Add `/_dendrite/admin/purgeRoom/{roomID}` (#2662)

This adds a new admin endpoint `/_dendrite/admin/purgeRoom/{roomID}`. It
completely erases all database entries for a given room ID.

The roomserver will start by clearing all data for that room and then
will generate an output event to notify downstream components (i.e. the
sync API and federation API) to do the same.

It does not currently clear media and it is currently not implemented
for SQLite since it relies on SQL array operations right now.

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>
Co-authored-by: Till Faelligen <2353100+S7evinK@users.noreply.github.com>

11 files changed, 382 insertions, 3 deletions

diff --git a/roomserver/storage/interface.go b/roomserver/storage/interface.go
index 92bc2e66..e0b9c56b 100644
--- a/roomserver/storage/interface.go
+++ b/roomserver/storage/interface.go
@@ -173,5 +173,6 @@ type Database interface {
 
 	GetHistoryVisibilityState(ctx context.Context, roomInfo *types.RoomInfo, eventID string, domain string) ([]*gomatrixserverlib.Event, error)
 	GetLeftUsers(ctx context.Context, userIDs []string) ([]string, error)
+	PurgeRoom(ctx context.Context, roomID string) error
 	UpgradeRoom(ctx context.Context, oldRoomID, newRoomID, eventSender string) error
 }
diff --git a/roomserver/storage/postgres/purge_statements.go b/roomserver/storage/postgres/purge_statements.go
new file mode 100644
index 00000000..efba439b
--- /dev/null
+++ b/roomserver/storage/postgres/purge_statements.go
@@ -0,0 +1,133 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/types"
+)
+
+const purgeEventJSONSQL = "" +
+	"DELETE FROM roomserver_event_json WHERE event_nid = ANY(" +
+	"	SELECT event_nid FROM roomserver_events WHERE room_nid = $1" +
+	")"
+
+const purgeEventsSQL = "" +
+	"DELETE FROM roomserver_events WHERE room_nid = $1"
+
+const purgeInvitesSQL = "" +
+	"DELETE FROM roomserver_invites WHERE room_nid = $1"
+
+const purgeMembershipsSQL = "" +
+	"DELETE FROM roomserver_membership WHERE room_nid = $1"
+
+const purgePreviousEventsSQL = "" +
+	"DELETE FROM roomserver_previous_events WHERE event_nids && ANY(" +
+	"	SELECT ARRAY_AGG(event_nid) FROM roomserver_events WHERE room_nid = $1" +
+	")"
+
+const purgePublishedSQL = "" +
+	"DELETE FROM roomserver_published WHERE room_id = $1"
+
+const purgeRedactionsSQL = "" +
+	"DELETE FROM roomserver_redactions WHERE redaction_event_id = ANY(" +
+	"	SELECT event_id FROM roomserver_events WHERE room_nid = $1" +
+	")"
+
+const purgeRoomAliasesSQL = "" +
+	"DELETE FROM roomserver_room_aliases WHERE room_id = $1"
+
+const purgeRoomSQL = "" +
+	"DELETE FROM roomserver_rooms WHERE room_nid = $1"
+
+const purgeStateBlockEntriesSQL = "" +
+	"DELETE FROM roomserver_state_block WHERE state_block_nid = ANY(" +
+	"	SELECT DISTINCT UNNEST(state_block_nids) FROM roomserver_state_snapshots WHERE room_nid = $1" +
+	")"
+
+const purgeStateSnapshotEntriesSQL = "" +
+	"DELETE FROM roomserver_state_snapshots WHERE room_nid = $1"
+
+type purgeStatements struct {
+	purgeEventJSONStmt            *sql.Stmt
+	purgeEventsStmt               *sql.Stmt
+	purgeInvitesStmt              *sql.Stmt
+	purgeMembershipsStmt          *sql.Stmt
+	purgePreviousEventsStmt       *sql.Stmt
+	purgePublishedStmt            *sql.Stmt
+	purgeRedactionStmt            *sql.Stmt
+	purgeRoomAliasesStmt          *sql.Stmt
+	purgeRoomStmt                 *sql.Stmt
+	purgeStateBlockEntriesStmt    *sql.Stmt
+	purgeStateSnapshotEntriesStmt *sql.Stmt
+}
+
+func PreparePurgeStatements(db *sql.DB) (*purgeStatements, error) {
+	s := &purgeStatements{}
+
+	return s, sqlutil.StatementList{
+		{&s.purgeEventJSONStmt, purgeEventJSONSQL},
+		{&s.purgeEventsStmt, purgeEventsSQL},
+		{&s.purgeInvitesStmt, purgeInvitesSQL},
+		{&s.purgeMembershipsStmt, purgeMembershipsSQL},
+		{&s.purgePublishedStmt, purgePublishedSQL},
+		{&s.purgePreviousEventsStmt, purgePreviousEventsSQL},
+		{&s.purgeRedactionStmt, purgeRedactionsSQL},
+		{&s.purgeRoomAliasesStmt, purgeRoomAliasesSQL},
+		{&s.purgeRoomStmt, purgeRoomSQL},
+		{&s.purgeStateBlockEntriesStmt, purgeStateBlockEntriesSQL},
+		{&s.purgeStateSnapshotEntriesStmt, purgeStateSnapshotEntriesSQL},
+	}.Prepare(db)
+}
+
+func (s *purgeStatements) PurgeRoom(
+	ctx context.Context, txn *sql.Tx, roomNID types.RoomNID, roomID string,
+) error {
+
+	// purge by roomID
+	purgeByRoomID := []*sql.Stmt{
+		s.purgeRoomAliasesStmt,
+		s.purgePublishedStmt,
+	}
+	for _, stmt := range purgeByRoomID {
+		_, err := sqlutil.TxStmt(txn, stmt).ExecContext(ctx, roomID)
+		if err != nil {
+			return err
+		}
+	}
+
+	// purge by roomNID
+	purgeByRoomNID := []*sql.Stmt{
+		s.purgeStateBlockEntriesStmt,
+		s.purgeStateSnapshotEntriesStmt,
+		s.purgeInvitesStmt,
+		s.purgeMembershipsStmt,
+		s.purgePreviousEventsStmt,
+		s.purgeEventJSONStmt,
+		s.purgeRedactionStmt,
+		s.purgeEventsStmt,
+		s.purgeRoomStmt,
+	}
+	for _, stmt := range purgeByRoomNID {
+		_, err := sqlutil.TxStmt(txn, stmt).ExecContext(ctx, roomNID)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/roomserver/storage/postgres/rooms_table.go b/roomserver/storage/postgres/rooms_table.go
index 99439953..c8346733 100644
--- a/roomserver/storage/postgres/rooms_table.go
+++ b/roomserver/storage/postgres/rooms_table.go
@@ -58,6 +58,9 @@ const insertRoomNIDSQL = "" +
 const selectRoomNIDSQL = "" +
 	"SELECT room_nid FROM roomserver_rooms WHERE room_id = $1"
 
+const selectRoomNIDForUpdateSQL = "" +
+	"SELECT room_nid FROM roomserver_rooms WHERE room_id = $1 FOR UPDATE"
+
 const selectLatestEventNIDsSQL = "" +
 	"SELECT latest_event_nids, state_snapshot_nid FROM roomserver_rooms WHERE room_nid = $1"
 
@@ -85,6 +88,7 @@ const bulkSelectRoomNIDsSQL = "" +
 type roomStatements struct {
 	insertRoomNIDStmt                  *sql.Stmt
 	selectRoomNIDStmt                  *sql.Stmt
+	selectRoomNIDForUpdateStmt         *sql.Stmt
 	selectLatestEventNIDsStmt          *sql.Stmt
 	selectLatestEventNIDsForUpdateStmt *sql.Stmt
 	updateLatestEventNIDsStmt          *sql.Stmt
@@ -106,6 +110,7 @@ func PrepareRoomsTable(db *sql.DB) (tables.Rooms, error) {
 	return s, sqlutil.StatementList{
 		{&s.insertRoomNIDStmt, insertRoomNIDSQL},
 		{&s.selectRoomNIDStmt, selectRoomNIDSQL},
+		{&s.selectRoomNIDForUpdateStmt, selectRoomNIDForUpdateSQL},
 		{&s.selectLatestEventNIDsStmt, selectLatestEventNIDsSQL},
 		{&s.selectLatestEventNIDsForUpdateStmt, selectLatestEventNIDsForUpdateSQL},
 		{&s.updateLatestEventNIDsStmt, updateLatestEventNIDsSQL},
@@ -169,6 +174,15 @@ func (s *roomStatements) SelectRoomNID(
 	return types.RoomNID(roomNID), err
 }
 
+func (s *roomStatements) SelectRoomNIDForUpdate(
+	ctx context.Context, txn *sql.Tx, roomID string,
+) (types.RoomNID, error) {
+	var roomNID int64
+	stmt := sqlutil.TxStmt(txn, s.selectRoomNIDForUpdateStmt)
+	err := stmt.QueryRowContext(ctx, roomID).Scan(&roomNID)
+	return types.RoomNID(roomNID), err
+}
+
 func (s *roomStatements) SelectLatestEventNIDs(
 	ctx context.Context, txn *sql.Tx, roomNID types.RoomNID,
 ) ([]types.EventNID, types.StateSnapshotNID, error) {
diff --git a/roomserver/storage/postgres/storage.go b/roomserver/storage/postgres/storage.go
index 23a5f79e..87208438 100644
--- a/roomserver/storage/postgres/storage.go
+++ b/roomserver/storage/postgres/storage.go
@@ -189,6 +189,10 @@ func (d *Database) prepare(db *sql.DB, writer sqlutil.Writer, cache caching.Room
 	if err != nil {
 		return err
 	}
+	purge, err := PreparePurgeStatements(db)
+	if err != nil {
+		return err
+	}
 	d.Database = shared.Database{
 		DB:                  db,
 		Cache:               cache,
@@ -206,6 +210,7 @@ func (d *Database) prepare(db *sql.DB, writer sqlutil.Writer, cache caching.Room
 		MembershipTable:     membership,
 		PublishedTable:      published,
 		RedactionsTable:     redactions,
+		Purge:               purge,
 	}
 	return nil
 }
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index 725cc5bc..654b078d 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -43,6 +43,7 @@ type Database struct {
 	MembershipTable     tables.Membership
 	PublishedTable      tables.Published
 	RedactionsTable     tables.Redactions
+	Purge               tables.Purge
 	GetRoomUpdaterFn    func(ctx context.Context, roomInfo *types.RoomInfo) (*RoomUpdater, error)
 }
 
@@ -1445,6 +1446,21 @@ func (d *Database) ForgetRoom(ctx context.Context, userID, roomID string, forget
 	})
 }
 
+// PurgeRoom removes all information about a given room from the roomserver.
+// For large rooms this operation may take a considerable amount of time.
+func (d *Database) PurgeRoom(ctx context.Context, roomID string) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		roomNID, err := d.RoomsTable.SelectRoomNIDForUpdate(ctx, txn, roomID)
+		if err != nil {
+			if err == sql.ErrNoRows {
+				return fmt.Errorf("room %s does not exist", roomID)
+			}
+			return fmt.Errorf("failed to lock the room: %w", err)
+		}
+		return d.Purge.PurgeRoom(ctx, txn, roomNID, roomID)
+	})
+}
+
 func (d *Database) UpgradeRoom(ctx context.Context, oldRoomID, newRoomID, eventSender string) error {
 
 	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
diff --git a/roomserver/storage/sqlite3/purge_statements.go b/roomserver/storage/sqlite3/purge_statements.go
new file mode 100644
index 00000000..c7b4d27a
--- /dev/null
+++ b/roomserver/storage/sqlite3/purge_statements.go
@@ -0,0 +1,153 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/types"
+)
+
+const purgeEventJSONSQL = "" +
+	"DELETE FROM roomserver_event_json WHERE event_nid IN (" +
+	"	SELECT event_nid FROM roomserver_events WHERE room_nid = $1" +
+	")"
+
+const purgeEventsSQL = "" +
+	"DELETE FROM roomserver_events WHERE room_nid = $1"
+
+const purgeInvitesSQL = "" +
+	"DELETE FROM roomserver_invites WHERE room_nid = $1"
+
+const purgeMembershipsSQL = "" +
+	"DELETE FROM roomserver_membership WHERE room_nid = $1"
+
+const purgePreviousEventsSQL = "" +
+	"DELETE FROM roomserver_previous_events WHERE event_nids IN(" +
+	"	SELECT event_nid FROM roomserver_events WHERE room_nid = $1" +
+	")"
+
+const purgePublishedSQL = "" +
+	"DELETE FROM roomserver_published WHERE room_id = $1"
+
+const purgeRedactionsSQL = "" +
+	"DELETE FROM roomserver_redactions WHERE redaction_event_id IN(" +
+	"	SELECT event_id FROM roomserver_events WHERE room_nid = $1" +
+	")"
+
+const purgeRoomAliasesSQL = "" +
+	"DELETE FROM roomserver_room_aliases WHERE room_id = $1"
+
+const purgeRoomSQL = "" +
+	"DELETE FROM roomserver_rooms WHERE room_nid = $1"
+
+const purgeStateSnapshotEntriesSQL = "" +
+	"DELETE FROM roomserver_state_snapshots WHERE room_nid = $1"
+
+type purgeStatements struct {
+	purgeEventJSONStmt            *sql.Stmt
+	purgeEventsStmt               *sql.Stmt
+	purgeInvitesStmt              *sql.Stmt
+	purgeMembershipsStmt          *sql.Stmt
+	purgePreviousEventsStmt       *sql.Stmt
+	purgePublishedStmt            *sql.Stmt
+	purgeRedactionStmt            *sql.Stmt
+	purgeRoomAliasesStmt          *sql.Stmt
+	purgeRoomStmt                 *sql.Stmt
+	purgeStateSnapshotEntriesStmt *sql.Stmt
+	stateSnapshot                 *stateSnapshotStatements
+}
+
+func PreparePurgeStatements(db *sql.DB, stateSnapshot *stateSnapshotStatements) (*purgeStatements, error) {
+	s := &purgeStatements{stateSnapshot: stateSnapshot}
+	return s, sqlutil.StatementList{
+		{&s.purgeEventJSONStmt, purgeEventJSONSQL},
+		{&s.purgeEventsStmt, purgeEventsSQL},
+		{&s.purgeInvitesStmt, purgeInvitesSQL},
+		{&s.purgeMembershipsStmt, purgeMembershipsSQL},
+		{&s.purgePublishedStmt, purgePublishedSQL},
+		{&s.purgePreviousEventsStmt, purgePreviousEventsSQL},
+		{&s.purgeRedactionStmt, purgeRedactionsSQL},
+		{&s.purgeRoomAliasesStmt, purgeRoomAliasesSQL},
+		{&s.purgeRoomStmt, purgeRoomSQL},
+		//{&s.purgeStateBlockEntriesStmt, purgeStateBlockEntriesSQL},
+		{&s.purgeStateSnapshotEntriesStmt, purgeStateSnapshotEntriesSQL},
+	}.Prepare(db)
+}
+
+func (s *purgeStatements) PurgeRoom(
+	ctx context.Context, txn *sql.Tx, roomNID types.RoomNID, roomID string,
+) error {
+
+	// purge by roomID
+	purgeByRoomID := []*sql.Stmt{
+		s.purgeRoomAliasesStmt,
+		s.purgePublishedStmt,
+	}
+	for _, stmt := range purgeByRoomID {
+		_, err := sqlutil.TxStmt(txn, stmt).ExecContext(ctx, roomID)
+		if err != nil {
+			return err
+		}
+	}
+
+	// purge by roomNID
+	if err := s.purgeStateBlocks(ctx, txn, roomNID); err != nil {
+		return err
+	}
+
+	purgeByRoomNID := []*sql.Stmt{
+		s.purgeStateSnapshotEntriesStmt,
+		s.purgeInvitesStmt,
+		s.purgeMembershipsStmt,
+		s.purgePreviousEventsStmt,
+		s.purgeEventJSONStmt,
+		s.purgeRedactionStmt,
+		s.purgeEventsStmt,
+		s.purgeRoomStmt,
+	}
+	for _, stmt := range purgeByRoomNID {
+		_, err := sqlutil.TxStmt(txn, stmt).ExecContext(ctx, roomNID)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (s *purgeStatements) purgeStateBlocks(
+	ctx context.Context, txn *sql.Tx, roomNID types.RoomNID,
+) error {
+	// Get all stateBlockNIDs
+	stateBlockNIDs, err := s.stateSnapshot.selectStateBlockNIDsForRoomNID(ctx, txn, roomNID)
+	if err != nil {
+		return err
+	}
+	params := make([]interface{}, len(stateBlockNIDs))
+	seenNIDs := make(map[types.StateBlockNID]struct{}, len(stateBlockNIDs))
+	// dedupe NIDs
+	for k, v := range stateBlockNIDs {
+		if _, ok := seenNIDs[v]; ok {
+			continue
+		}
+		params[k] = v
+		seenNIDs[v] = struct{}{}
+	}
+
+	query := "DELETE FROM roomserver_state_block WHERE state_block_nid IN($1)"
+	return sqlutil.RunLimitedVariablesExec(ctx, query, txn, params, sqlutil.SQLite3MaxVariables)
+}
diff --git a/roomserver/storage/sqlite3/rooms_table.go b/roomserver/storage/sqlite3/rooms_table.go
index 25b611b3..7556b346 100644
--- a/roomserver/storage/sqlite3/rooms_table.go
+++ b/roomserver/storage/sqlite3/rooms_table.go
@@ -74,10 +74,14 @@ const bulkSelectRoomIDsSQL = "" +
 const bulkSelectRoomNIDsSQL = "" +
 	"SELECT room_nid FROM roomserver_rooms WHERE room_id IN ($1)"
 
+const selectRoomNIDForUpdateSQL = "" +
+	"SELECT room_nid FROM roomserver_rooms WHERE room_id = $1"
+
 type roomStatements struct {
 	db                                 *sql.DB
 	insertRoomNIDStmt                  *sql.Stmt
 	selectRoomNIDStmt                  *sql.Stmt
+	selectRoomNIDForUpdateStmt         *sql.Stmt
 	selectLatestEventNIDsStmt          *sql.Stmt
 	selectLatestEventNIDsForUpdateStmt *sql.Stmt
 	updateLatestEventNIDsStmt          *sql.Stmt
@@ -105,6 +109,7 @@ func PrepareRoomsTable(db *sql.DB) (tables.Rooms, error) {
 		//{&s.selectRoomVersionForRoomNIDsStmt, selectRoomVersionForRoomNIDsSQL},
 		{&s.selectRoomInfoStmt, selectRoomInfoSQL},
 		{&s.selectRoomIDsStmt, selectRoomIDsSQL},
+		{&s.selectRoomNIDForUpdateStmt, selectRoomNIDForUpdateSQL},
 	}.Prepare(db)
 }
 
@@ -169,6 +174,15 @@ func (s *roomStatements) SelectRoomNID(
 	return types.RoomNID(roomNID), err
 }
 
+func (s *roomStatements) SelectRoomNIDForUpdate(
+	ctx context.Context, txn *sql.Tx, roomID string,
+) (types.RoomNID, error) {
+	var roomNID int64
+	stmt := sqlutil.TxStmt(txn, s.selectRoomNIDForUpdateStmt)
+	err := stmt.QueryRowContext(ctx, roomID).Scan(&roomNID)
+	return types.RoomNID(roomNID), err
+}
+
 func (s *roomStatements) SelectLatestEventNIDs(
 	ctx context.Context, txn *sql.Tx, roomNID types.RoomNID,
 ) ([]types.EventNID, types.StateSnapshotNID, error) {
diff --git a/roomserver/storage/sqlite3/state_block_table.go b/roomserver/storage/sqlite3/state_block_table.go
index 4e67d4da..ae8181cf 100644
--- a/roomserver/storage/sqlite3/state_block_table.go
+++ b/roomserver/storage/sqlite3/state_block_table.go
@@ -24,7 +24,6 @@ import (
 
 	"github.com/matrix-org/dendrite/internal"
 	"github.com/matrix-org/dendrite/internal/sqlutil"
-	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/util"
 )
@@ -68,7 +67,7 @@ func CreateStateBlockTable(db *sql.DB) error {
 	return err
 }
 
-func PrepareStateBlockTable(db *sql.DB) (tables.StateBlock, error) {
+func PrepareStateBlockTable(db *sql.DB) (*stateBlockStatements, error) {
 	s := &stateBlockStatements{
 		db: db,
 	}
diff --git a/roomserver/storage/sqlite3/state_snapshot_table.go b/roomserver/storage/sqlite3/state_snapshot_table.go
index 73827522..930ad14d 100644
--- a/roomserver/storage/sqlite3/state_snapshot_table.go
+++ b/roomserver/storage/sqlite3/state_snapshot_table.go
@@ -62,10 +62,14 @@ const bulkSelectStateBlockNIDsSQL = "" +
 	"SELECT state_snapshot_nid, state_block_nids FROM roomserver_state_snapshots" +
 	" WHERE state_snapshot_nid IN ($1) ORDER BY state_snapshot_nid ASC"
 
+const selectStateBlockNIDsForRoomNID = "" +
+	"SELECT state_block_nids FROM roomserver_state_snapshots WHERE room_nid = $1"
+
 type stateSnapshotStatements struct {
 	db                           *sql.DB
 	insertStateStmt              *sql.Stmt
 	bulkSelectStateBlockNIDsStmt *sql.Stmt
+	selectStateBlockNIDsStmt     *sql.Stmt
 }
 
 func CreateStateSnapshotTable(db *sql.DB) error {
@@ -73,7 +77,7 @@ func CreateStateSnapshotTable(db *sql.DB) error {
 	return err
 }
 
-func PrepareStateSnapshotTable(db *sql.DB) (tables.StateSnapshot, error) {
+func PrepareStateSnapshotTable(db *sql.DB) (*stateSnapshotStatements, error) {
 	s := &stateSnapshotStatements{
 		db: db,
 	}
@@ -81,6 +85,7 @@ func PrepareStateSnapshotTable(db *sql.DB) (tables.StateSnapshot, error) {
 	return s, sqlutil.StatementList{
 		{&s.insertStateStmt, insertStateSQL},
 		{&s.bulkSelectStateBlockNIDsStmt, bulkSelectStateBlockNIDsSQL},
+		{&s.selectStateBlockNIDsStmt, selectStateBlockNIDsForRoomNID},
 	}.Prepare(db)
 }
 
@@ -146,3 +151,29 @@ func (s *stateSnapshotStatements) BulkSelectStateForHistoryVisibility(
 ) ([]types.EventNID, error) {
 	return nil, tables.OptimisationNotSupportedError
 }
+
+func (s *stateSnapshotStatements) selectStateBlockNIDsForRoomNID(
+	ctx context.Context, txn *sql.Tx, roomNID types.RoomNID,
+) ([]types.StateBlockNID, error) {
+	var res []types.StateBlockNID
+	rows, err := sqlutil.TxStmt(txn, s.selectStateBlockNIDsStmt).QueryContext(ctx, roomNID)
+	if err != nil {
+		return res, nil
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectStateBlockNIDsForRoomNID: rows.close() failed")
+
+	var stateBlockNIDs []types.StateBlockNID
+	var stateBlockNIDsJSON string
+	for rows.Next() {
+		if err = rows.Scan(&stateBlockNIDsJSON); err != nil {
+			return nil, err
+		}
+		if err = json.Unmarshal([]byte(stateBlockNIDsJSON), &stateBlockNIDs); err != nil {
+			return nil, err
+		}
+
+		res = append(res, stateBlockNIDs...)
+	}
+
+	return res, rows.Err()
+}
diff --git a/roomserver/storage/sqlite3/storage.go b/roomserver/storage/sqlite3/storage.go
index 01c3f879..392edd28 100644
--- a/roomserver/storage/sqlite3/storage.go
+++ b/roomserver/storage/sqlite3/storage.go
@@ -197,6 +197,11 @@ func (d *Database) prepare(db *sql.DB, writer sqlutil.Writer, cache caching.Room
 	if err != nil {
 		return err
 	}
+	purge, err := PreparePurgeStatements(db, stateSnapshot)
+	if err != nil {
+		return err
+	}
+
 	d.Database = shared.Database{
 		DB:                  db,
 		Cache:               cache,
@@ -215,6 +220,7 @@ func (d *Database) prepare(db *sql.DB, writer sqlutil.Writer, cache caching.Room
 		PublishedTable:      published,
 		RedactionsTable:     redactions,
 		GetRoomUpdaterFn:    d.GetRoomUpdater,
+		Purge:               purge,
 	}
 	return nil
 }
diff --git a/roomserver/storage/tables/interface.go b/roomserver/storage/tables/interface.go
index 80fcf72d..64145f83 100644
--- a/roomserver/storage/tables/interface.go
+++ b/roomserver/storage/tables/interface.go
@@ -73,6 +73,7 @@ type Events interface {
 type Rooms interface {
 	InsertRoomNID(ctx context.Context, txn *sql.Tx, roomID string, roomVersion gomatrixserverlib.RoomVersion) (types.RoomNID, error)
 	SelectRoomNID(ctx context.Context, txn *sql.Tx, roomID string) (types.RoomNID, error)
+	SelectRoomNIDForUpdate(ctx context.Context, txn *sql.Tx, roomID string) (types.RoomNID, error)
 	SelectLatestEventNIDs(ctx context.Context, txn *sql.Tx, roomNID types.RoomNID) ([]types.EventNID, types.StateSnapshotNID, error)
 	SelectLatestEventsNIDsForUpdate(ctx context.Context, txn *sql.Tx, roomNID types.RoomNID) ([]types.EventNID, types.EventNID, types.StateSnapshotNID, error)
 	UpdateLatestEventNIDs(ctx context.Context, txn *sql.Tx, roomNID types.RoomNID, eventNIDs []types.EventNID, lastEventSentNID types.EventNID, stateSnapshotNID types.StateSnapshotNID) error
@@ -173,6 +174,12 @@ type Redactions interface {
 	MarkRedactionValidated(ctx context.Context, txn *sql.Tx, redactionEventID string, validated bool) error
 }
 
+type Purge interface {
+	PurgeRoom(
+		ctx context.Context, txn *sql.Tx, roomNID types.RoomNID, roomID string,
+	) error
+}
+
 // StrippedEvent represents a stripped event for returning extracted content values.
 type StrippedEvent struct {
 	RoomID       string