From 8fd8e72cec8df94403441664d8eecc25fa8d363f Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Thu, 12 Nov 2015 15:33:47 +0000
Subject: [PATCH] Expand comment

---
 synapse/storage/search.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/synapse/storage/search.py b/synapse/storage/search.py
index 0b00ddb9d..dcc5ac65a 100644
--- a/synapse/storage/search.py
+++ b/synapse/storage/search.py
@@ -254,6 +254,12 @@ class SearchStore(BackgroundUpdateStore):
         elif isinstance(self.database_engine, Sqlite3Engine):
             # We use CROSS JOIN here to ensure we use the right indexes.
             # https://sqlite.org/optoverview.html#crossjoin
+            #
+            # We want to use the full text search index on event_search to
+            # extract all possible matches first, then lookup those matches
+            # in the events table to get the topological ordering. We need
+            # to use the indexes in this order because sqlite refuses to 
+            # MATCH unless it uses the full text search index
             sql = (
                 "SELECT rank(matchinfo) as rank, room_id, event_id,"
                 " topological_ordering, stream_ordering"