Revert "extend test_change_pageserver for failure case, rework changing pageserver (#5693)"

This reverts commit b989ad1922.

test_runner/regress/test_change_pageserver.py

@@ -1,13 +1,9 @@
-import asyncio
-
 from fixtures.log_helper import log
 from fixtures.neon_fixtures import NeonEnvBuilder
 from fixtures.remote_storage import RemoteStorageKind
 
 
 def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
-    num_connections = 3
-
     neon_env_builder.num_pageservers = 2
     neon_env_builder.enable_pageserver_remote_storage(
         remote_storage_kind=RemoteStorageKind.MOCK_S3,
@@ -20,24 +16,15 @@ def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
     alt_pageserver_id = env.pageservers[1].id
     env.pageservers[1].tenant_attach(env.initial_tenant)
 
-    pg_conns = [endpoint.connect() for i in range(num_connections)]
-    curs = [pg_conn.cursor() for pg_conn in pg_conns]
-
-    def execute(statement: str):
-        for cur in curs:
-            cur.execute(statement)
-
-    def fetchone():
-        results = [cur.fetchone() for cur in curs]
-        assert all(result == results[0] for result in results)
-        return results[0]
+    pg_conn = endpoint.connect()
+    cur = pg_conn.cursor()
 
     # Create table, and insert some rows. Make it big enough that it doesn't fit in
     # shared_buffers, otherwise the SELECT after restart will just return answer
     # from shared_buffers without hitting the page server, which defeats the point
     # of this test.
-    curs[0].execute("CREATE TABLE foo (t text)")
-    curs[0].execute(
+    cur.execute("CREATE TABLE foo (t text)")
+    cur.execute(
         """
         INSERT INTO foo
             SELECT 'long string to consume some space' || g
@@ -46,25 +33,25 @@ def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
     )
 
     # Verify that the table is larger than shared_buffers
-    curs[0].execute(
+    cur.execute(
         """
         select setting::int * pg_size_bytes(unit) as shared_buffers, pg_relation_size('foo') as tbl_size
         from pg_settings where name = 'shared_buffers'
         """
     )
-    row = curs[0].fetchone()
+    row = cur.fetchone()
     assert row is not None
     log.info(f"shared_buffers is {row[0]}, table size {row[1]}")
     assert int(row[0]) < int(row[1])
 
-    execute("SELECT count(*) FROM foo")
-    assert fetchone() == (100000,)
+    cur.execute("SELECT count(*) FROM foo")
+    assert cur.fetchone() == (100000,)
 
     endpoint.reconfigure(pageserver_id=alt_pageserver_id)
 
     # Verify that the neon.pageserver_connstring GUC is set to the correct thing
-    execute("SELECT setting FROM pg_settings WHERE name='neon.pageserver_connstring'")
-    connstring = fetchone()
+    cur.execute("SELECT setting FROM pg_settings WHERE name='neon.pageserver_connstring'")
+    connstring = cur.fetchone()
     assert connstring is not None
     expected_connstring = f"postgresql://no_user:@localhost:{env.pageservers[1].service_port.pg}"
     assert expected_connstring == expected_connstring
@@ -73,45 +60,5 @@ def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
         0
     ].stop()  # Stop the old pageserver just to make sure we're reading from the new one
 
-    execute("SELECT count(*) FROM foo")
-    assert fetchone() == (100000,)
-
-    # Try failing back, and this time we will stop the current pageserver before reconfiguring
-    # the endpoint.  Whereas the previous reconfiguration was like a healthy migration, this
-    # is more like what happens in an unexpected  pageserver failure.
-    env.pageservers[0].start()
-    env.pageservers[1].stop()
-
-    endpoint.reconfigure(pageserver_id=env.pageservers[0].id)
-
-    execute("SELECT count(*) FROM foo")
-    assert fetchone() == (100000,)
-
-    env.pageservers[0].stop()
-    env.pageservers[1].start()
-
-    # Test a (former) bug where a child process spins without updating its connection string
-    # by executing a query separately. This query will hang until we issue the reconfigure.
-    async def reconfigure_async():
-        await asyncio.sleep(
-            1
-        )  # Sleep for 1 second just to make sure we actually started our count(*) query
-        endpoint.reconfigure(pageserver_id=env.pageservers[1].id)
-
-    def execute_count():
-        execute("SELECT count(*) FROM FOO")
-
-    async def execute_and_reconfigure():
-        task_exec = asyncio.to_thread(execute_count)
-        task_reconfig = asyncio.create_task(reconfigure_async())
-        await asyncio.gather(
-            task_exec,
-            task_reconfig,
-        )
-
-    asyncio.run(execute_and_reconfigure())
-    assert fetchone() == (100000,)
-
-    # One final check that nothing hangs
-    execute("SELECT count(*) FROM foo")
-    assert fetchone() == (100000,)
+    cur.execute("SELECT count(*) FROM foo")
+    assert cur.fetchone() == (100000,)