From ff7cc17b5706ff3f386b15fda668511c0502ab9c Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Wed, 8 Dec 2021 14:15:14 +0000
Subject: [PATCH] Improve log messages for stream ids (#11536)

Somehow I'd managed to get my database in a pickle with stream ids. These
changes were useful to debug.
---
 changelog.d/11536.misc                         | 1 +
 synapse/storage/databases/main/state_deltas.py | 4 +++-
 synapse/storage/util/id_generators.py          | 6 +++---
 3 files changed, 7 insertions(+), 4 deletions(-)
 create mode 100644 changelog.d/11536.misc

diff --git a/changelog.d/11536.misc b/changelog.d/11536.misc
new file mode 100644
index 000000000..b9191c111
--- /dev/null
+++ b/changelog.d/11536.misc
@@ -0,0 +1 @@
+Improvements to log messages around handling stream ids.
diff --git a/synapse/storage/databases/main/state_deltas.py b/synapse/storage/databases/main/state_deltas.py
index 7f3624b12..188afec33 100644
--- a/synapse/storage/databases/main/state_deltas.py
+++ b/synapse/storage/databases/main/state_deltas.py
@@ -56,7 +56,9 @@ class StateDeltasStore(SQLBaseStore):
         prev_stream_id = int(prev_stream_id)
 
         # check we're not going backwards
-        assert prev_stream_id <= max_stream_id
+        assert (
+            prev_stream_id <= max_stream_id
+        ), f"New stream id {max_stream_id} is smaller than prev stream id {prev_stream_id}"
 
         if not self._curr_state_delta_stream_cache.has_any_entity_changed(
             prev_stream_id
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
index 4ff301390..b8112e1c0 100644
--- a/synapse/storage/util/id_generators.py
+++ b/synapse/storage/util/id_generators.py
@@ -74,8 +74,6 @@ class IdGenerator:
 def _load_current_id(
     db_conn: LoggingDatabaseConnection, table: str, column: str, step: int = 1
 ) -> int:
-    # debug logging for https://github.com/matrix-org/synapse/issues/7968
-    logger.info("initialising stream generator for %s(%s)", table, column)
     cur = db_conn.cursor(txn_name="_load_current_id")
     if step == 1:
         cur.execute("SELECT MAX(%s) FROM %s" % (column, table))
@@ -86,7 +84,9 @@ def _load_current_id(
     (val,) = result
     cur.close()
     current_id = int(val) if val else step
-    return (max if step > 0 else min)(current_id, step)
+    res = (max if step > 0 else min)(current_id, step)
+    logger.info("Initialising stream generator for %s(%s): %i", table, column, res)
+    return res
 
 
 class AbstractStreamIdTracker(metaclass=abc.ABCMeta):