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Multi Sync Standby Support (#1594)

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The new parameter `synchronous_node_count` is used by Patroni to manage number of synchronous standby databases. It is set to 1 by default. It has no effect when synchronous_mode is set to off. When enabled, Patroni manages precise number of synchronous standby databases based on parameter synchronous_node_count and adjusts the state in DCS & synchronous_standby_names as members join and leave.

This functionality can be further extended to support Priority (FIRST n) based synchronous replication & Quorum (ANY n) based synchronous replication in future.
This commit is contained in:
ksarabu1
2020-08-14 11:51:07 +02:00
committed by GitHub
parent fce1955218
commit 1ab709c5f0
14 changed files with 163 additions and 95 deletions
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tests/test_postgresql.py
+33 -26
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@@ -595,36 +595,43 @@ class TestPostgresql(BaseTestPostgresql):
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)
mock_cursor = Mock()
mock_cursor.fetchone.return_value = ('remote_apply',)
with patch.object(Postgresql, "query", return_value=[
(self.leadermem.name, 'streaming', 'sync'),
(self.me.name, 'streaming', 'async'),
(self.other.name, 'streaming', 'async'),
with patch.object(Postgresql, "query", side_effect=[
mock_cursor,
[(self.leadermem.name, 'streaming', 'sync'),
(self.me.name, 'streaming', 'async'),
(self.other.name, 'streaming', 'async')]
]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), (self.leadermem.name, True))
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([self.leadermem.name], [self.leadermem.name]))
with patch.object(Postgresql, "query", return_value=[
(self.me.name, 'streaming', 'async'),
(self.leadermem.name, 'streaming', 'potential'),
(self.other.name, 'streaming', 'async'),
with patch.object(Postgresql, "query", side_effect=[
mock_cursor,
[(self.leadermem.name, 'streaming', 'potential'),
(self.me.name, 'streaming', 'async'),
(self.other.name, 'streaming', 'async')]
]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), (self.leadermem.name, False))
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([self.leadermem.name], []))
with patch.object(Postgresql, "query", return_value=[
(self.me.name, 'streaming', 'async'),
(self.other.name, 'streaming', 'async'),
with patch.object(Postgresql, "query", side_effect=[
mock_cursor,
[(self.me.name, 'streaming', 'async'),
(self.other.name, 'streaming', 'async')]
]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), (self.me.name, False))
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([self.me.name], []))
with patch.object(Postgresql, "query", return_value=[
('missing', 'streaming', 'sync'),
(self.me.name, 'streaming', 'async'),
(self.other.name, 'streaming', 'async'),
with patch.object(Postgresql, "query", side_effect=[
mock_cursor,
[('missing', 'streaming', 'sync'),
(self.me.name, 'streaming', 'async'),
(self.other.name, 'streaming', 'async')]
]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), (self.me.name, False))
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([self.me.name], []))
with patch.object(Postgresql, "query", return_value=[]):
self.assertEqual(self.p.pick_synchronous_standby(cluster), (None, False))
with patch.object(Postgresql, "query", side_effect=[mock_cursor, []]):
self.p._major_version = 90400
self.assertEqual(self.p.pick_synchronous_standby(cluster), ([], []))
def test_set_sync_standby(self):
def value_in_conf():
@@ -634,21 +641,21 @@ class TestPostgresql(BaseTestPostgresql):
return line.strip()
mock_reload = self.p.reload = Mock()
self.p.config.set_synchronous_standby('n1')
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')
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('n2')
self.p.config.set_synchronous_standby(['n1', 'n2'])
mock_reload.assert_called()
self.assertEqual(value_in_conf(), "synchronous_standby_names = 'n2'")
self.assertEqual(value_in_conf(), "synchronous_standby_names = '2 (n1,n2)'")
mock_reload.reset_mock()
self.p.config.set_synchronous_standby(None)
self.p.config.set_synchronous_standby([])
mock_reload.assert_called()
self.assertEqual(value_in_conf(), None)