Handle half-created indices in receipts index background update (#14650)

When Synapse is terminated while running the background update to create
the `receipts_graph` or `receipts_linearized` indexes, the indexes may
be successfully created (or marked as invalid on postgres) while the
background update remains unfinished. When Synapse next starts up, the
background update will fail because the index already exists, or exists
but is invalid on postgres.

Use the existing code to create indices in background updates, since it
handles these edge cases.

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

1 files changed, 12 insertions, 39 deletions

diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index a580e4bdda..e06725f69c 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -924,39 +924,6 @@ class ReceiptsBackgroundUpdateStore(SQLBaseStore):
 
         return batch_size
 
-    async def _create_receipts_index(self, index_name: str, table: str) -> None:
-        """Adds a unique index on `(room_id, receipt_type, user_id)` to the given
-        receipts table, for non-thread receipts."""
-
-        def _create_index(conn: LoggingDatabaseConnection) -> None:
-            conn.rollback()
-
-            # we have to set autocommit, because postgres refuses to
-            # CREATE INDEX CONCURRENTLY without it.
-            if isinstance(self.database_engine, PostgresEngine):
-                conn.set_session(autocommit=True)
-
-            try:
-                c = conn.cursor()
-
-                # 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
-                """
-                c.execute(sql)
-            finally:
-                if isinstance(self.database_engine, PostgresEngine):
-                    conn.set_session(autocommit=False)
-
-        await self.db_pool.runWithConnection(_create_index)
-
     async def _background_receipts_linearized_unique_index(
         self, progress: dict, batch_size: int
     ) -> int:
@@ -999,9 +966,12 @@ class ReceiptsBackgroundUpdateStore(SQLBaseStore):
             _remote_duplicate_receipts_txn,
         )
 
-        await self._create_receipts_index(
-            "receipts_linearized_unique_index",
-            "receipts_linearized",
+        await self.db_pool.updates.create_index_in_background(
+            index_name="receipts_linearized_unique_index",
+            table="receipts_linearized",
+            columns=["room_id", "receipt_type", "user_id"],
+            where_clause="thread_id IS NULL",
+            unique=True,
         )
 
         await self.db_pool.updates._end_background_update(
@@ -1050,9 +1020,12 @@ class ReceiptsBackgroundUpdateStore(SQLBaseStore):
             _remote_duplicate_receipts_txn,
         )
 
-        await self._create_receipts_index(
-            "receipts_graph_unique_index",
-            "receipts_graph",
+        await self.db_pool.updates.create_index_in_background(
+            index_name="receipts_graph_unique_index",
+            table="receipts_graph",
+            columns=["room_id", "receipt_type", "user_id"],
+            where_clause="thread_id IS NULL",
+            unique=True,
         )
 
         await self.db_pool.updates._end_background_update(