Revert "Add experimental support for sharding event persister. (#8170)" (#8242)

* Revert "Add experimental support for sharding event persister. (#8170)"

This reverts commit 82c1ee1c22a87b9e6e3179947014b0f11c0a1ac3.

* Changelog

3 files changed, 13 insertions, 46 deletions

diff --git a/synapse/config/_base.py b/synapse/config/_base.py
index 73f0717b0d..1417487427 100644
--- a/synapse/config/_base.py
+++ b/synapse/config/_base.py
@@ -832,26 +832,11 @@ class ShardedWorkerHandlingConfig:
     def should_handle(self, instance_name: str, key: str) -> bool:
         """Whether this instance is responsible for handling the given key.
         """
-        # If multiple instances are not defined we always return true
+
+        # If multiple instances are not defined we always return true.
         if not self.instances or len(self.instances) == 1:
             return True
 
-        return self.get_instance(key) == instance_name
-
-    def get_instance(self, key: str) -> str:
-        """Get the instance responsible for handling the given key.
-
-        Note: For things like federation sending the config for which instance
-        is sending is known only to the sender instance if there is only one.
-        Therefore `should_handle` should be used where possible.
-        """
-
-        if not self.instances:
-            return "master"
-
-        if len(self.instances) == 1:
-            return self.instances[0]
-
         # We shard by taking the hash, modulo it by the number of instances and
         # then checking whether this instance matches the instance at that
         # index.
@@ -861,7 +846,7 @@ class ShardedWorkerHandlingConfig:
         dest_hash = sha256(key.encode("utf8")).digest()
         dest_int = int.from_bytes(dest_hash, byteorder="little")
         remainder = dest_int % (len(self.instances))
-        return self.instances[remainder]
+        return self.instances[remainder] == instance_name
 
 
 __all__ = ["Config", "RootConfig", "ShardedWorkerHandlingConfig"]
diff --git a/synapse/config/_base.pyi b/synapse/config/_base.pyi
index b8faafa9bd..eb911e8f9f 100644
--- a/synapse/config/_base.pyi
+++ b/synapse/config/_base.pyi
@@ -142,4 +142,3 @@ class ShardedWorkerHandlingConfig:
     instances: List[str]
     def __init__(self, instances: List[str]) -> None: ...
     def should_handle(self, instance_name: str, key: str) -> bool: ...
-    def get_instance(self, key: str) -> str: ...
diff --git a/synapse/config/workers.py b/synapse/config/workers.py
index f23e42cdf9..c784a71508 100644
--- a/synapse/config/workers.py
+++ b/synapse/config/workers.py
@@ -13,24 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import List, Union
-
 import attr
 
 from ._base import Config, ConfigError, ShardedWorkerHandlingConfig
 from .server import ListenerConfig, parse_listener_def
 
 
-def _instance_to_list_converter(obj: Union[str, List[str]]) -> List[str]:
-    """Helper for allowing parsing a string or list of strings to a config
-    option expecting a list of strings.
-    """
-
-    if isinstance(obj, str):
-        return [obj]
-    return obj
-
-
 @attr.s
 class InstanceLocationConfig:
     """The host and port to talk to an instance via HTTP replication.
@@ -45,13 +33,11 @@ class WriterLocations:
     """Specifies the instances that write various streams.
 
     Attributes:
-        events: The instances that write to the event and backfill streams.
-        typing: The instance that writes to the typing stream.
+        events: The instance that writes to the event and backfill streams.
+        events: The instance that writes to the typing stream.
     """
 
-    events = attr.ib(
-        default=["master"], type=List[str], converter=_instance_to_list_converter
-    )
+    events = attr.ib(default="master", type=str)
     typing = attr.ib(default="master", type=str)
 
 
@@ -119,18 +105,15 @@ class WorkerConfig(Config):
         writers = config.get("stream_writers") or {}
         self.writers = WriterLocations(**writers)
 
-        # Check that the configured writers for events and typing also appears in
+        # Check that the configured writer for events and typing also appears in
         # `instance_map`.
         for stream in ("events", "typing"):
-            instances = _instance_to_list_converter(getattr(self.writers, stream))
-            for instance in instances:
-                if instance != "master" and instance not in self.instance_map:
-                    raise ConfigError(
-                        "Instance %r is configured to write %s but does not appear in `instance_map` config."
-                        % (instance, stream)
-                    )
-
-        self.events_shard_config = ShardedWorkerHandlingConfig(self.writers.events)
+            instance = getattr(self.writers, stream)
+            if instance != "master" and instance not in self.instance_map:
+                raise ConfigError(
+                    "Instance %r is configured to write %s but does not appear in `instance_map` config."
+                    % (instance, stream)
+                )
 
     def generate_config_section(self, config_dir_path, server_name, **kwargs):
         return """\