skip some dict munging in event persistence (#11560)

Create a new dict helper method `simple_insert_many_values_txn`, which takes
raw row values, rather than {key=>value} dicts. This saves us a bunch of dict
munging, and makes it easier to use generators rather than creating
intermediate lists and dicts.

changelog.d/11560.misc

@@ -0,0 +1 @@
+Minor efficiency improvements in event persistence.

synapse/storage/database.py

@@ -896,6 +896,9 @@ class DatabasePool:
     ) -> None:
         """Executes an INSERT query on the named table.
 
+        The input is given as a list of dicts, with one dict per row.
+        Generally simple_insert_many_values should be preferred for new code.
+
         Args:
             table: string giving the table name
             values: dict of new column names and values for them
@@ -909,6 +912,9 @@ class DatabasePool:
     ) -> None:
         """Executes an INSERT query on the named table.
 
+        The input is given as a list of dicts, with one dict per row.
+        Generally simple_insert_many_values_txn should be preferred for new code.
+
         Args:
             txn: The transaction to use.
             table: string giving the table name
@@ -933,23 +939,66 @@ class DatabasePool:
             if k != keys[0]:
                 raise RuntimeError("All items must have the same keys")
 
+        return DatabasePool.simple_insert_many_values_txn(txn, table, keys[0], vals)
+
+    async def simple_insert_many_values(
+        self,
+        table: str,
+        keys: Collection[str],
+        values: Iterable[Iterable[Any]],
+        desc: str,
+    ) -> None:
+        """Executes an INSERT query on the named table.
+
+        The input is given as a list of rows, where each row is a list of values.
+        (Actually any iterable is fine.)
+
+        Args:
+            table: string giving the table name
+            keys: list of column names
+            values: for each row, a list of values in the same order as `keys`
+            desc: description of the transaction, for logging and metrics
+        """
+        await self.runInteraction(
+            desc, self.simple_insert_many_values_txn, table, keys, values
+        )
+
+    @staticmethod
+    def simple_insert_many_values_txn(
+        txn: LoggingTransaction,
+        table: str,
+        keys: Collection[str],
+        values: Iterable[Iterable[Any]],
+    ) -> None:
+        """Executes an INSERT query on the named table.
+
+        The input is given as a list of rows, where each row is a list of values.
+        (Actually any iterable is fine.)
+
+        Args:
+            txn: The transaction to use.
+            table: string giving the table name
+            keys: list of column names
+            values: for each row, a list of values in the same order as `keys`
+        """
+
         if isinstance(txn.database_engine, PostgresEngine):
             # We use `execute_values` as it can be a lot faster than `execute_batch`,
             # but it's only available on postgres.
             sql = "INSERT INTO %s (%s) VALUES ?" % (
                 table,
-                ", ".join(k for k in keys[0]),
+                ", ".join(k for k in keys),
             )
 
-            txn.execute_values(sql, vals, fetch=False)
+            txn.execute_values(sql, values, fetch=False)
         else:
             sql = "INSERT INTO %s (%s) VALUES(%s)" % (
                 table,
-                ", ".join(k for k in keys[0]),
-                ", ".join("?" for _ in keys[0]),
+                ", ".join(k for k in keys),
+                ", ".join("?" for _ in keys),
             )
 
-            txn.execute_batch(sql, vals)
+            txn.execute_batch(sql, values)
 
     async def simple_upsert(
         self,

synapse/storage/databases/main/events.py

@@ -19,6 +19,7 @@ from collections import OrderedDict
 from typing import (
     TYPE_CHECKING,
     Any,
+    Collection,
     Dict,
     Generator,
     Iterable,
@@ -1319,14 +1320,13 @@ class PersistEventsStore:
 
         return [ec for ec in events_and_contexts if ec[0] not in to_remove]
 
-    def _store_event_txn(self, txn, events_and_contexts):
+    def _store_event_txn(
+        self,
+        txn: LoggingTransaction,
+        events_and_contexts: Collection[Tuple[EventBase, EventContext]],
+    ) -> None:
         """Insert new events into the event, event_json, redaction and
         state_events tables.
-
-        Args:
-            txn (twisted.enterprise.adbapi.Connection): db connection
-            events_and_contexts (list[(EventBase, EventContext)]): events
-                we are persisting
         """
 
         if not events_and_contexts:
@@ -1339,46 +1339,58 @@ class PersistEventsStore:
             d.pop("redacted_because", None)
             return d
 
-        self.db_pool.simple_insert_many_txn(
+        self.db_pool.simple_insert_many_values_txn(
             txn,
             table="event_json",
-            values=[
-                {
-                    "event_id": event.event_id,
-                    "room_id": event.room_id,
-                    "internal_metadata": json_encoder.encode(
-                        event.internal_metadata.get_dict()
-                    ),
-                    "json": json_encoder.encode(event_dict(event)),
-                    "format_version": event.format_version,
-                }
+            keys=("event_id", "room_id", "internal_metadata", "json", "format_version"),
+            values=(
+                (
+                    event.event_id,
+                    event.room_id,
+                    json_encoder.encode(event.internal_metadata.get_dict()),
+                    json_encoder.encode(event_dict(event)),
+                    event.format_version,
+                )
                 for event, _ in events_and_contexts
-            ],
+            ),
         )
 
-        self.db_pool.simple_insert_many_txn(
+        self.db_pool.simple_insert_many_values_txn(
             txn,
             table="events",
-            values=[
-                {
-                    "instance_name": self._instance_name,
-                    "stream_ordering": event.internal_metadata.stream_ordering,
-                    "topological_ordering": event.depth,
-                    "depth": event.depth,
-                    "event_id": event.event_id,
-                    "room_id": event.room_id,
-                    "type": event.type,
-                    "processed": True,
-                    "outlier": event.internal_metadata.is_outlier(),
-                    "origin_server_ts": int(event.origin_server_ts),
-                    "received_ts": self._clock.time_msec(),
-                    "sender": event.sender,
-                    "contains_url": (
-                        "url" in event.content and isinstance(event.content["url"], str)
-                    ),
-                }
+            keys=(
+                "instance_name",
+                "stream_ordering",
+                "topological_ordering",
+                "depth",
+                "event_id",
+                "room_id",
+                "type",
+                "processed",
+                "outlier",
+                "origin_server_ts",
+                "received_ts",
+                "sender",
+                "contains_url",
+            ),
+            values=(
+                (
+                    self._instance_name,
+                    event.internal_metadata.stream_ordering,
+                    event.depth,  # topological_ordering
+                    event.depth,  # depth
+                    event.event_id,
+                    event.room_id,
+                    event.type,
+                    True,  # processed
+                    event.internal_metadata.is_outlier(),
+                    int(event.origin_server_ts),
+                    self._clock.time_msec(),
+                    event.sender,
+                    "url" in event.content and isinstance(event.content["url"], str),
+                )
                 for event, _ in events_and_contexts
-            ],
+            ),
         )
 
         # If we're persisting an unredacted event we go and ensure
@@ -1397,23 +1409,15 @@ class PersistEventsStore:
         )
         txn.execute(sql + clause, [False] + args)
 
-        state_events_and_contexts = [
-            ec for ec in events_and_contexts if ec[0].is_state()
-        ]
-
-        state_values = []
-        for event, _ in state_events_and_contexts:
-            vals = {
-                "event_id": event.event_id,
-                "room_id": event.room_id,
-                "type": event.type,
-                "state_key": event.state_key,
-            }
-
-            state_values.append(vals)
-
-        self.db_pool.simple_insert_many_txn(
-            txn, table="state_events", values=state_values
+        self.db_pool.simple_insert_many_values_txn(
+            txn,
+            table="state_events",
+            keys=("event_id", "room_id", "type", "state_key"),
+            values=(
+                (event.event_id, event.room_id, event.type, event.state_key)
+                for event, _ in events_and_contexts
+                if event.is_state()
+            ),
         )
 
     def _store_rejected_events_txn(self, txn, events_and_contexts):