Rewrite Datastore.get_server_verify_keys

Rewrite this so that it doesn't hammer the database.

synapse/storage/keys.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2019 New Vector Ltd.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -13,15 +14,15 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import itertools
 import logging
 
 import six
 
 from signedjson.key import decode_verify_key_bytes
 
-from twisted.internet import defer
-
-from synapse.util.caches.descriptors import cachedInlineCallbacks
+from synapse.util import batch_iter
+from synapse.util.caches.descriptors import cached, cachedList
 
 from ._base import SQLBaseStore
 
@@ -38,36 +39,50 @@ else:
 class KeyStore(SQLBaseStore):
     """Persistence for signature verification keys
     """
-    @cachedInlineCallbacks()
-    def _get_server_verify_key(self, server_name, key_id):
-        verify_key_bytes = yield self._simple_select_one_onecol(
-            table="server_signature_keys",
-            keyvalues={"server_name": server_name, "key_id": key_id},
-            retcol="verify_key",
-            desc="_get_server_verify_key",
-            allow_none=True,
-        )
 
-        if verify_key_bytes:
-            defer.returnValue(decode_verify_key_bytes(key_id, bytes(verify_key_bytes)))
+    @cached()
+    def _get_server_verify_key(self, server_name_and_key_id):
+        raise NotImplementedError()
 
-    @defer.inlineCallbacks
-    def get_server_verify_keys(self, server_name, key_ids):
-        """Retrieve the NACL verification key for a given server for the given
-        key_ids
+    @cachedList(
+        cached_method_name="_get_server_verify_key", list_name="server_name_and_key_ids"
+    )
+    def get_server_verify_keys(self, server_name_and_key_ids):
+        """
         Args:
-            server_name (str): The name of the server.
-            key_ids (iterable[str]): key_ids to try and look up.
+            server_name_and_key_ids (iterable[Tuple[str, str]]):
+                iterable of (server_name, key-id) tuples to fetch keys for
+
         Returns:
-            Deferred: resolves to dict[str, VerifyKey]: map from
-               key_id to verification key.
+            Deferred: resolves to dict[Tuple[str, str], VerifyKey|None]:
+                map from (server_name, key_id) -> VerifyKey, or None if the key is
+                unknown
         """
         keys = {}
-        for key_id in key_ids:
-            key = yield self._get_server_verify_key(server_name, key_id)
-            if key:
-                keys[key_id] = key
-        defer.returnValue(keys)
+
+        def _get_keys(txn, batch):
+            """Processes a batch of keys to fetch, and adds the result to `keys`."""
+
+            # batch_iter always returns tuples so it's safe to do len(batch)
+            sql = (
+                "SELECT server_name, key_id, verify_key FROM server_signature_keys "
+                "WHERE 1=0"
+            ) + " OR (server_name=? AND key_id=?)" * len(batch)
+
+            txn.execute(sql, tuple(itertools.chain.from_iterable(batch)))
+
+            for row in txn:
+                server_name, key_id, key_bytes = row
+                keys[(server_name, key_id)] = decode_verify_key_bytes(
+                    key_id, bytes(key_bytes)
+                )
+
+        def _txn(txn):
+            for batch in batch_iter(server_name_and_key_ids, 50):
+                _get_keys(txn, batch)
+            return keys
+
+        return self.runInteraction("get_server_verify_keys", _txn)
 
     def store_server_verify_key(
         self, server_name, from_server, time_now_ms, verify_key
@@ -93,8 +108,11 @@ class KeyStore(SQLBaseStore):
                     "verify_key": db_binary_type(verify_key.encode()),
                 },
             )
+            # invalidate takes a tuple corresponding to the params of
+            # _get_server_verify_key. _get_server_verify_key only takes one
+            # param, which is itself the 2-tuple (server_name, key_id).
             txn.call_after(
-                self._get_server_verify_key.invalidate, (server_name, key_id)
+                self._get_server_verify_key.invalidate, ((server_name, key_id),)
             )
 
         return self.runInteraction("store_server_verify_key", _txn)