Permanent physical slots on standby nodes (#2852)

Create permanent physical replication slots on standby nodes and use `pg_replication_slot_advance()` function to move them forward.

The `restart_lsn` is advanced based on values stored in the `/status` key by the primary node.

When slot is created on a replica it could be ahead the same slot on the primary and therefore there is some period of time when it doesn't protect WAL files from being recycled.

features/ignored_slots.feature

@@ -25,10 +25,10 @@ Feature: ignored slots
     # but Patroni can actually end up dropping them almost immediately, so it's helpful
     # to verify they exist before we begin testing whether they persist through failover
     # cycles.
-    Then postgres1 has a logical replication slot named unmanaged_slot_0 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_1 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_2 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_3 with the test_decoding plugin
+    Then postgres1 has a logical replication slot named unmanaged_slot_0 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_1 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_2 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_3 with the test_decoding plugin after 2 seconds
 
     When I start postgres0
     Then "members/postgres0" key in DCS has role=replica after 10 seconds
@@ -46,16 +46,16 @@ Feature: ignored slots
     And "members/postgres1" key in DCS has role=replica after 10 seconds
     # give Patroni time to sync replication slots
     And I sleep for 2 seconds
-    And postgres1 has a logical replication slot named unmanaged_slot_0 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_1 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_2 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_3 with the test_decoding plugin
+    And postgres1 has a logical replication slot named unmanaged_slot_0 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_1 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_2 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_3 with the test_decoding plugin after 2 seconds
     And postgres1 does not have a logical replication slot named dummy_slot
 
     # 3. After a failover the server (now a primary) still has the slot.
     When I shut down postgres0
     Then "members/postgres1" key in DCS has role=master after 10 seconds
-    And postgres1 has a logical replication slot named unmanaged_slot_0 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_1 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_2 with the test_decoding plugin
-    And postgres1 has a logical replication slot named unmanaged_slot_3 with the test_decoding plugin
+    And postgres1 has a logical replication slot named unmanaged_slot_0 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_1 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_2 with the test_decoding plugin after 2 seconds
+    And postgres1 has a logical replication slot named unmanaged_slot_3 with the test_decoding plugin after 2 seconds

features/permanent_slots.feature

@@ -0,0 +1,34 @@
+Feature: permanent slots
+  Scenario: check that physical permanent slots are created
+    Given I start postgres0
+    Then postgres0 is a leader after 10 seconds
+    And there is a non empty initialize key in DCS after 15 seconds
+    When I issue a PATCH request to http://127.0.0.1:8008/config with {"slots": {"test_physical": {"type": "physical"}}, "postgresql": {"parameters": {"wal_level": "logical"}}}
+    Then I receive a response code 200
+    And Response on GET http://127.0.0.1:8008/config contains slots after 10 seconds
+    Then postgres0 has a physical replication slot named test_physical after 10 seconds
+    And I start postgres1
+
+  @slot-advance
+  Scenario: check that logical permanent slots are created
+    Given I run patronictl.py restart batman postgres0 --force
+    And I issue a PATCH request to http://127.0.0.1:8008/config with {"slots": {"test_logical": {"type": "logical", "database": "postgres", "plugin": "test_decoding"}}}
+    Then postgres0 has a logical replication slot named test_logical with the test_decoding plugin after 10 seconds
+
+  @slot-advance
+  Scenario: check that permanent slots are created on the replica
+    Given postgres1 has a logical replication slot named test_logical with the test_decoding plugin after 10 seconds
+    Then Logical slot test_logical is in sync between postgres0 and postgres1 after 10 seconds
+    And postgres1 has a physical replication slot named test_physical after 2 seconds
+
+  @slot-advance
+  Scenario: check that permanent slots are advanced on the replica
+    Given I add the table replicate_me to postgres0
+    And I get all changes from physical slot test_physical on postgres0
+    When I get all changes from logical slot test_logical on postgres0
+    Then Logical slot test_logical is in sync between postgres0 and postgres1 after 10 seconds
+    And Physical slot test_physical is in sync between postgres0 and postgres1 after 10 seconds
+
+  Scenario: check permanent physical replication slot after failover
+    Given I shut down postgres0
+    Then postgres1 has a physical replication slot named test_physical after 10 seconds

features/standby_cluster.feature

@@ -22,9 +22,6 @@ Feature: standby cluster
   Scenario: check permanent logical slots are synced to the replica
     Given I run patronictl.py restart batman postgres1 --force
     Then Logical slot test_logical is in sync between postgres0 and postgres1 after 10 seconds
-    When I add the table replicate_me to postgres1
-    And I get all changes from logical slot test_logical on postgres1
-    Then Logical slot test_logical is in sync between postgres0 and postgres1 after 10 seconds
 
   Scenario: Detach exiting node from the cluster
     When I shut down postgres1

features/steps/slots.py

@@ -15,17 +15,25 @@ def create_logical_replication_slot(context, slot_name, pg_name, plugin):
         assert False, "Error creating slot {0} on {1} with plugin {2}".format(slot_name, pg_name, plugin)
 
 
-@then('{pg_name:w} has a logical replication slot named {slot_name} with the {plugin:w} plugin')
-def has_logical_replication_slot(context, pg_name, slot_name, plugin):
-    try:
-        row = context.pctl.query(pg_name, ("SELECT slot_type, plugin FROM pg_replication_slots"
-                                           " WHERE slot_name = '{0}'").format(slot_name)).fetchone()
-        assert row, "Couldn't find replication slot named {0}".format(slot_name)
-        assert row[0] == "logical", "Found replication slot named {0} but wasn't a logical slot".format(slot_name)
-        assert row[1] == plugin, ("Found replication slot named {0} but was using plugin "
-                                  "{1} rather than {2}").format(slot_name, row[1], plugin)
-    except pg.Error:
-        assert False, "Error looking for slot {0} on {1} with plugin {2}".format(slot_name, pg_name, plugin)
+@step('{pg_name:w} has a logical replication slot named {slot_name}'
+      ' with the {plugin:w} plugin after {time_limit:d} seconds')
+@then('{pg_name:w} has a logical replication slot named {slot_name}'
+      ' with the {plugin:w} plugin after {time_limit:d} seconds')
+def has_logical_replication_slot(context, pg_name, slot_name, plugin, time_limit):
+    time_limit *= context.timeout_multiplier
+    max_time = time.time() + int(time_limit)
+    while time.time() < max_time:
+        try:
+            row = context.pctl.query(pg_name, ("SELECT slot_type, plugin FROM pg_replication_slots"
+                                               f" WHERE slot_name = '{slot_name}'")).fetchone()
+            if row:
+                assert row[0] == "logical", f"Replication slot {slot_name} isn't a logical but {row[0]}"
+                assert row[1] == plugin, f"Replication slot {slot_name} using plugin {row[1]} rather than {plugin}"
+                return
+        except Exception:
+            pass
+        time.sleep(1)
+    assert False, f"Error looking for slot {slot_name} on {pg_name} with plugin {plugin}"
 
 
 @then('{pg_name:w} does not have a logical replication slot named {slot_name}')
@@ -38,13 +46,14 @@ def does_not_have_logical_replication_slot(context, pg_name, slot_name):
         assert False, "Error looking for slot {0} on {1}".format(slot_name, pg_name)
 
 
-@step('Logical slot {slot_name:w} is in sync between {pg_name1:w} and {pg_name2:w} after {time_limit:d} seconds')
-def logical_slots_in_sync(context, slot_name, pg_name1, pg_name2, time_limit):
+@step('{slot_type:w} slot {slot_name:w} is in sync between {pg_name1:w} and {pg_name2:w} after {time_limit:d} seconds')
+def slots_in_sync(context, slot_type, slot_name, pg_name1, pg_name2, time_limit):
     time_limit *= context.timeout_multiplier
     max_time = time.time() + int(time_limit)
+    column = 'confirmed_flush_lsn' if slot_type.lower() == 'logical' else 'restart_lsn'
+    query = f"SELECT {column} FROM pg_replication_slots WHERE slot_name = '{slot_name}'"
     while time.time() < max_time:
         try:
-            query = "SELECT confirmed_flush_lsn FROM pg_replication_slots WHERE slot_name = '{0}'".format(slot_name)
             slot1 = context.pctl.query(pg_name1, query).fetchone()
             slot2 = context.pctl.query(pg_name2, query).fetchone()
             if slot1[0] == slot2[0]:
@@ -52,9 +61,31 @@ def logical_slots_in_sync(context, slot_name, pg_name1, pg_name2, time_limit):
         except Exception:
             pass
         time.sleep(1)
-    assert False, "Logical slot {0} is not in sync between {1} and {2}".format(slot_name, pg_name1, pg_name2)
+    assert False, \
+        f"{slot_type} slot {slot_name} is not in sync between {pg_name1} and {pg_name2} after {time_limit} seconds"
 
 
 @step('I get all changes from logical slot {slot_name:w} on {pg_name:w}')
 def logical_slot_get_changes(context, slot_name, pg_name):
     context.pctl.query(pg_name, "SELECT * FROM pg_logical_slot_get_changes('{0}', NULL, NULL)".format(slot_name))
+
+
+@step('I get all changes from physical slot {slot_name:w} on {pg_name:w}')
+def physical_slot_get_changes(context, slot_name, pg_name):
+    context.pctl.query(pg_name, f"SELECT * FROM pg_replication_slot_advance('{slot_name}', pg_current_wal_lsn())")
+
+
+@step('{pg_name:w} has a physical replication slot named {slot_name} after {time_limit:d} seconds')
+def has_physical_replication_slot(context, pg_name, slot_name, time_limit):
+    time_limit *= context.timeout_multiplier
+    max_time = time.time() + int(time_limit)
+    query = f"SELECT * FROM pg_catalog.pg_replication_slots WHERE slot_type = 'physical' AND slot_name = '{slot_name}'"
+    while time.time() < max_time:
+        try:
+            row = context.pctl.query(pg_name, query).fetchone()
+            if row:
+                return
+        except Exception:
+            pass
+        time.sleep(1)
+    assert False, f"Physical slot {slot_name} doesn't exist after {time_limit} seconds"