From 485d999c8a95f8fdc6425a00e906e86efc77a917 Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Mon, 5 Sep 2016 14:49:08 +0100
Subject: [PATCH] Correctly delete old state groups in purge history API

---
 synapse/storage/events.py                 | 99 ++++++++++++++++++-----
 synapse/storage/schema/delta/35/state.sql |  1 +
 2 files changed, 80 insertions(+), 20 deletions(-)

diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 7e9b35151..bec35ea68 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -1578,26 +1578,85 @@ class EventsStore(SQLBaseStore):
 
         # Get all state groups that are only referenced by events that are
         # to be deleted.
-        # txn.execute(
-        #     "SELECT state_group FROM event_to_state_groups"
-        #     " INNER JOIN events USING (event_id)"
-        #     " WHERE state_group IN ("
-        #     "   SELECT DISTINCT state_group FROM events"
-        #     "   INNER JOIN event_to_state_groups USING (event_id)"
-        #     "   WHERE room_id = ? AND topological_ordering < ?"
-        #     " )"
-        #     " GROUP BY state_group HAVING MAX(topological_ordering) < ?",
-        #     (room_id, topological_ordering, topological_ordering)
-        # )
-        # state_rows = txn.fetchall()
-        # txn.executemany(
-        #     "DELETE FROM state_groups_state WHERE state_group = ?",
-        #     state_rows
-        # )
-        # txn.executemany(
-        #     "DELETE FROM state_groups WHERE id = ?",
-        #     state_rows
-        # )
+        txn.execute(
+            "SELECT state_group FROM event_to_state_groups"
+            " INNER JOIN events USING (event_id)"
+            " WHERE state_group IN ("
+            "   SELECT DISTINCT state_group FROM events"
+            "   INNER JOIN event_to_state_groups USING (event_id)"
+            "   WHERE room_id = ? AND topological_ordering < ?"
+            " )"
+            " GROUP BY state_group HAVING MAX(topological_ordering) < ?",
+            (room_id, topological_ordering, topological_ordering)
+        )
+
+        state_rows = txn.fetchall()
+        state_groups_to_delete = [sg for sg, in state_rows]
+
+        # Now we get all the state groups that rely on these state groups
+        new_state_edges = []
+        chunks = [
+            state_groups_to_delete[i:i + 100]
+            for i in xrange(0, len(state_groups_to_delete), 100)
+        ]
+        for chunk in chunks:
+            rows = self._simple_select_many_txn(
+                txn,
+                table="state_group_edges",
+                column="prev_state_group",
+                iterable=chunk,
+                retcols=["state_group"],
+                keyvalues={},
+            )
+            new_state_edges.extend(row["state_group"] for row in rows)
+
+        # Now we turn the state groups that reference to-be-deleted state groups
+        # to non delta versions.
+        for new_state_edge in new_state_edges:
+            curr_state = self._get_state_groups_from_groups_txn(
+                txn, [new_state_edge], types=None
+            )
+            curr_state = curr_state.values()[0]
+
+            self._simple_delete_txn(
+                txn,
+                table="state_groups_state",
+                keyvalues={
+                    "state_group": new_state_edge,
+                }
+            )
+
+            self._simple_delete_txn(
+                txn,
+                table="state_group_edges",
+                keyvalues={
+                    "state_group": new_state_edge,
+                }
+            )
+
+            self._simple_insert_many_txn(
+                txn,
+                table="state_groups_state",
+                values=[
+                    {
+                        "state_group": new_state_edge,
+                        "room_id": room_id,
+                        "type": key[0],
+                        "state_key": key[1],
+                        "event_id": state_id,
+                    }
+                    for key, state_id in curr_state.items()
+                ],
+            )
+
+        txn.executemany(
+            "DELETE FROM state_groups_state WHERE state_group = ?",
+            state_rows
+        )
+        txn.executemany(
+            "DELETE FROM state_groups WHERE id = ?",
+            state_rows
+        )
         # Delete all non-state
         txn.executemany(
             "DELETE FROM event_to_state_groups WHERE event_id = ?",
diff --git a/synapse/storage/schema/delta/35/state.sql b/synapse/storage/schema/delta/35/state.sql
index c4c244c16..0f1fa68a8 100644
--- a/synapse/storage/schema/delta/35/state.sql
+++ b/synapse/storage/schema/delta/35/state.sql
@@ -19,3 +19,4 @@ CREATE TABLE state_group_edges(
 );
 
 CREATE INDEX state_group_edges_idx ON state_group_edges(state_group);
+CREATE INDEX state_group_edges_prev_idx ON state_group_edges(prev_state_group);