From 513188aa56bc680a54dbdf6d40657da72c5c6877 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Wed, 7 Sep 2016 14:53:19 +0100
Subject: [PATCH] Comment

---
 synapse/storage/state.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/synapse/storage/state.py b/synapse/storage/state.py
index 382f308a6..d6643473d 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -315,6 +315,10 @@ class StateStore(SQLBaseStore):
             # against `state_groups_state` to fetch the latest state.
             # It assumes that previous state groups are always numerically
             # lesser.
+            # The PARTITION is used to get the event_id in the greatest state
+            # group for the given type, state_key.
+            # This may return multiple rows per (type, state_key), but last_value
+            # should be the same.
             sql = ("""
                 WITH RECURSIVE state(state_group) AS (
                     VALUES(?::bigint)