From ab80cea3d1c4e10b641880ead2cdb70d23b7ff12 Mon Sep 17 00:00:00 2001
From: Till Faelligen <2353100+S7evinK@users.noreply.github.com>
Date: Wed, 1 Feb 2023 14:10:59 +0100
Subject: [PATCH] Add comments about queries

---
 roomserver/storage/postgres/state_snapshot_table.go  | 2 ++
 syncapi/storage/postgres/output_room_events_table.go | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/roomserver/storage/postgres/state_snapshot_table.go b/roomserver/storage/postgres/state_snapshot_table.go
index 0c5afec07..0e83cfc25 100644
--- a/roomserver/storage/postgres/state_snapshot_table.go
+++ b/roomserver/storage/postgres/state_snapshot_table.go
@@ -99,6 +99,8 @@ const bulkSelectStateForHistoryVisibilitySQL = `
 	  AND (event_type_nid = 7 OR event_state_key LIKE '%:' || $2);
 `
 
+// bulkSelectMembershipForHistoryVisibilitySQL is an optimization to get membership events for a specific user for defined set of events.
+// Returns the event_id of the event we want the membership event for, the event_id of the membership event and the membership event JSON.
 const bulkSelectMembershipForHistoryVisibilitySQL = `
 SELECT re.event_id, re2.event_id, rej.event_json
 FROM roomserver_events re
diff --git a/syncapi/storage/postgres/output_room_events_table.go b/syncapi/storage/postgres/output_room_events_table.go
index 31b4753a1..635853631 100644
--- a/syncapi/storage/postgres/output_room_events_table.go
+++ b/syncapi/storage/postgres/output_room_events_table.go
@@ -107,6 +107,8 @@ const selectRecentEventsSQL = "" +
 	" AND ( $7::text[] IS NULL OR NOT(type LIKE ANY($7)) )" +
 	" ORDER BY id DESC LIMIT $8"
 
+// selectRecentEventsForSyncSQL contains an optimization to get the recent events for a list of rooms, using a LATERAL JOIN
+// The sub select inside LATERAL () is executed for all room_ids it gets as a parameter $1
 const selectRecentEventsForSyncSQL = `
 WITH room_ids AS (
      SELECT unnest($1::text[]) AS room_id