Clean up duplicate receipts when creating unique indexes

Before creating the `receipts_graph_unique_index` and
`receipts_linearized_unique_index` unique indexes, we have to clean up
any duplicate receipts that may have crept in due to
#14406.

Signed-off-by: Sean Quah <seanq@matrix.org>

synapse/storage/databases/main/receipts.py

@@ -113,24 +113,6 @@ def __init__(
             prefilled_cache=receipts_stream_prefill,
         )
 
-        self.db_pool.updates.register_background_index_update(
-            "receipts_linearized_unique_index",
-            index_name="receipts_linearized_unique_index",
-            table="receipts_linearized",
-            columns=["room_id", "receipt_type", "user_id"],
-            where_clause="thread_id IS NULL",
-            unique=True,
-        )
-
-        self.db_pool.updates.register_background_index_update(
-            "receipts_graph_unique_index",
-            index_name="receipts_graph_unique_index",
-            table="receipts_graph",
-            columns=["room_id", "receipt_type", "user_id"],
-            where_clause="thread_id IS NULL",
-            unique=True,
-        )
-
     def get_max_receipt_stream_id(self) -> int:
         """Get the current max stream ID for receipts stream"""
         return self._receipts_id_gen.get_current_token()
@@ -864,6 +846,8 @@ def _insert_graph_receipt_txn(
 
 class ReceiptsBackgroundUpdateStore(SQLBaseStore):
     POPULATE_RECEIPT_EVENT_STREAM_ORDERING = "populate_event_stream_ordering"
+    RECEIPTS_LINEARIZED_UNIQUE_INDEX_UPDATE_NAME = "receipts_linearized_unique_index"
+    RECEIPTS_GRAPH_UNIQUE_INDEX_UPDATE_NAME = "receipts_graph_unique_index"
 
     def __init__(
         self,
@@ -877,6 +861,14 @@ def __init__(
             self.POPULATE_RECEIPT_EVENT_STREAM_ORDERING,
             self._populate_receipt_event_stream_ordering,
         )
+        self.db_pool.updates.register_background_update_handler(
+            self.RECEIPTS_LINEARIZED_UNIQUE_INDEX_UPDATE_NAME,
+            self._background_receipts_linearized_unique_index,
+        )
+        self.db_pool.updates.register_background_update_handler(
+            self.RECEIPTS_GRAPH_UNIQUE_INDEX_UPDATE_NAME,
+            self._background_receipts_graph_unique_index,
+        )
 
     async def _populate_receipt_event_stream_ordering(
         self, progress: JsonDict, batch_size: int
@@ -932,6 +924,86 @@ def _populate_receipt_event_stream_ordering_txn(
 
         return batch_size
 
+    async def _background_receipts_unique_index(
+        self, update_name: str, index_name: str, table: str
+    ) -> int:
+        """Adds a unique index on `(room_id, receipt_type, user_id)` to the given
+        receipts table, for non-thread receipts.
+        """
+        def _receipts_unique_index_txn(txn: LoggingTransaction) -> None:
+            # Identify any duplicate receipts arising from
+            # https://github.com/matrix-org/synapse/issues/14406.
+            # We expect the following query to use the per-thread receipt index and take
+            # less than a minute.
+            sql = f"""
+                SELECT room_id, receipt_type, user_id FROM {table}
+                WHERE thread_id IS NULL
+                GROUP BY room_id, receipt_type, user_id
+                HAVING COUNT(*) > 1
+            """
+            txn.execute(sql)
+            duplicate_keys = cast(List[Tuple[str, str, str]], list(txn))
+
+            # Then remove all duplicate receipts.
+            # We could be clever and try to keep the latest receipt out of every set of
+            # duplicates, but it's far simpler to remove them all.
+            for room_id, receipt_type, user_id in duplicate_keys:
+                sql = f"""
+                    DELETE FROM {table}
+                    WHERE
+                        room_id = ? AND
+                        receipt_type = ? AND
+                        user_id = ? AND
+                        thread_id IS NULL
+                """
+                txn.execute(sql, (room_id, receipt_type, user_id))
+
+            # Now that the duplicates are gone, we can create the index.
+            concurrently = (
+                "CONCURRENTLY"
+                if isinstance(self.database_engine, PostgresEngine)
+                else ""
+            )
+            sql = f"""
+                CREATE UNIQUE INDEX {concurrently} {index_name}
+                ON {table}(room_id, receipt_type, user_id)
+                WHERE thread_id IS NULL
+            """
+            txn.execute(sql)
+
+        await self.db_pool.runInteraction(
+            update_name,
+            _receipts_unique_index_txn,
+        )
+
+        await self.db_pool.updates._end_background_update(update_name)
+
+        return 1
+
+    async def _background_receipts_linearized_unique_index(
+        self, progress: dict, batch_size: int
+    ) -> int:
+        """Adds a unique index on `(room_id, receipt_type, user_id)` to
+        `receipts_linearized`, for non-thread receipts.
+        """
+        return await self._background_receipts_unique_index(
+            self.RECEIPTS_LINEARIZED_UNIQUE_INDEX_UPDATE_NAME,
+            "receipts_linearized_unique_index",
+            "receipts_linearized",
+        )
+
+    async def _background_receipts_graph_unique_index(
+        self, progress: dict, batch_size: int
+    ) -> int:
+        """Adds a unique index on `(room_id, receipt_type, user_id)` to
+        `receipts_graph`, for non-thread receipts.
+        """
+        return await self._background_receipts_unique_index(
+            self.RECEIPTS_GRAPH_UNIQUE_INDEX_UPDATE_NAME,
+            "receipts_graph_unique_index",
+            "receipts_graph",
+        )
+
 
 class ReceiptsStore(ReceiptsWorkerStore, ReceiptsBackgroundUpdateStore):
     pass

tests/storage/databases/main/test_receipts.py

@@ -0,0 +1,169 @@
+# Copyright 2022 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the 'License');
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an 'AS IS' BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import Any, Dict
+
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.rest import admin
+from synapse.rest.client import login, room
+from synapse.server import HomeServer
+from synapse.storage.database import LoggingTransaction
+from synapse.util import Clock
+
+from tests.unittest import HomeserverTestCase
+
+
+class ReceiptsBackgroundUpdateStoreTestCase(HomeserverTestCase):
+
+    servlets = [
+        admin.register_servlets,
+        room.register_servlets,
+        login.register_servlets,
+    ]
+
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer):
+        self.store = hs.get_datastores().main
+        self.user_id = self.register_user("foo", "pass")
+        self.token = self.login("foo", "pass")
+        self.room_id = self.helper.create_room_as(self.user_id, tok=self.token)
+        self.other_room_id = self.helper.create_room_as(self.user_id, tok=self.token)
+
+    def _test_background_receipts_unique_index(
+        self,
+        update_name: str,
+        index_name: str,
+        table: str,
+        values: Dict[str, Any],
+    ):
+        """Test that the background update to uniqueify non-thread receipts in
+        the given receipts table works properly.
+        """
+        # First, undo the background update.
+        def drop_receipts_unique_index(txn: LoggingTransaction) -> None:
+            txn.execute(f"DROP INDEX IF EXISTS {index_name}")
+
+        self.get_success(
+            self.store.db_pool.runInteraction(
+                "drop_receipts_unique_index",
+                drop_receipts_unique_index,
+            )
+        )
+
+        # Add duplicate receipts for `room_id`.
+        for _ in range(2):
+            self.get_success(
+                self.store.db_pool.simple_insert(
+                    table,
+                    {
+                        "room_id": self.room_id,
+                        "receipt_type": "m.read",
+                        "user_id": self.user_id,
+                        "thread_id": None,
+                        "data": "{}",
+                        **values,
+                    },
+                )
+            )
+
+        # Add a unique receipt for `other_room_id`.
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                table,
+                {
+                    "room_id": self.other_room_id,
+                    "receipt_type": "m.read",
+                    "user_id": self.user_id,
+                    "thread_id": None,
+                    "data": "{}",
+                    **values,
+                },
+            )
+        )
+
+        # Insert and run the background update.
+        self.get_success(
+            self.store.db_pool.simple_insert(
+                "background_updates",
+                {
+                    "update_name": update_name,
+                    "progress_json": "{}",
+                },
+            )
+        )
+
+        self.store.db_pool.updates._all_done = False
+
+        self.wait_for_background_updates()
+
+        # Check that the background task deleted the duplicate receipts.
+        res = self.get_success(
+            self.store.db_pool.simple_select_onecol(
+                table=table,
+                keyvalues={
+                    "room_id": self.room_id,
+                    "receipt_type": "m.read",
+                    "user_id": self.user_id,
+                    # `simple_select_onecol` does not support NULL filters,
+                    # so skip the filter on `thread_id`.
+                },
+                retcol="room_id",
+                desc="get_receipt",
+            )
+        )
+        self.assertEqual(0, len(res))
+
+        # Check that the background task did not delete the unique receipts.
+        res = self.get_success(
+            self.store.db_pool.simple_select_onecol(
+                table=table,
+                keyvalues={
+                    "room_id": self.other_room_id,
+                    "receipt_type": "m.read",
+                    "user_id": self.user_id,
+                    # `simple_select_onecol` does not support NULL filters,
+                    # so skip the filter on `thread_id`.
+                },
+                retcol="room_id",
+                desc="get_receipt",
+            )
+        )
+        self.assertEqual(1, len(res))
+
+    def test_background_receipts_linearized_unique_index(self):
+        """Test that the background update to uniqueify non-thread receipts in
+        `receipts_linearized` works properly.
+        """
+        self._test_background_receipts_unique_index(
+            "receipts_linearized_unique_index",
+            "receipts_linearized_unique_index",
+            "receipts_linearized",
+            {
+                "stream_id": 5,
+                "event_id": "$some_event",
+            },
+        )
+
+    def test_background_receipts_graph_unique_index(self):
+        """Test that the background update to uniqueify non-thread receipts in
+        `receipts_graph` works properly.
+        """
+        self._test_background_receipts_unique_index(
+            "receipts_graph_unique_index",
+            "receipts_graph_unique_index",
+            "receipts_graph",
+            {
+                "event_ids": '["$some_event"]',
+            },
+        )