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Enhanced sync connections check (#2524)

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When `synchronous_standby_names` GUC is changed PostgreSQL nearly immediately starts reporting corresponding walsenders as synchronous, while in fact they maybe didn't reach this state yet. To mitigate this problem we memorize current flush lsn on the primary right after change of `synchronous_standby_names` got visible and use it as an additional check for walsenders.
The walsender will be counted as truly "sync" only when write/flush/replay_lsn on it reached memorized LSN and the `application_name` is known to be a part of `synchronous_standby_names`.

The size of PR mostly related to refactoring and moving the code responsible for working with `synchronous_standby_names` and `pg_stat_replication` to the dedicated file.
And `parse_sync_standby_names()` function was mostly copied from #672.
This commit is contained in:
Alexander Kukushkin
2023-01-24 15:05:54 +01:00
committed by GitHub
parent 40d16443f9
commit 3161f31088
8 changed files with 395 additions and 161 deletions
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tests/test_postgresql.py
+2 -69
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@@ -10,7 +10,7 @@ from mock import Mock, MagicMock, PropertyMock, patch, mock_open
import patroni.psycopg as psycopg
from patroni.async_executor import CriticalTask
from patroni.dcs import Cluster, RemoteMember, SyncState
from patroni.dcs import RemoteMember
from patroni.exceptions import PostgresConnectionException, PatroniException
from patroni.postgresql import Postgresql, STATE_REJECT, STATE_NO_RESPONSE
from patroni.postgresql.bootstrap import Bootstrap
@@ -640,79 +640,12 @@ class TestPostgresql(BaseTestPostgresql):
self.p._state = 'starting'
self.assertIsNone(self.p.wait_for_startup())
@patch.object(Postgresql, 'last_operation', Mock(return_value=2))
def test_pick_sync_standby(self):
cluster = Cluster(True, None, self.leader, 0, [self.me, self.other, self.leadermem], None,
SyncState(0, self.me.name, self.leadermem.name), None, None, None)
with patch.object(Postgresql, "_cluster_info_state_get", side_effect=[
'on',
[{'application_name': self.leadermem.name, 'sync_state': 'sync', 'flush_lsn': 1},
{'application_name': self.me.name, 'sync_state': 'async', 'flush_lsn': 2},
{'application_name': self.other.name, 'sync_state': 'async', 'flush_lsn': 2}]
]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([self.leadermem.name], [self.leadermem.name]))
with patch.object(Postgresql, "_cluster_info_state_get", side_effect=[
'remote_write',
[{'application_name': self.leadermem.name, 'sync_state': 'potential', 'write_lsn': 1},
{'application_name': self.me.name, 'sync_state': 'async', 'write_lsn': 2},
{'application_name': self.other.name, 'sync_state': 'async', 'write_lsn': 2}]
]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([self.leadermem.name], []))
with patch.object(Postgresql, "_cluster_info_state_get", side_effect=[
'remote_apply',
[{'application_name': self.me.name.upper(), 'sync_state': 'async', 'replay_lsn': 2},
{'application_name': self.other.name, 'sync_state': 'async', 'replay_lsn': 1}]
]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([self.me.name], []))
with patch.object(Postgresql, "_cluster_info_state_get", side_effect=[
'remote_apply',
[{'application_name': 'missing', 'sync_state': 'sync', 'replay_lsn': 3},
{'application_name': self.me.name, 'sync_state': 'async', 'replay_lsn': 2},
{'application_name': self.other.name, 'sync_state': 'async', 'replay_lsn': 1}]
]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([self.me.name], []))
with patch.object(Postgresql, "_cluster_info_state_get", side_effect=['remote_apply', []]):
self.p._major_version = 90400
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([], []))
def test_set_sync_standby(self):
def value_in_conf():
with open(os.path.join(self.p.data_dir, 'postgresql.conf')) as f:
for line in f:
if line.startswith('synchronous_standby_names'):
return line.strip()
mock_reload = self.p.reload = Mock()
self.p.config.set_synchronous_standby(['n1'])
self.assertEqual(value_in_conf(), "synchronous_standby_names = 'n1'")
mock_reload.assert_called()
mock_reload.reset_mock()
self.p.config.set_synchronous_standby(['n1'])
mock_reload.assert_not_called()
self.assertEqual(value_in_conf(), "synchronous_standby_names = 'n1'")
self.p.config.set_synchronous_standby(['n1', 'n2'])
mock_reload.assert_called()
self.assertEqual(value_in_conf(), "synchronous_standby_names = '2 (n1,n2)'")
mock_reload.reset_mock()
self.p.config.set_synchronous_standby([])
mock_reload.assert_called()
self.assertEqual(value_in_conf(), None)
def test_get_server_parameters(self):
config = {'synchronous_mode': True, 'parameters': {'wal_level': 'hot_standby'}, 'listen': '0'}
self.p.config.get_server_parameters(config)
config['synchronous_mode_strict'] = True
self.p.config.get_server_parameters(config)
self.p.config.set_synchronous_standby('foo')
self.p.config.set_synchronous_standby_names('foo')
self.assertTrue(str(self.p.config.get_server_parameters(config)).startswith('{'))
@patch('time.sleep', Mock())