Merge pull request #6156 from matrix-org/erikj/postgres_any

Use Postgres ANY for selecting many values.

15 files changed, 190 insertions, 109 deletions

diff --git a/changelog.d/6156.misc b/changelog.d/6156.misc
new file mode 100644
index 0000000000..49525e9416
--- /dev/null
+++ b/changelog.d/6156.misc
@@ -0,0 +1 @@
+Use Postgres ANY for selecting many values.
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 06cc14fcd1..f5906fcd54 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -20,6 +20,7 @@ import random
 import sys
 import threading
 import time
+from typing import Iterable, Tuple
 
 from six import PY2, iteritems, iterkeys, itervalues
 from six.moves import builtins, intern, range
@@ -1163,19 +1164,18 @@ class SQLBaseStore(object):
         if not iterable:
             return []
 
-        sql = "SELECT %s FROM %s" % (", ".join(retcols), table)
-
-        clauses = []
-        values = []
-        clauses.append("%s IN (%s)" % (column, ",".join("?" for _ in iterable)))
-        values.extend(iterable)
+        clause, values = make_in_list_sql_clause(txn.database_engine, column, iterable)
+        clauses = [clause]
 
         for key, value in iteritems(keyvalues):
             clauses.append("%s = ?" % (key,))
             values.append(value)
 
-        if clauses:
-            sql = "%s WHERE %s" % (sql, " AND ".join(clauses))
+        sql = "SELECT %s FROM %s WHERE %s" % (
+            ", ".join(retcols),
+            table,
+            " AND ".join(clauses),
+        )
 
         txn.execute(sql, values)
         return cls.cursor_to_dict(txn)
@@ -1324,10 +1324,8 @@ class SQLBaseStore(object):
 
         sql = "DELETE FROM %s" % table
 
-        clauses = []
-        values = []
-        clauses.append("%s IN (%s)" % (column, ",".join("?" for _ in iterable)))
-        values.extend(iterable)
+        clause, values = make_in_list_sql_clause(txn.database_engine, column, iterable)
+        clauses = [clause]
 
         for key, value in iteritems(keyvalues):
             clauses.append("%s = ?" % (key,))
@@ -1694,3 +1692,30 @@ def db_to_json(db_content):
     except Exception:
         logging.warning("Tried to decode '%r' as JSON and failed", db_content)
         raise
+
+
+def make_in_list_sql_clause(
+    database_engine, column: str, iterable: Iterable
+) -> Tuple[str, Iterable]:
+    """Returns an SQL clause that checks the given column is in the iterable.
+
+    On SQLite this expands to `column IN (?, ?, ...)`, whereas on Postgres
+    it expands to `column = ANY(?)`. While both DBs support the `IN` form,
+    using the `ANY` form on postgres means that it views queries with
+    different length iterables as the same, helping the query stats.
+
+    Args:
+        database_engine
+        column: Name of the column
+        iterable: The values to check the column against.
+
+    Returns:
+        A tuple of SQL query and the args
+    """
+
+    if database_engine.supports_using_any_list:
+        # This should hopefully be faster, but also makes postgres query
+        # stats easier to understand.
+        return "%s = ANY(?)" % (column,), [list(iterable)]
+    else:
+        return "%s IN (%s)" % (column, ",".join("?" for _ in iterable)), list(iterable)
diff --git a/synapse/storage/deviceinbox.py b/synapse/storage/deviceinbox.py
index 70bc2bb2cc..f04aad0743 100644
--- a/synapse/storage/deviceinbox.py
+++ b/synapse/storage/deviceinbox.py
@@ -20,7 +20,7 @@ from canonicaljson import json
 from twisted.internet import defer
 
 from synapse.logging.opentracing import log_kv, set_tag, trace
-from synapse.storage._base import SQLBaseStore
+from synapse.storage._base import SQLBaseStore, make_in_list_sql_clause
 from synapse.storage.background_updates import BackgroundUpdateStore
 from synapse.util.caches.expiringcache import ExpiringCache
 
@@ -378,15 +378,15 @@ class DeviceInboxStore(DeviceInboxWorkerStore, DeviceInboxBackgroundUpdateStore)
             else:
                 if not devices:
                     continue
-                sql = (
-                    "SELECT device_id FROM devices"
-                    " WHERE user_id = ? AND device_id IN ("
-                    + ",".join("?" * len(devices))
-                    + ")"
+
+                clause, args = make_in_list_sql_clause(
+                    txn.database_engine, "device_id", devices
                 )
+                sql = "SELECT device_id FROM devices WHERE user_id = ? AND " + clause
+
                 # TODO: Maybe this needs to be done in batches if there are
                 # too many local devices for a given user.
-                txn.execute(sql, [user_id] + devices)
+                txn.execute(sql, [user_id] + list(args))
                 for row in txn:
                     # Only insert into the local inbox if the device exists on
                     # this server
diff --git a/synapse/storage/devices.py b/synapse/storage/devices.py
index 111bfb3d64..ac5239e50a 100644
--- a/synapse/storage/devices.py
+++ b/synapse/storage/devices.py
@@ -28,7 +28,12 @@ from synapse.logging.opentracing import (
     whitelisted_homeserver,
 )
 from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.storage._base import Cache, SQLBaseStore, db_to_json
+from synapse.storage._base import (
+    Cache,
+    SQLBaseStore,
+    db_to_json,
+    make_in_list_sql_clause,
+)
 from synapse.storage.background_updates import BackgroundUpdateStore
 from synapse.util import batch_iter
 from synapse.util.caches.descriptors import cached, cachedInlineCallbacks, cachedList
@@ -448,11 +453,14 @@ class DeviceWorkerStore(SQLBaseStore):
             sql = """
                 SELECT DISTINCT user_id FROM device_lists_stream
                 WHERE stream_id > ?
-                AND user_id IN (%s)
+                AND
             """
 
             for chunk in batch_iter(to_check, 100):
-                txn.execute(sql % (",".join("?" for _ in chunk),), (from_key,) + chunk)
+                clause, args = make_in_list_sql_clause(
+                    txn.database_engine, "user_id", chunk
+                )
+                txn.execute(sql + clause, (from_key,) + tuple(args))
                 changes.update(user_id for user_id, in txn)
 
             return changes
diff --git a/synapse/storage/engines/postgres.py b/synapse/storage/engines/postgres.py
index d670286fa5..b7c4eda338 100644
--- a/synapse/storage/engines/postgres.py
+++ b/synapse/storage/engines/postgres.py
@@ -86,6 +86,12 @@ class PostgresEngine(object):
         """
         return True
 
+    @property
+    def supports_using_any_list(self):
+        """Do we support using `a = ANY(?)` and passing a list
+        """
+        return True
+
     def is_deadlock(self, error):
         if isinstance(error, self.module.DatabaseError):
             # https://www.postgresql.org/docs/current/static/errcodes-appendix.html
diff --git a/synapse/storage/engines/sqlite.py b/synapse/storage/engines/sqlite.py
index ac92109366..ddad17dc5a 100644
--- a/synapse/storage/engines/sqlite.py
+++ b/synapse/storage/engines/sqlite.py
@@ -46,6 +46,12 @@ class Sqlite3Engine(object):
         """
         return self.module.sqlite_version_info >= (3, 15, 0)
 
+    @property
+    def supports_using_any_list(self):
+        """Do we support using `a = ANY(?)` and passing a list
+        """
+        return False
+
     def check_database(self, txn):
         pass
 
diff --git a/synapse/storage/event_federation.py b/synapse/storage/event_federation.py
index f5e8c39262..47cc10d32a 100644
--- a/synapse/storage/event_federation.py
+++ b/synapse/storage/event_federation.py
@@ -25,7 +25,7 @@ from twisted.internet import defer
 
 from synapse.api.errors import StoreError
 from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.storage._base import SQLBaseStore
+from synapse.storage._base import SQLBaseStore, make_in_list_sql_clause
 from synapse.storage.events_worker import EventsWorkerStore
 from synapse.storage.signatures import SignatureWorkerStore
 from synapse.util.caches.descriptors import cached
@@ -68,7 +68,7 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
         else:
             results = set()
 
-        base_sql = "SELECT auth_id FROM event_auth WHERE event_id IN (%s)"
+        base_sql = "SELECT auth_id FROM event_auth WHERE "
 
         front = set(event_ids)
         while front:
@@ -76,7 +76,10 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore, SQLBas
             front_list = list(front)
             chunks = [front_list[x : x + 100] for x in range(0, len(front), 100)]
             for chunk in chunks:
-                txn.execute(base_sql % (",".join(["?"] * len(chunk)),), chunk)
+                clause, args = make_in_list_sql_clause(
+                    txn.database_engine, "event_id", chunk
+                )
+                txn.execute(base_sql + clause, list(args))
                 new_front.update([r[0] for r in txn])
 
             new_front -= results
diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index bb6ff0595a..ee49ef235d 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -39,6 +39,7 @@ from synapse.logging.utils import log_function
 from synapse.metrics import BucketCollector
 from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.state import StateResolutionStore
+from synapse.storage._base import make_in_list_sql_clause
 from synapse.storage.background_updates import BackgroundUpdateStore
 from synapse.storage.event_federation import EventFederationStore
 from synapse.storage.events_worker import EventsWorkerStore
@@ -641,14 +642,16 @@ class EventsStore(
                 LEFT JOIN rejections USING (event_id)
                 LEFT JOIN event_json USING (event_id)
             WHERE
-                prev_event_id IN (%s)
-                AND NOT events.outlier
+                NOT events.outlier
                 AND rejections.event_id IS NULL
-            """ % (
-                ",".join("?" for _ in batch),
+                AND
+            """
+
+            clause, args = make_in_list_sql_clause(
+                self.database_engine, "prev_event_id", batch
             )
 
-            txn.execute(sql, batch)
+            txn.execute(sql + clause, args)
             results.extend(r[0] for r in txn if not json.loads(r[1]).get("soft_failed"))
 
         for chunk in batch_iter(event_ids, 100):
@@ -695,13 +698,15 @@ class EventsStore(
                     LEFT JOIN rejections USING (event_id)
                     LEFT JOIN event_json USING (event_id)
                 WHERE
-                    event_id IN (%s)
-                    AND NOT events.outlier
-                """ % (
-                    ",".join("?" for _ in to_recursively_check),
+                    NOT events.outlier
+                    AND
+                """
+
+                clause, args = make_in_list_sql_clause(
+                    self.database_engine, "event_id", to_recursively_check
                 )
 
-                txn.execute(sql, to_recursively_check)
+                txn.execute(sql + clause, args)
                 to_recursively_check = []
 
                 for event_id, prev_event_id, metadata, rejected in txn:
@@ -1543,10 +1548,14 @@ class EventsStore(
                 " FROM events as e"
                 " LEFT JOIN rejections as rej USING (event_id)"
                 " LEFT JOIN redactions as r ON e.event_id = r.redacts"
-                " WHERE e.event_id IN (%s)"
-            ) % (",".join(["?"] * len(ev_map)),)
+                " WHERE "
+            )
+
+            clause, args = make_in_list_sql_clause(
+                self.database_engine, "e.event_id", list(ev_map)
+            )
 
-            txn.execute(sql, list(ev_map))
+            txn.execute(sql + clause, args)
             rows = self.cursor_to_dict(txn)
             for row in rows:
                 event = ev_map[row["event_id"]]
@@ -2249,11 +2258,12 @@ class EventsStore(
             sql = """
                 SELECT DISTINCT state_group FROM event_to_state_groups
                 LEFT JOIN events_to_purge AS ep USING (event_id)
-                WHERE state_group IN (%s) AND ep.event_id IS NULL
-            """ % (
-                ",".join("?" for _ in current_search),
+                WHERE ep.event_id IS NULL AND
+            """
+            clause, args = make_in_list_sql_clause(
+                txn.database_engine, "state_group", current_search
             )
-            txn.execute(sql, list(current_search))
+            txn.execute(sql + clause, list(args))
 
             referenced = set(sg for sg, in txn)
             referenced_groups |= referenced
diff --git a/synapse/storage/events_bg_updates.py b/synapse/storage/events_bg_updates.py
index e77a7e28af..31ea6f917f 100644
--- a/synapse/storage/events_bg_updates.py
+++ b/synapse/storage/events_bg_updates.py
@@ -21,6 +21,7 @@ from canonicaljson import json
 
 from twisted.internet import defer
 
+from synapse.storage._base import make_in_list_sql_clause
 from synapse.storage.background_updates import BackgroundUpdateStore
 
 logger = logging.getLogger(__name__)
@@ -325,12 +326,13 @@ class EventsBackgroundUpdatesStore(BackgroundUpdateStore):
                     INNER JOIN event_json USING (event_id)
                     LEFT JOIN rejections USING (event_id)
                     WHERE
-                        prev_event_id IN (%s)
-                        AND NOT events.outlier
-                """ % (
-                    ",".join("?" for _ in to_check),
+                        NOT events.outlier
+                        AND
+                """
+                clause, args = make_in_list_sql_clause(
+                    self.database_engine, "prev_event_id", to_check
                 )
-                txn.execute(sql, to_check)
+                txn.execute(sql + clause, list(args))
 
                 for prev_event_id, event_id, metadata, rejected in txn:
                     if event_id in graph:
diff --git a/synapse/storage/events_worker.py b/synapse/storage/events_worker.py
index 57ce0304e9..4c4b76bd93 100644
--- a/synapse/storage/events_worker.py
+++ b/synapse/storage/events_worker.py
@@ -31,12 +31,11 @@ from synapse.events.snapshot import EventContext  # noqa: F401
 from synapse.events.utils import prune_event
 from synapse.logging.context import LoggingContext, PreserveLoggingContext
 from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.storage._base import SQLBaseStore, make_in_list_sql_clause
 from synapse.types import get_domain_from_id
 from synapse.util import batch_iter
 from synapse.util.metrics import Measure
 
-from ._base import SQLBaseStore
-
 logger = logging.getLogger(__name__)
 
 
@@ -623,10 +622,14 @@ class EventsWorkerStore(SQLBaseStore):
                 " rej.reason "
                 " FROM event_json as e"
                 " LEFT JOIN rejections as rej USING (event_id)"
-                " WHERE e.event_id IN (%s)"
-            ) % (",".join(["?"] * len(evs)),)
+                " WHERE "
+            )
 
-            txn.execute(sql, evs)
+            clause, args = make_in_list_sql_clause(
+                txn.database_engine, "e.event_id", evs
+            )
+
+            txn.execute(sql + clause, args)
 
             for row in txn:
                 event_id = row[0]
@@ -640,11 +643,11 @@ class EventsWorkerStore(SQLBaseStore):
                 }
 
             # check for redactions
-            redactions_sql = (
-                "SELECT event_id, redacts FROM redactions WHERE redacts IN (%s)"
-            ) % (",".join(["?"] * len(evs)),)
+            redactions_sql = "SELECT event_id, redacts FROM redactions WHERE "
+
+            clause, args = make_in_list_sql_clause(txn.database_engine, "redacts", evs)
 
-            txn.execute(redactions_sql, evs)
+            txn.execute(redactions_sql + clause, args)
 
             for (redacter, redacted) in txn:
                 d = event_dict.get(redacted)
@@ -753,10 +756,11 @@ class EventsWorkerStore(SQLBaseStore):
         results = set()
 
         def have_seen_events_txn(txn, chunk):
-            sql = "SELECT event_id FROM events as e WHERE e.event_id IN (%s)" % (
-                ",".join("?" * len(chunk)),
+            sql = "SELECT event_id FROM events as e WHERE "
+            clause, args = make_in_list_sql_clause(
+                txn.database_engine, "e.event_id", chunk
             )
-            txn.execute(sql, chunk)
+            txn.execute(sql + clause, args)
             for (event_id,) in txn:
                 results.add(event_id)
 
diff --git a/synapse/storage/presence.py b/synapse/storage/presence.py
index 5db6f2d84a..3a641f538b 100644
--- a/synapse/storage/presence.py
+++ b/synapse/storage/presence.py
@@ -18,11 +18,10 @@ from collections import namedtuple
 from twisted.internet import defer
 
 from synapse.api.constants import PresenceState
+from synapse.storage._base import SQLBaseStore, make_in_list_sql_clause
 from synapse.util import batch_iter
 from synapse.util.caches.descriptors import cached, cachedList
 
-from ._base import SQLBaseStore
-
 
 class UserPresenceState(
     namedtuple(
@@ -119,14 +118,13 @@ class PresenceStore(SQLBaseStore):
         )
 
         # Delete old rows to stop database from getting really big
-        sql = (
-            "DELETE FROM presence_stream WHERE" " stream_id < ?" " AND user_id IN (%s)"
-        )
+        sql = "DELETE FROM presence_stream WHERE stream_id < ? AND "
 
         for states in batch_iter(presence_states, 50):
-            args = [stream_id]
-            args.extend(s.user_id for s in states)
-            txn.execute(sql % (",".join("?" for _ in states),), args)
+            clause, args = make_in_list_sql_clause(
+                self.database_engine, "user_id", [s.user_id for s in states]
+            )
+            txn.execute(sql + clause, [stream_id] + list(args))
 
     def get_all_presence_updates(self, last_id, current_id):
         if last_id == current_id:
diff --git a/synapse/storage/receipts.py b/synapse/storage/receipts.py
index 290ddb30e8..0c24430f28 100644
--- a/synapse/storage/receipts.py
+++ b/synapse/storage/receipts.py
@@ -21,12 +21,11 @@ from canonicaljson import json
 
 from twisted.internet import defer
 
+from synapse.storage._base import SQLBaseStore, make_in_list_sql_clause
+from synapse.storage.util.id_generators import StreamIdGenerator
 from synapse.util.caches.descriptors import cached, cachedInlineCallbacks, cachedList
 from synapse.util.caches.stream_change_cache import StreamChangeCache
 
-from ._base import SQLBaseStore
-from .util.id_generators import StreamIdGenerator
-
 logger = logging.getLogger(__name__)
 
 
@@ -217,24 +216,26 @@ class ReceiptsWorkerStore(SQLBaseStore):
 
         def f(txn):
             if from_key:
-                sql = (
-                    "SELECT * FROM receipts_linearized WHERE"
-                    " room_id IN (%s) AND stream_id > ? AND stream_id <= ?"
-                ) % (",".join(["?"] * len(room_ids)))
-                args = list(room_ids)
-                args.extend([from_key, to_key])
+                sql = """
+                    SELECT * FROM receipts_linearized WHERE
+                    stream_id > ? AND stream_id <= ? AND
+                """
+                clause, args = make_in_list_sql_clause(
+                    self.database_engine, "room_id", room_ids
+                )
 
-                txn.execute(sql, args)
+                txn.execute(sql + clause, [from_key, to_key] + list(args))
             else:
-                sql = (
-                    "SELECT * FROM receipts_linearized WHERE"
-                    " room_id IN (%s) AND stream_id <= ?"
-                ) % (",".join(["?"] * len(room_ids)))
+                sql = """
+                    SELECT * FROM receipts_linearized WHERE
+                    stream_id <= ? AND
+                """
 
-                args = list(room_ids)
-                args.append(to_key)
+                clause, args = make_in_list_sql_clause(
+                    self.database_engine, "room_id", room_ids
+                )
 
-                txn.execute(sql, args)
+                txn.execute(sql + clause, [to_key] + list(args))
 
             return self.cursor_to_dict(txn)
 
@@ -433,13 +434,19 @@ class ReceiptsStore(ReceiptsWorkerStore):
             # we need to points in graph -> linearized form.
             # TODO: Make this better.
             def graph_to_linear(txn):
-                query = (
-                    "SELECT event_id WHERE room_id = ? AND stream_ordering IN ("
-                    " SELECT max(stream_ordering) WHERE event_id IN (%s)"
-                    ")"
-                ) % (",".join(["?"] * len(event_ids)))
+                clause, args = make_in_list_sql_clause(
+                    self.database_engine, "event_id", event_ids
+                )
+
+                sql = """
+                    SELECT event_id WHERE room_id = ? AND stream_ordering IN (
+                        SELECT max(stream_ordering) WHERE %s
+                    )
+                """ % (
+                    clause,
+                )
 
-                txn.execute(query, [room_id] + event_ids)
+                txn.execute(sql, [room_id] + list(args))
                 rows = txn.fetchall()
                 if rows:
                     return rows[0][0]
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index 4e606a8380..ff63487823 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -26,7 +26,7 @@ from twisted.internet import defer
 from synapse.api.constants import EventTypes, Membership
 from synapse.metrics import LaterGauge
 from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.storage._base import LoggingTransaction
+from synapse.storage._base import LoggingTransaction, make_in_list_sql_clause
 from synapse.storage.background_updates import BackgroundUpdateStore
 from synapse.storage.engines import Sqlite3Engine
 from synapse.storage.events_worker import EventsWorkerStore
@@ -372,6 +372,9 @@ class RoomMemberWorkerStore(EventsWorkerStore):
         results = []
         if membership_list:
             if self._current_state_events_membership_up_to_date:
+                clause, args = make_in_list_sql_clause(
+                    self.database_engine, "c.membership", membership_list
+                )
                 sql = """
                     SELECT room_id, e.sender, c.membership, event_id, e.stream_ordering
                     FROM current_state_events AS c
@@ -379,11 +382,14 @@ class RoomMemberWorkerStore(EventsWorkerStore):
                     WHERE
                         c.type = 'm.room.member'
                         AND state_key = ?
-                        AND c.membership IN (%s)
+                        AND %s
                 """ % (
-                    ",".join("?" * len(membership_list))
+                    clause,
                 )
             else:
+                clause, args = make_in_list_sql_clause(
+                    self.database_engine, "m.membership", membership_list
+                )
                 sql = """
                     SELECT room_id, e.sender, m.membership, event_id, e.stream_ordering
                     FROM current_state_events AS c
@@ -392,12 +398,12 @@ class RoomMemberWorkerStore(EventsWorkerStore):
                     WHERE
                         c.type = 'm.room.member'
                         AND state_key = ?
-                        AND m.membership IN (%s)
+                        AND %s
                 """ % (
-                    ",".join("?" * len(membership_list))
+                    clause,
                 )
 
-            txn.execute(sql, (user_id, *membership_list))
+            txn.execute(sql, (user_id, *args))
             results = [RoomsForUser(**r) for r in self.cursor_to_dict(txn)]
 
         if do_invite:
diff --git a/synapse/storage/search.py b/synapse/storage/search.py
index 6ba4190f1a..7695bf09fc 100644
--- a/synapse/storage/search.py
+++ b/synapse/storage/search.py
@@ -24,6 +24,7 @@ from canonicaljson import json
 from twisted.internet import defer
 
 from synapse.api.errors import SynapseError
+from synapse.storage._base import make_in_list_sql_clause
 from synapse.storage.engines import PostgresEngine, Sqlite3Engine
 
 from .background_updates import BackgroundUpdateStore
@@ -385,8 +386,10 @@ class SearchStore(SearchBackgroundUpdateStore):
         # Make sure we don't explode because the person is in too many rooms.
         # We filter the results below regardless.
         if len(room_ids) < 500:
-            clauses.append("room_id IN (%s)" % (",".join(["?"] * len(room_ids)),))
-            args.extend(room_ids)
+            clause, args = make_in_list_sql_clause(
+                self.database_engine, "room_id", room_ids
+            )
+            clauses = [clause]
 
         local_clauses = []
         for key in keys:
@@ -492,8 +495,10 @@ class SearchStore(SearchBackgroundUpdateStore):
         # Make sure we don't explode because the person is in too many rooms.
         # We filter the results below regardless.
         if len(room_ids) < 500:
-            clauses.append("room_id IN (%s)" % (",".join(["?"] * len(room_ids)),))
-            args.extend(room_ids)
+            clause, args = make_in_list_sql_clause(
+                self.database_engine, "room_id", room_ids
+            )
+            clauses = [clause]
 
         local_clauses = []
         for key in keys:
diff --git a/synapse/storage/user_erasure_store.py b/synapse/storage/user_erasure_store.py
index 05cabc2282..aa4f0da5f0 100644
--- a/synapse/storage/user_erasure_store.py
+++ b/synapse/storage/user_erasure_store.py
@@ -56,15 +56,15 @@ class UserErasureWorkerStore(SQLBaseStore):
         # iterate it multiple times, and (b) avoiding duplicates.
         user_ids = tuple(set(user_ids))
 
-        def _get_erased_users(txn):
-            txn.execute(
-                "SELECT user_id FROM erased_users WHERE user_id IN (%s)"
-                % (",".join("?" * len(user_ids))),
-                user_ids,
-            )
-            return set(r[0] for r in txn)
-
-        erased_users = yield self.runInteraction("are_users_erased", _get_erased_users)
+        rows = yield self._simple_select_many_batch(
+            table="erased_users",
+            column="user_id",
+            iterable=user_ids,
+            retcols=("user_id",),
+            desc="are_users_erased",
+        )
+        erased_users = set(row["user_id"] for row in rows)
+
         res = dict((u, u in erased_users) for u in user_ids)
         return res