mirror of
https://github.com/outbackdingo/patroni.git
synced 2026-08-25 14:53:37 +00:00
Alexander KukushkinandGitHub
04b9fb9dd4
Patroni is caching the cluster view in the DCS object because not all operations require the most up-to-date values. The cached version is valid for TTL seconds. So far it worked quite well, the only known problem was that the `last_leader_operation` for some DCS implementations was not very up-to-date: * Etcd: since the `/optime/leader` key is updated right after the `/leader` key, usually all replicas get the value from the previous HA loop. Therefore the value is somewhere between `loop_wait` and `loop_wait*2` old. We improve it by using the 10ms artificial sleep after receiving watch notification from `compareAndSwap` operation on the leader key. It usually gives enough time for the primary to update the `/optime/leader`. On average that makes the cached version `loop_wait/2` old. * ZooKeeper: Patroni itself is not so much interested in most up-to-date values of member and leader/optime ZNodes. In case of the leader race it just reads everything from ZooKeeper, but during normal operation it is relying on cache. In order to see the recent value on replicas they are doing watch on the `leader/optime` Znode and will re-read it after it was updated by the primary. On average that makes the cached version `loop_wait/2` old. * Kubernetes: last_leader_operation is stored in the same object as the leader key itself and therefore update is atomic and we always see the latest version. That makes the cached version `loop_wait/2` old on avg. * Consul: HA loops on the primary and replicas are not synchronized, therefore at the moment when we read the cluster state from the Consul KV we see the last_leader_operation value that is between 0 and loop_wait old. On average that makes the cached version `loop_wait` old. Unfortunately we can't make it much better without performing periodic updates from Consul, which might have negative side effects. Since the `optime/leader` is only updated at most once per HA loop cycle, the value stored in the DCS is usually `loop_wait/2` old on avg. For majority of DCS implementations we could promise that the cached version in Patroni will match the value in DCS most of the time, therefore there is no need to make additional requests. The only exception is Consul, but probably we could just document it, so when someone relying on last_leader_operation value to check the replication lag can correspondingly adjust thresholds. Will help to implement #1599
240 lines
9.2 KiB
Python
240 lines
9.2 KiB
Python
import select
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import six
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import unittest
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from kazoo.client import KazooState
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from kazoo.exceptions import NoNodeError, NodeExistsError
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from kazoo.handlers.threading import SequentialThreadingHandler
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from kazoo.protocol.states import ZnodeStat
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from mock import Mock, patch
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from patroni.dcs.zookeeper import Leader, PatroniSequentialThreadingHandler, ZooKeeper, ZooKeeperError
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class MockKazooClient(Mock):
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leader = False
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exists = True
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def __init__(self, *args, **kwargs):
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super(MockKazooClient, self).__init__()
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self._session_timeout = 30
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@property
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def client_id(self):
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return (-1, '')
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@staticmethod
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def retry(func, *args, **kwargs):
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return func(*args, **kwargs)
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def get(self, path, watch=None):
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if not isinstance(path, six.string_types):
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raise TypeError("Invalid type for 'path' (string expected)")
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if path == '/no_node':
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raise NoNodeError
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elif '/members/' in path:
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return (
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b'postgres://repuser:rep-pass@localhost:5434/postgres?application_name=http://127.0.0.1:8009/patroni',
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ZnodeStat(0, 0, 0, 0, 0, 0, 0, 0 if self.exists else -1, 0, 0, 0)
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)
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elif path.endswith('/optime/leader'):
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return (b'500', ZnodeStat(0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0))
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elif path.endswith('/leader'):
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if self.leader:
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return (b'foo', ZnodeStat(0, 0, 0, 0, 0, 0, 0, -1, 0, 0, 0))
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return (b'foo', ZnodeStat(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0))
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elif path.endswith('/initialize'):
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return (b'foo', ZnodeStat(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0))
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return (b'', ZnodeStat(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0))
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@staticmethod
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def get_children(path, watch=None, include_data=False):
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if not isinstance(path, six.string_types):
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raise TypeError("Invalid type for 'path' (string expected)")
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if path.startswith('/no_node'):
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raise NoNodeError
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elif path in ['/service/bla/', '/service/test/']:
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return ['initialize', 'leader', 'members', 'optime', 'failover', 'sync']
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return ['foo', 'bar', 'buzz']
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def create(self, path, value=b"", acl=None, ephemeral=False, sequence=False, makepath=False):
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if not isinstance(path, six.string_types):
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raise TypeError("Invalid type for 'path' (string expected)")
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if not isinstance(value, (six.binary_type,)):
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raise TypeError("Invalid type for 'value' (must be a byte string)")
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if b'Exception' in value:
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raise Exception
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if path.endswith('/initialize') or path == '/service/test/optime/leader':
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raise Exception
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elif b'retry' in value or (b'exists' in value and self.exists):
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raise NodeExistsError
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def create_async(self, path, value=b"", acl=None, ephemeral=False, sequence=False, makepath=False):
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return self.create(path, value, acl, ephemeral, sequence, makepath) or Mock()
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@staticmethod
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def set(path, value, version=-1):
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if not isinstance(path, six.string_types):
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raise TypeError("Invalid type for 'path' (string expected)")
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if not isinstance(value, (six.binary_type,)):
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raise TypeError("Invalid type for 'value' (must be a byte string)")
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if path == '/service/bla/optime/leader':
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raise Exception
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if path == '/service/test/members/bar' and b'retry' in value:
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return
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if path in ('/service/test/failover', '/service/test/config', '/service/test/sync'):
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if b'Exception' in value:
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raise Exception
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elif value == b'ok':
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return
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raise NoNodeError
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def set_async(self, path, value, version=-1):
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return self.set(path, value, version) or Mock()
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def delete(self, path, version=-1, recursive=False):
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if not isinstance(path, six.string_types):
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raise TypeError("Invalid type for 'path' (string expected)")
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self.exists = False
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if path == '/service/test/leader':
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self.leader = True
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raise Exception
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elif path == '/service/test/members/buzz':
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raise Exception
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elif path.endswith('/') or path.endswith('/initialize') or path == '/service/test/members/bar':
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raise NoNodeError
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def delete_async(self, path, version=-1, recursive=False):
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return self.delete(path, version, recursive) or Mock()
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class TestPatroniSequentialThreadingHandler(unittest.TestCase):
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def setUp(self):
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self.handler = PatroniSequentialThreadingHandler(10)
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@patch.object(SequentialThreadingHandler, 'create_connection', Mock())
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def test_create_connection(self):
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self.assertIsNotNone(self.handler.create_connection(()))
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self.assertIsNotNone(self.handler.create_connection((), 40))
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self.assertIsNotNone(self.handler.create_connection(timeout=40))
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@patch.object(SequentialThreadingHandler, 'select', Mock(side_effect=ValueError))
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def test_select(self):
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self.assertRaises(select.error, self.handler.select)
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class TestZooKeeper(unittest.TestCase):
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@patch('patroni.dcs.zookeeper.KazooClient', MockKazooClient)
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def setUp(self):
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self.zk = ZooKeeper({'hosts': ['localhost:2181'], 'scope': 'test',
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'name': 'foo', 'ttl': 30, 'retry_timeout': 10, 'loop_wait': 10})
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def test_session_listener(self):
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self.zk.session_listener(KazooState.SUSPENDED)
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def test_reload_config(self):
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self.zk.reload_config({'ttl': 20, 'retry_timeout': 10, 'loop_wait': 10})
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self.zk.reload_config({'ttl': 20, 'retry_timeout': 10, 'loop_wait': 5})
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def test_get_node(self):
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self.assertIsNone(self.zk.get_node('/no_node'))
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def test_get_children(self):
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self.assertListEqual(self.zk.get_children('/no_node'), [])
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def test__inner_load_cluster(self):
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self.zk._base_path = self.zk._base_path.replace('test', 'bla')
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self.zk._inner_load_cluster()
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self.zk._base_path = self.zk._base_path = '/no_node'
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self.zk._inner_load_cluster()
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def test_get_cluster(self):
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self.assertRaises(ZooKeeperError, self.zk.get_cluster)
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cluster = self.zk.get_cluster(True)
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self.assertIsInstance(cluster.leader, Leader)
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self.zk.touch_member({'foo': 'foo'})
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self.zk._name = 'bar'
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self.zk.optime_watcher(None)
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with patch.object(ZooKeeper, 'get_node', Mock(side_effect=Exception)):
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self.zk.get_cluster()
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cluster = self.zk.get_cluster()
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self.assertEqual(cluster.last_leader_operation, 500)
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def test_delete_leader(self):
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self.assertTrue(self.zk.delete_leader())
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def test_set_failover_value(self):
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self.zk.set_failover_value('')
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self.zk.set_failover_value('ok')
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self.zk.set_failover_value('Exception')
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def test_set_config_value(self):
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self.zk.set_config_value('', 1)
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self.zk.set_config_value('ok')
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self.zk.set_config_value('Exception')
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def test_initialize(self):
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self.assertFalse(self.zk.initialize())
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def test_cancel_initialization(self):
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self.zk.cancel_initialization()
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def test_touch_member(self):
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self.zk._name = 'buzz'
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self.zk.get_cluster()
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self.zk.touch_member({'new': 'new'})
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self.zk._name = 'bar'
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self.zk.touch_member({'new': 'new'})
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self.zk._name = 'na'
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self.zk._client.exists = 1
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self.zk.touch_member({'Exception': 'Exception'})
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self.zk._name = 'bar'
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self.zk.touch_member({'retry': 'retry'})
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self.zk._fetch_cluster = True
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self.zk.get_cluster()
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self.zk.touch_member({'conn_url': 'postgres://repuser:rep-pass@localhost:5434/postgres',
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'api_url': 'http://127.0.0.1:8009/patroni'})
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def test_take_leader(self):
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self.zk.take_leader()
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with patch.object(MockKazooClient, 'create', Mock(side_effect=Exception)):
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self.zk.take_leader()
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def test_update_leader(self):
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self.assertTrue(self.zk.update_leader(None))
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def test_write_leader_optime(self):
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self.zk.last_leader_operation = '0'
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self.zk.write_leader_optime('1')
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with patch.object(MockKazooClient, 'create_async', Mock()):
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self.zk.write_leader_optime('1')
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with patch.object(MockKazooClient, 'set_async', Mock()):
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self.zk.write_leader_optime('2')
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self.zk._base_path = self.zk._base_path.replace('test', 'bla')
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self.zk.write_leader_optime('3')
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def test_delete_cluster(self):
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self.assertTrue(self.zk.delete_cluster())
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def test_watch(self):
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self.zk.watch(None, 0)
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self.zk.event.isSet = Mock(return_value=True)
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self.zk._fetch_optime = False
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self.zk.watch(None, 0)
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def test__kazoo_connect(self):
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self.zk._client._retry.deadline = 1
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self.zk._orig_kazoo_connect = Mock(return_value=(0, 0))
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self.zk._kazoo_connect(None, None)
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def test_sync_state(self):
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self.zk.set_sync_state_value('')
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self.zk.set_sync_state_value('ok')
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self.zk.set_sync_state_value('Exception')
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self.zk.delete_sync_state()
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def test_set_history_value(self):
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self.zk.set_history_value('{}')
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