diff --git a/synapse/storage/schema/delta/40/device_list_streams.sql b/synapse/storage/schema/delta/40/device_list_streams.sql
index d1051c6ddf..8348c143c3 100644
--- a/synapse/storage/schema/delta/40/device_list_streams.sql
+++ b/synapse/storage/schema/delta/40/device_list_streams.sql
@@ -13,7 +13,7 @@
* limitations under the License.
*/
-
+-- Cache of remote devices.
CREATE TABLE device_lists_remote_cache (
user_id TEXT NOT NULL,
device_id TEXT NOT NULL,
@@ -23,6 +23,8 @@ CREATE TABLE device_lists_remote_cache (
CREATE INDEX device_lists_remote_cache_id ON device_lists_remote_cache(user_id, device_id);
+-- The last update we got for a user. Empty if we're not receiving updates for
+-- that user.
CREATE TABLE device_lists_remote_extremeties (
user_id TEXT NOT NULL,
stream_id TEXT NOT NULL
@@ -31,6 +33,7 @@ CREATE TABLE device_lists_remote_extremeties (
CREATE INDEX device_lists_remote_extremeties_id ON device_lists_remote_extremeties(user_id, stream_id);
+-- Stream of device lists updates. Includes both local and remotes
CREATE TABLE device_lists_stream (
stream_id BIGINT NOT NULL,
user_id TEXT NOT NULL,
@@ -40,6 +43,9 @@ CREATE TABLE device_lists_stream (
CREATE INDEX device_lists_stream_id ON device_lists_stream(stream_id, user_id);
+-- The stream of updates to send to other servers. We keep at least one row
+-- per user that was sent so that the prev_id for any new updates can be
+-- calculated
CREATE TABLE device_lists_outbound_pokes (
destination TEXT NOT NULL,
stream_id BIGINT NOT NULL,
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