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

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

This reverts commit 82c1ee1c22a87b9e6e3179947014b0f11c0a1ac3.

* Changelog

1 files changed, 4 insertions, 6 deletions

diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
index 8fd21c2bf8..9f3d23f0a5 100644
--- a/synapse/storage/util/id_generators.py
+++ b/synapse/storage/util/id_generators.py
@@ -231,12 +231,8 @@ class MultiWriterIdGenerator:
         # gaps should be relatively rare it's still worth doing the book keeping
         # that allows us to skip forwards when there are gapless runs of
         # positions.
-        #
-        # We start at 1 here as a) the first generated stream ID will be 2, and
-        # b) other parts of the code assume that stream IDs are strictly greater
-        # than 0.
         self._persisted_upto_position = (
-            min(self._current_positions.values()) if self._current_positions else 1
+            min(self._current_positions.values()) if self._current_positions else 0
         )
         self._known_persisted_positions = []  # type: List[int]
 
@@ -366,7 +362,9 @@ class MultiWriterIdGenerator:
         equal to it have been successfully persisted.
         """
 
-        return self.get_persisted_upto_position()
+        # Currently we don't support this operation, as it's not obvious how to
+        # condense the stream positions of multiple writers into a single int.
+        raise NotImplementedError()
 
     def get_current_token_for_writer(self, instance_name: str) -> int:
         """Returns the position of the given writer.