keep_segments` (or `wal_keep_size` from
+> PostgreSQL version 13.0 onwards). Be aware that under high peaks
 > of workload on the database, the `receive-wal` process
 > might fall behind and go out of sync. As a precautionary measure,
 > Barman currently requires that users manually execute the command with the

tests/test_postgres.py

@@ -822,6 +822,8 @@ def test_current_xlog_file_name(self, is_in_recovery_mock, conn_mock):
            new_callable=PropertyMock)
     @patch('barman.postgres.PostgreSQLConnection.is_in_recovery',
            new_callable=PropertyMock)
+    @patch('barman.postgres.PostgreSQLConnection.has_backup_privileges',
+           new_callable=PropertyMock)
     @patch('barman.postgres.PostgreSQLConnection.is_superuser',
            new_callable=PropertyMock)
     @patch('barman.postgres.PostgreSQLConnection.server_txt_version',
@@ -847,6 +849,7 @@ def test_get_remote_status(self,
                                has_pgespresso_mock,
                                server_txt_version_mock,
                                is_superuser_mock,
+                               has_backup_privileges_mock,
                                is_in_recovery_mock,
                                archive_timeout_mock,
                                checkpoint_timeout_mock,
@@ -867,6 +870,7 @@ def test_get_remote_status(self,
         has_pgespresso_mock.return_value = True
         server_txt_version_mock.return_value = '9.5.0'
         is_in_recovery_mock.return_value = False
+        has_backup_privileges_mock.return_value = True
         is_superuser_mock.return_value = True
         get_configuration_files_mock.return_value = {'a': 'b'}
         get_synchronous_standby_names_mock.return_value = []
@@ -885,6 +889,7 @@ def test_get_remote_status(self,
             'max_replication_slots': 'a max_replication_slots value',
             'wal_compression': 'a wal_compression value',
             'wal_keep_segments': 'a wal_keep_segments value',
+            'wal_keep_size': 'a wal_keep_size value',
         }
 
         get_setting_mock.side_effect = lambda x: settings.get(x, 'unknown')
@@ -948,6 +953,36 @@ def test_get_remote_status(self,
             'postgres_systemid': 6721602258895701769,
         }
 
+        # Test PostgreSQL 13
+        conn_mock.return_value.server_version = 130000
+        result = server.postgres.fetch_remote_status()
+        assert result == {
+            'a': 'b',
+            'is_superuser': True,
+            'has_backup_privileges': True,
+            'is_in_recovery': False,
+            'current_lsn': 'DE/ADBEEF',
+            'current_xlog': '00000001000000DE00000000',
+            'data_directory': 'a directory',
+            'pgespresso_installed': True,
+            'server_txt_version': '9.5.0',
+            'wal_level': 'a wal_level value',
+            'current_size': 497354072,
+            'replication_slot_support': True,
+            'replication_slot': None,
+            'synchronous_standby_names': [],
+            'archive_timeout': 300,
+            'checkpoint_timeout': 600,
+            'wal_keep_size': 'a wal_keep_size value',
+            'hot_standby': 'a hot_standby value',
+            'max_wal_senders': 'a max_wal_senderse value',
+            'data_checksums': 'a data_checksums',
+            'max_replication_slots': 'a max_replication_slots value',
+            'wal_compression': 'a wal_compression value',
+            'xlog_segment_size': 8388608,
+            'postgres_systemid': 6721602258895701769,
+        }
+
         # Test error management
         server.postgres.close()
         conn_mock.side_effect = psycopg2.DatabaseError