Remove connection parameter caching in Pool

Currently, `asyncpt.Pool` will cache various aspects of the connection,
like the selected host and connection parameters in an attempt to make
subsequent connection attempts somewhat faster.  This behavior is
dubious because server host availability and role may change, such as
when a primary becomes a standby and vice-versa or when a host becomes
unavailable permanently, but another host from the DSN can be picked up.
Just remove it.

asyncpg/pool.py

@@ -311,7 +311,6 @@ class Pool:
     __slots__ = (
         '_queue', '_loop', '_minsize', '_maxsize',
         '_init', '_connect_args', '_connect_kwargs',
-        '_working_addr', '_working_config', '_working_params',
         '_holders', '_initialized', '_initializing', '_closing',
         '_closed', '_connection_class', '_record_class', '_generation',
         '_setup', '_max_queries', '_max_inactive_connection_lifetime'
@@ -377,10 +376,6 @@ def __init__(self, *connect_args,
         self._initializing = False
         self._queue = None
 
-        self._working_addr = None
-        self._working_config = None
-        self._working_params = None
-
         self._connection_class = connection_class
         self._record_class = record_class
 
@@ -430,9 +425,8 @@ async def _initialize(self):
             # first few connections in the queue, therefore we want to walk
             # `self._holders` in reverse.
 
-            # Connect the first connection holder in the queue so that it
-            # can record `_working_addr` and `_working_opts`, which will
-            # speed up successive connection attempts.
+            # Connect the first connection holder in the queue so that
+            # any connection issues are visible early.
             first_ch = self._holders[-1]  # type: PoolConnectionHolder
             await first_ch.connect()
 
@@ -504,36 +498,15 @@ def set_connect_args(self, dsn=None, **connect_kwargs):
 
         self._connect_args = [dsn]
         self._connect_kwargs = connect_kwargs
-        self._working_addr = None
-        self._working_config = None
-        self._working_params = None
 
     async def _get_new_connection(self):
-        if self._working_addr is None:
-            # First connection attempt on this pool.
-            con = await connection.connect(
-                *self._connect_args,
-                loop=self._loop,
-                connection_class=self._connection_class,
-                record_class=self._record_class,
-                **self._connect_kwargs)
-
-            self._working_addr = con._addr
-            self._working_config = con._config
-            self._working_params = con._params
-
-        else:
-            # We've connected before and have a resolved address,
-            # and parsed options and config.
-            con = await connect_utils._connect_addr(
-                loop=self._loop,
-                addr=self._working_addr,
-                timeout=self._working_params.connect_timeout,
-                config=self._working_config,
-                params=self._working_params,
-                connection_class=self._connection_class,
-                record_class=self._record_class,
-            )
+        con = await connection.connect(
+            *self._connect_args,
+            loop=self._loop,
+            connection_class=self._connection_class,
+            record_class=self._record_class,
+            **self._connect_kwargs,
+        )
 
         if self._init is not None:
             try:

tests/test_pool.py

@@ -8,6 +8,7 @@
 import asyncio
 import inspect
 import os
+import pathlib
 import platform
 import random
 import textwrap
@@ -18,6 +19,7 @@
 from asyncpg import _testbase as tb
 from asyncpg import connection as pg_connection
 from asyncpg import pool as pg_pool
+from asyncpg import cluster as pg_cluster
 
 _system = platform.uname().system
 
@@ -969,6 +971,70 @@ async def worker():
         await pool.release(conn)
 
 
+@unittest.skipIf(os.environ.get('PGHOST'), 'unmanaged cluster')
+class TestPoolReconnectWithTargetSessionAttrs(tb.ClusterTestCase):
+
+    @classmethod
+    def setup_cluster(cls):
+        cls.cluster = cls.new_cluster(pg_cluster.TempCluster)
+        cls.start_cluster(cls.cluster)
+
+    async def simulate_cluster_recovery_mode(self):
+        port = self.cluster.get_connection_spec()['port']
+        await self.loop.run_in_executor(
+            None,
+            lambda: self.cluster.stop()
+        )
+
+        # Simulate recovery mode
+        (pathlib.Path(self.cluster._data_dir) / 'standby.signal').touch()
+
+        await self.loop.run_in_executor(
+            None,
+            lambda: self.cluster.start(
+                port=port,
+                server_settings=self.get_server_settings(),
+            )
+        )
+
+    async def test_full_reconnect_on_node_change_role(self):
+        if self.cluster.get_pg_version() < (12, 0):
+            self.skipTest("PostgreSQL < 12 cannot support standby.signal")
+            return
+
+        pool = await self.create_pool(
+            min_size=1,
+            max_size=1,
+            target_session_attrs='primary'
+        )
+
+        # Force a new connection to be created
+        await pool.fetchval('SELECT 1')
+
+        await self.simulate_cluster_recovery_mode()
+
+        # current pool connection info cache is expired,
+        # but we don't know it yet
+        with self.assertRaises(asyncpg.TargetServerAttributeNotMatched) as cm:
+            await pool.execute('SELECT 1')
+
+        self.assertEqual(
+            cm.exception.args[0],
+            "None of the hosts match the target attribute requirement "
+            "<SessionAttribute.primary: 'primary'>"
+        )
+
+        # force reconnect
+        with self.assertRaises(asyncpg.TargetServerAttributeNotMatched) as cm:
+            await pool.execute('SELECT 1')
+
+        self.assertEqual(
+            cm.exception.args[0],
+            "None of the hosts match the target attribute requirement "
+            "<SessionAttribute.primary: 'primary'>"
+        )
+
+
 @unittest.skipIf(os.environ.get('PGHOST'), 'using remote cluster for testing')
 class TestHotStandby(tb.HotStandbyTestCase):
     def create_pool(self, **kwargs):