Drop `reference_sha` column (#3083)

Companion PR to https://github.com/matrix-org/gomatrixserverlib/pull/383

29 files changed, 299 insertions, 227 deletions

diff --git a/.gitignore b/.gitignore
index dcfbf800..043956ee 100644
--- a/.gitignore
+++ b/.gitignore
@@ -74,4 +74,7 @@ complement/
 docs/_site
 
 media_store/
-build
\ No newline at end of file
+build
+
+# golang workspaces
+go.work*
\ No newline at end of file
diff --git a/build/gobind-pinecone/monolith_test.go b/build/gobind-pinecone/monolith_test.go
index 7a7e36c7..f16d1d76 100644
--- a/build/gobind-pinecone/monolith_test.go
+++ b/build/gobind-pinecone/monolith_test.go
@@ -22,7 +22,10 @@ import (
 )
 
 func TestMonolithStarts(t *testing.T) {
-	monolith := DendriteMonolith{}
+	monolith := DendriteMonolith{
+		StorageDirectory: t.TempDir(),
+		CacheDirectory:   t.TempDir(),
+	}
 	monolith.Start()
 	monolith.PublicKey()
 	monolith.Stop()
@@ -60,7 +63,10 @@ func TestMonolithSetRelayServers(t *testing.T) {
 	}
 
 	for _, tc := range testCases {
-		monolith := DendriteMonolith{}
+		monolith := DendriteMonolith{
+			StorageDirectory: t.TempDir(),
+			CacheDirectory:   t.TempDir(),
+		}
 		monolith.Start()
 
 		inputRelays := tc.relays
diff --git a/clientapi/routing/createroom.go b/clientapi/routing/createroom.go
index bc960006..7a7a85e8 100644
--- a/clientapi/routing/createroom.go
+++ b/clientapi/routing/createroom.go
@@ -470,7 +470,7 @@ func createRoom(
 			}
 		}
 		if i > 0 {
-			builder.PrevEvents = []gomatrixserverlib.EventReference{builtEvents[i-1].EventReference()}
+			builder.PrevEvents = []string{builtEvents[i-1].EventID()}
 		}
 		var ev gomatrixserverlib.PDU
 		if err = builder.AddAuthEvents(&authEvents); err != nil {
diff --git a/go.mod b/go.mod
index bf2dc5de..16e5adc8 100644
--- a/go.mod
+++ b/go.mod
@@ -22,7 +22,7 @@ require (
 	github.com/matrix-org/dugong v0.0.0-20210921133753-66e6b1c67e2e
 	github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91
 	github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20230523164045-3fddabebb511
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20230524095531-95ba6c68efb6
 	github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a
 	github.com/matrix-org/util v0.0.0-20221111132719-399730281e66
 	github.com/mattn/go-sqlite3 v1.14.16
diff --git a/go.sum b/go.sum
index 574a7bd7..98e7e839 100644
--- a/go.sum
+++ b/go.sum
@@ -323,8 +323,8 @@ github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91 h1:s7fexw
 github.com/matrix-org/go-sqlite3-js v0.0.0-20220419092513-28aa791a1c91/go.mod h1:e+cg2q7C7yE5QnAXgzo512tgFh1RbQLC0+jozuegKgo=
 github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530 h1:kHKxCOLcHH8r4Fzarl4+Y3K5hjothkVW5z7T1dUM11U=
 github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530/go.mod h1:/gBX06Kw0exX1HrwmoBibFA98yBk/jxKpGVeyQbff+s=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20230523164045-3fddabebb511 h1:om6z/WEVZMxZfgtiyfp5r5ubAObGMyRrnlVD07gIRY4=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20230523164045-3fddabebb511/go.mod h1:H9V9N3Uqn1bBJqYJNGK1noqtgJTaCEhtTdcH/mp50uU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230524095531-95ba6c68efb6 h1:FQpdh/KGCCQJytz4GAdG6pbx3DJ1HNzdKFc/BCZ0hP0=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20230524095531-95ba6c68efb6/go.mod h1:H9V9N3Uqn1bBJqYJNGK1noqtgJTaCEhtTdcH/mp50uU=
 github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a h1:awrPDf9LEFySxTLKYBMCiObelNx/cBuv/wzllvCCH3A=
 github.com/matrix-org/pinecone v0.11.1-0.20230210171230-8c3b24f2649a/go.mod h1:HchJX9oKMXaT2xYFs0Ha/6Zs06mxLU8k6F1ODnrGkeQ=
 github.com/matrix-org/util v0.0.0-20221111132719-399730281e66 h1:6z4KxomXSIGWqhHcfzExgkH3Z3UkIXry4ibJS4Aqz2Y=
diff --git a/internal/eventutil/events.go b/internal/eventutil/events.go
index 79882d8d..ca052c31 100644
--- a/internal/eventutil/events.go
+++ b/internal/eventutil/events.go
@@ -129,18 +129,12 @@ func addPrevEventsToEvent(
 		return ErrRoomNoExists{}
 	}
 
-	verImpl, err := gomatrixserverlib.GetRoomVersion(queryRes.RoomVersion)
-	if err != nil {
-		return fmt.Errorf("GetRoomVersion: %w", err)
-	}
-	eventFormat := verImpl.EventFormat()
-
 	builder.Depth = queryRes.Depth
 
 	authEvents := gomatrixserverlib.NewAuthEvents(nil)
 
 	for i := range queryRes.StateEvents {
-		err = authEvents.AddEvent(queryRes.StateEvents[i].PDU)
+		err := authEvents.AddEvent(queryRes.StateEvents[i].PDU)
 		if err != nil {
 			return fmt.Errorf("authEvents.AddEvent: %w", err)
 		}
@@ -151,22 +145,7 @@ func addPrevEventsToEvent(
 		return fmt.Errorf("eventsNeeded.AuthEventReferences: %w", err)
 	}
 
-	truncAuth, truncPrev := truncateAuthAndPrevEvents(refs, queryRes.LatestEvents)
-	switch eventFormat {
-	case gomatrixserverlib.EventFormatV1:
-		builder.AuthEvents = truncAuth
-		builder.PrevEvents = truncPrev
-	case gomatrixserverlib.EventFormatV2:
-		v2AuthRefs, v2PrevRefs := []string{}, []string{}
-		for _, ref := range truncAuth {
-			v2AuthRefs = append(v2AuthRefs, ref.EventID)
-		}
-		for _, ref := range truncPrev {
-			v2PrevRefs = append(v2PrevRefs, ref.EventID)
-		}
-		builder.AuthEvents = v2AuthRefs
-		builder.PrevEvents = v2PrevRefs
-	}
+	builder.AuthEvents, builder.PrevEvents = truncateAuthAndPrevEvents(refs, queryRes.LatestEvents)
 
 	return nil
 }
@@ -176,8 +155,8 @@ func addPrevEventsToEvent(
 // NOTSPEC: The limits here feel a bit arbitrary but they are currently
 // here because of https://github.com/matrix-org/matrix-doc/issues/2307
 // and because Synapse will just drop events that don't comply.
-func truncateAuthAndPrevEvents(auth, prev []gomatrixserverlib.EventReference) (
-	truncAuth, truncPrev []gomatrixserverlib.EventReference,
+func truncateAuthAndPrevEvents(auth, prev []string) (
+	truncAuth, truncPrev []string,
 ) {
 	truncAuth, truncPrev = auth, prev
 	if len(truncAuth) > 10 {
diff --git a/roomserver/api/query.go b/roomserver/api/query.go
index 55d1a6db..1726bfe1 100644
--- a/roomserver/api/query.go
+++ b/roomserver/api/query.go
@@ -49,7 +49,7 @@ type QueryLatestEventsAndStateResponse struct {
 	RoomVersion gomatrixserverlib.RoomVersion `json:"room_version"`
 	// The latest events in the room.
 	// These are used to set the prev_events when sending an event.
-	LatestEvents []gomatrixserverlib.EventReference `json:"latest_events"`
+	LatestEvents []string `json:"latest_events"`
 	// The state events requested.
 	// This list will be in an arbitrary order.
 	// These are used to set the auth_events when sending an event.
diff --git a/roomserver/internal/input/input_events.go b/roomserver/internal/input/input_events.go
index cd78b372..02a1a280 100644
--- a/roomserver/internal/input/input_events.go
+++ b/roomserver/internal/input/input_events.go
@@ -883,9 +883,7 @@ func (r *Inputer) kickGuests(ctx context.Context, event gomatrixserverlib.PDU, r
 			Origin:       senderDomain,
 			SendAsServer: string(senderDomain),
 		})
-		prevEvents = []gomatrixserverlib.EventReference{
-			event.EventReference(),
-		}
+		prevEvents = []string{event.EventID()}
 	}
 
 	inputReq := &api.InputRoomEventsRequest{
diff --git a/roomserver/internal/input/input_latest_events.go b/roomserver/internal/input/input_latest_events.go
index 54a5f623..7a7a021a 100644
--- a/roomserver/internal/input/input_latest_events.go
+++ b/roomserver/internal/input/input_latest_events.go
@@ -154,8 +154,8 @@ func (u *latestEventsUpdater) doUpdateLatestEvents() error {
 	extremitiesChanged, err := u.calculateLatest(
 		u.oldLatest, u.event,
 		types.StateAtEventAndReference{
-			EventReference: u.event.EventReference(),
-			StateAtEvent:   u.stateAtEvent,
+			EventID:      u.event.EventID(),
+			StateAtEvent: u.stateAtEvent,
 		},
 	)
 	if err != nil {
@@ -349,7 +349,7 @@ func (u *latestEventsUpdater) calculateLatest(
 	// If the "new" event is already referenced by an existing event
 	// then do nothing - it's not a candidate to be a new extremity if
 	// it has been referenced.
-	if referenced, err := u.updater.IsReferenced(newEvent.EventReference()); err != nil {
+	if referenced, err := u.updater.IsReferenced(newEvent.EventID()); err != nil {
 		return false, fmt.Errorf("u.updater.IsReferenced(new): %w", err)
 	} else if referenced {
 		u.latest = oldLatest
@@ -360,7 +360,7 @@ func (u *latestEventsUpdater) calculateLatest(
 	// have entries in the previous events table. If they do then we
 	// will no longer include them as forward extremities.
 	for k, l := range existingRefs {
-		referenced, err := u.updater.IsReferenced(l.EventReference)
+		referenced, err := u.updater.IsReferenced(l.EventID)
 		if err != nil {
 			return false, fmt.Errorf("u.updater.IsReferenced: %w", err)
 		} else if referenced {
diff --git a/roomserver/internal/input/input_missing.go b/roomserver/internal/input/input_missing.go
index 8a123522..10486138 100644
--- a/roomserver/internal/input/input_missing.go
+++ b/roomserver/internal/input/input_missing.go
@@ -520,9 +520,9 @@ func (t *missingStateReq) getMissingEvents(ctx context.Context, e gomatrixserver
 		return nil, false, false, fmt.Errorf("t.DB.LatestEventIDs: %w", err)
 	}
 	latestEvents := make([]string, len(latest))
-	for i, ev := range latest {
-		latestEvents[i] = ev.EventID
-		t.hadEvent(ev.EventID)
+	for i := range latest {
+		latestEvents[i] = latest[i]
+		t.hadEvent(latest[i])
 	}
 
 	var missingResp *fclient.RespMissingEvents
diff --git a/roomserver/internal/perform/perform_admin.go b/roomserver/internal/perform/perform_admin.go
index fadc8bcf..17296feb 100644
--- a/roomserver/internal/perform/perform_admin.go
+++ b/roomserver/internal/perform/perform_admin.go
@@ -131,9 +131,7 @@ func (r *Admin) PerformAdminEvacuateRoom(
 			SendAsServer: string(senderDomain),
 		})
 		affected = append(affected, stateKey)
-		prevEvents = []gomatrixserverlib.EventReference{
-			event.EventReference(),
-		}
+		prevEvents = []string{event.EventID()}
 	}
 
 	inputReq := &api.InputRoomEventsRequest{
@@ -253,9 +251,9 @@ func (r *Admin) PerformAdminDownloadState(
 
 	for _, fwdExtremity := range fwdExtremities {
 		var state gomatrixserverlib.StateResponse
-		state, err = r.Inputer.FSAPI.LookupState(ctx, r.Inputer.ServerName, serverName, roomID, fwdExtremity.EventID, roomInfo.RoomVersion)
+		state, err = r.Inputer.FSAPI.LookupState(ctx, r.Inputer.ServerName, serverName, roomID, fwdExtremity, roomInfo.RoomVersion)
 		if err != nil {
-			return fmt.Errorf("r.Inputer.FSAPI.LookupState (%q): %s", fwdExtremity.EventID, err)
+			return fmt.Errorf("r.Inputer.FSAPI.LookupState (%q): %s", fwdExtremity, err)
 		}
 		for _, authEvent := range state.GetAuthEvents().UntrustedEvents(roomInfo.RoomVersion) {
 			if err = gomatrixserverlib.VerifyEventSignatures(ctx, authEvent, r.Inputer.KeyRing); err != nil {
diff --git a/roomserver/internal/perform/perform_inbound_peek.go b/roomserver/internal/perform/perform_inbound_peek.go
index 3094a17f..3ac0f6f4 100644
--- a/roomserver/internal/perform/perform_inbound_peek.go
+++ b/roomserver/internal/perform/perform_inbound_peek.go
@@ -64,7 +64,7 @@ func (r *InboundPeeker) PerformInboundPeek(
 	if err != nil {
 		return err
 	}
-	latestEvents, err := r.DB.EventsFromIDs(ctx, info, []string{latestEventRefs[0].EventID})
+	latestEvents, err := r.DB.EventsFromIDs(ctx, info, []string{latestEventRefs[0]})
 	if err != nil {
 		return err
 	}
diff --git a/roomserver/internal/perform/perform_upgrade.go b/roomserver/internal/perform/perform_upgrade.go
index abe63145..60085cb6 100644
--- a/roomserver/internal/perform/perform_upgrade.go
+++ b/roomserver/internal/perform/perform_upgrade.go
@@ -471,7 +471,7 @@ func (r *Upgrader) sendInitialEvents(ctx context.Context, evTime time.Time, user
 			return fmt.Errorf("failed to set content of new %q event: %w", proto.Type, err)
 		}
 		if i > 0 {
-			proto.PrevEvents = []gomatrixserverlib.EventReference{builtEvents[i-1].EventReference()}
+			proto.PrevEvents = []string{builtEvents[i-1].EventID()}
 		}
 
 		var verImpl gomatrixserverlib.IRoomVersion
diff --git a/roomserver/internal/query/query_test.go b/roomserver/internal/query/query_test.go
index b6715cb0..619d9303 100644
--- a/roomserver/internal/query/query_test.go
+++ b/roomserver/internal/query/query_test.go
@@ -43,13 +43,10 @@ func createEventDB() *getEventDB {
 
 // Adds a fake event to the storage with given auth events.
 func (db *getEventDB) addFakeEvent(eventID string, authIDs []string) error {
-	authEvents := []gomatrixserverlib.EventReference{}
+	authEvents := make([]any, 0, len(authIDs))
 	for _, authID := range authIDs {
-		authEvents = append(authEvents, gomatrixserverlib.EventReference{
-			EventID: authID,
-		})
+		authEvents = append(authEvents, []any{authID, struct{}{}})
 	}
-
 	builder := map[string]interface{}{
 		"event_id":    eventID,
 		"auth_events": authEvents,
diff --git a/roomserver/storage/interface.go b/roomserver/storage/interface.go
index 6bc4ce9a..7d22df00 100644
--- a/roomserver/storage/interface.go
+++ b/roomserver/storage/interface.go
@@ -102,7 +102,7 @@ type Database interface {
 	// Look up event references for the latest events in the room and the current state snapshot.
 	// Returns the latest events, the current state and the maximum depth of the latest events plus 1.
 	// Returns an error if there was a problem talking to the database.
-	LatestEventIDs(ctx context.Context, roomNID types.RoomNID) ([]gomatrixserverlib.EventReference, types.StateSnapshotNID, int64, error)
+	LatestEventIDs(ctx context.Context, roomNID types.RoomNID) ([]string, types.StateSnapshotNID, int64, error)
 	// Look up the active invites targeting a user in a room and return the
 	// numeric state key IDs for the user IDs who sent them along with the event IDs for the invites.
 	// Returns an error if there was a problem talking to the database.
@@ -206,7 +206,7 @@ type RoomDatabase interface {
 	BulkSelectSnapshotsFromEventIDs(ctx context.Context, eventIDs []string) (map[types.StateSnapshotNID][]string, error)
 	StateEntriesForTuples(ctx context.Context, stateBlockNIDs []types.StateBlockNID, stateKeyTuples []types.StateKeyTuple) ([]types.StateEntryList, error)
 	AddState(ctx context.Context, roomNID types.RoomNID, stateBlockNIDs []types.StateBlockNID, state []types.StateEntry) (types.StateSnapshotNID, error)
-	LatestEventIDs(ctx context.Context, roomNID types.RoomNID) ([]gomatrixserverlib.EventReference, types.StateSnapshotNID, int64, error)
+	LatestEventIDs(ctx context.Context, roomNID types.RoomNID) ([]string, types.StateSnapshotNID, int64, error)
 	GetOrCreateRoomInfo(ctx context.Context, event gomatrixserverlib.PDU) (*types.RoomInfo, error)
 	GetOrCreateEventTypeNID(ctx context.Context, eventType string) (eventTypeNID types.EventTypeNID, err error)
 	GetOrCreateEventStateKeyNID(ctx context.Context, eventStateKey *string) (types.EventStateKeyNID, error)
diff --git a/roomserver/storage/postgres/deltas/20230516154000_drop_reference_sha.go b/roomserver/storage/postgres/deltas/20230516154000_drop_reference_sha.go
new file mode 100644
index 00000000..c1957771
--- /dev/null
+++ b/roomserver/storage/postgres/deltas/20230516154000_drop_reference_sha.go
@@ -0,0 +1,54 @@
+// Copyright 2023 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 deltas
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+func UpDropEventReferenceSHAEvents(ctx context.Context, tx *sql.Tx) error {
+	var count int
+	err := tx.QueryRowContext(ctx, `SELECT count(*) FROM roomserver_events GROUP BY event_id HAVING count(event_id) > 1`).
+		Scan(&count)
+	if err != nil && err != sql.ErrNoRows {
+		return fmt.Errorf("failed to query duplicate event ids")
+	}
+	if count > 0 {
+		return fmt.Errorf("unable to drop column, as there are duplicate event ids")
+	}
+	_, err = tx.ExecContext(ctx, `ALTER TABLE roomserver_events DROP COLUMN IF EXISTS reference_sha256;`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	return nil
+}
+
+func UpDropEventReferenceSHAPrevEvents(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, "ALTER TABLE roomserver_previous_events DROP CONSTRAINT roomserver_previous_event_id_unique;")
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	_, err = tx.ExecContext(ctx, `ALTER TABLE roomserver_previous_events DROP COLUMN IF EXISTS previous_reference_sha256;`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	_, err = tx.ExecContext(ctx, `ALTER TABLE roomserver_previous_events ADD CONSTRAINT roomserver_previous_event_id_unique UNIQUE (previous_event_id);`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	return nil
+}
diff --git a/roomserver/storage/postgres/events_table.go b/roomserver/storage/postgres/events_table.go
index c935608a..a00b4b1d 100644
--- a/roomserver/storage/postgres/events_table.go
+++ b/roomserver/storage/postgres/events_table.go
@@ -22,10 +22,9 @@ import (
 	"sort"
 
 	"github.com/lib/pq"
-	"github.com/matrix-org/gomatrixserverlib"
-
 	"github.com/matrix-org/dendrite/internal"
 	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/storage/postgres/deltas"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 	"github.com/matrix-org/dendrite/roomserver/types"
 )
@@ -62,9 +61,6 @@ CREATE TABLE IF NOT EXISTS roomserver_events (
     -- Needed for state resolution.
     -- An event may only appear in this table once.
     event_id TEXT NOT NULL CONSTRAINT roomserver_event_id_unique UNIQUE,
-    -- The sha256 reference hash for the event.
-    -- Needed for setting reference hashes when sending new events.
-    reference_sha256 BYTEA NOT NULL,
     -- A list of numeric IDs for events that can authenticate this event.
 	auth_event_nids BIGINT[] NOT NULL,
 	is_rejected BOOLEAN NOT NULL DEFAULT FALSE
@@ -75,10 +71,10 @@ CREATE INDEX IF NOT EXISTS roomserver_events_memberships_idx ON roomserver_event
 `
 
 const insertEventSQL = "" +
-	"INSERT INTO roomserver_events AS e (room_nid, event_type_nid, event_state_key_nid, event_id, reference_sha256, auth_event_nids, depth, is_rejected)" +
-	" VALUES ($1, $2, $3, $4, $5, $6, $7, $8)" +
+	"INSERT INTO roomserver_events AS e (room_nid, event_type_nid, event_state_key_nid, event_id, auth_event_nids, depth, is_rejected)" +
+	" VALUES ($1, $2, $3, $4, $5, $6, $7)" +
 	" ON CONFLICT ON CONSTRAINT roomserver_event_id_unique DO UPDATE" +
-	" SET is_rejected = $8 WHERE e.event_id = $4 AND e.is_rejected = TRUE" +
+	" SET is_rejected = $7 WHERE e.event_id = $4 AND e.is_rejected = TRUE" +
 	" RETURNING event_nid, state_snapshot_nid"
 
 const selectEventSQL = "" +
@@ -130,12 +126,9 @@ const selectEventIDSQL = "" +
 	"SELECT event_id FROM roomserver_events WHERE event_nid = $1"
 
 const bulkSelectStateAtEventAndReferenceSQL = "" +
-	"SELECT event_type_nid, event_state_key_nid, event_nid, state_snapshot_nid, event_id, reference_sha256" +
+	"SELECT event_type_nid, event_state_key_nid, event_nid, state_snapshot_nid, event_id" +
 	" FROM roomserver_events WHERE event_nid = ANY($1)"
 
-const bulkSelectEventReferenceSQL = "" +
-	"SELECT event_id, reference_sha256 FROM roomserver_events WHERE event_nid = ANY($1)"
-
 const bulkSelectEventIDSQL = "" +
 	"SELECT event_nid, event_id FROM roomserver_events WHERE event_nid = ANY($1)"
 
@@ -167,7 +160,6 @@ type eventStatements struct {
 	updateEventSentToOutputStmt                   *sql.Stmt
 	selectEventIDStmt                             *sql.Stmt
 	bulkSelectStateAtEventAndReferenceStmt        *sql.Stmt
-	bulkSelectEventReferenceStmt                  *sql.Stmt
 	bulkSelectEventIDStmt                         *sql.Stmt
 	bulkSelectEventNIDStmt                        *sql.Stmt
 	bulkSelectUnsentEventNIDStmt                  *sql.Stmt
@@ -178,7 +170,18 @@ type eventStatements struct {
 
 func CreateEventsTable(db *sql.DB) error {
 	_, err := db.Exec(eventsSchema)
-	return err
+	if err != nil {
+		return err
+	}
+
+	m := sqlutil.NewMigrator(db)
+	m.AddMigrations([]sqlutil.Migration{
+		{
+			Version: "roomserver: drop column reference_sha from roomserver_events",
+			Up:      deltas.UpDropEventReferenceSHAEvents,
+		},
+	}...)
+	return m.Up(context.Background())
 }
 
 func PrepareEventsTable(db *sql.DB) (tables.Events, error) {
@@ -197,7 +200,6 @@ func PrepareEventsTable(db *sql.DB) (tables.Events, error) {
 		{&s.selectEventSentToOutputStmt, selectEventSentToOutputSQL},
 		{&s.selectEventIDStmt, selectEventIDSQL},
 		{&s.bulkSelectStateAtEventAndReferenceStmt, bulkSelectStateAtEventAndReferenceSQL},
-		{&s.bulkSelectEventReferenceStmt, bulkSelectEventReferenceSQL},
 		{&s.bulkSelectEventIDStmt, bulkSelectEventIDSQL},
 		{&s.bulkSelectEventNIDStmt, bulkSelectEventNIDSQL},
 		{&s.bulkSelectUnsentEventNIDStmt, bulkSelectUnsentEventNIDSQL},
@@ -214,7 +216,6 @@ func (s *eventStatements) InsertEvent(
 	eventTypeNID types.EventTypeNID,
 	eventStateKeyNID types.EventStateKeyNID,
 	eventID string,
-	referenceSHA256 []byte,
 	authEventNIDs []types.EventNID,
 	depth int64,
 	isRejected bool,
@@ -224,7 +225,7 @@ func (s *eventStatements) InsertEvent(
 	stmt := sqlutil.TxStmt(txn, s.insertEventStmt)
 	err := stmt.QueryRowContext(
 		ctx, int64(roomNID), int64(eventTypeNID), int64(eventStateKeyNID),
-		eventID, referenceSHA256, eventNIDsAsArray(authEventNIDs), depth,
+		eventID, eventNIDsAsArray(authEventNIDs), depth,
 		isRejected,
 	).Scan(&eventNID, &stateNID)
 	return types.EventNID(eventNID), types.StateSnapshotNID(stateNID), err
@@ -441,11 +442,10 @@ func (s *eventStatements) BulkSelectStateAtEventAndReference(
 		eventNID         int64
 		stateSnapshotNID int64
 		eventID          string
-		eventSHA256      []byte
 	)
 	for ; rows.Next(); i++ {
 		if err = rows.Scan(
-			&eventTypeNID, &eventStateKeyNID, &eventNID, &stateSnapshotNID, &eventID, &eventSHA256,
+			&eventTypeNID, &eventStateKeyNID, &eventNID, &stateSnapshotNID, &eventID,
 		); err != nil {
 			return nil, err
 		}
@@ -455,32 +455,6 @@ func (s *eventStatements) BulkSelectStateAtEventAndReference(
 		result.EventNID = types.EventNID(eventNID)
 		result.BeforeStateSnapshotNID = types.StateSnapshotNID(stateSnapshotNID)
 		result.EventID = eventID
-		result.EventSHA256 = eventSHA256
-	}
-	if err = rows.Err(); err != nil {
-		return nil, err
-	}
-	if i != len(eventNIDs) {
-		return nil, fmt.Errorf("storage: event NIDs missing from the database (%d != %d)", i, len(eventNIDs))
-	}
-	return results, nil
-}
-
-func (s *eventStatements) BulkSelectEventReference(
-	ctx context.Context, txn *sql.Tx, eventNIDs []types.EventNID,
-) ([]gomatrixserverlib.EventReference, error) {
-	rows, err := s.bulkSelectEventReferenceStmt.QueryContext(ctx, eventNIDsAsArray(eventNIDs))
-	if err != nil {
-		return nil, err
-	}
-	defer internal.CloseAndLogIfError(ctx, rows, "bulkSelectEventReference: rows.close() failed")
-	results := make([]gomatrixserverlib.EventReference, len(eventNIDs))
-	i := 0
-	for ; rows.Next(); i++ {
-		result := &results[i]
-		if err = rows.Scan(&result.EventID, &result.EventSHA256); err != nil {
-			return nil, err
-		}
 	}
 	if err = rows.Err(); err != nil {
 		return nil, err
diff --git a/roomserver/storage/postgres/previous_events_table.go b/roomserver/storage/postgres/previous_events_table.go
index 26999a29..ceb5e26b 100644
--- a/roomserver/storage/postgres/previous_events_table.go
+++ b/roomserver/storage/postgres/previous_events_table.go
@@ -20,6 +20,7 @@ import (
 	"database/sql"
 
 	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/storage/postgres/deltas"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 	"github.com/matrix-org/dendrite/roomserver/types"
 )
@@ -32,11 +33,9 @@ const previousEventSchema = `
 CREATE TABLE IF NOT EXISTS roomserver_previous_events (
     -- The string event ID taken from the prev_events key of an event.
     previous_event_id TEXT NOT NULL,
-    -- The SHA256 reference hash taken from the prev_events key of an event.
-    previous_reference_sha256 BYTEA NOT NULL,
     -- A list of numeric event IDs of events that reference this prev_event.
     event_nids BIGINT[] NOT NULL,
-    CONSTRAINT roomserver_previous_event_id_unique UNIQUE (previous_event_id, previous_reference_sha256)
+    CONSTRAINT roomserver_previous_event_id_unique UNIQUE (previous_event_id)
 );
 `
 
@@ -47,17 +46,17 @@ CREATE TABLE IF NOT EXISTS roomserver_previous_events (
 // The lock is necessary to avoid data races when checking whether an event is already referenced by another event.
 const insertPreviousEventSQL = "" +
 	"INSERT INTO roomserver_previous_events" +
-	" (previous_event_id, previous_reference_sha256, event_nids)" +
-	" VALUES ($1, $2, array_append('{}'::bigint[], $3))" +
+	" (previous_event_id, event_nids)" +
+	" VALUES ($1, array_append('{}'::bigint[], $2))" +
 	" ON CONFLICT ON CONSTRAINT roomserver_previous_event_id_unique" +
-	" DO UPDATE SET event_nids = array_append(roomserver_previous_events.event_nids, $3)" +
-	" WHERE $3 != ALL(roomserver_previous_events.event_nids)"
+	" DO UPDATE SET event_nids = array_append(roomserver_previous_events.event_nids, $2)" +
+	" WHERE $2 != ALL(roomserver_previous_events.event_nids)"
 
 // Check if the event is referenced by another event in the table.
 // This should only be done while holding a "FOR UPDATE" lock on the row in the rooms table for this room.
 const selectPreviousEventExistsSQL = "" +
 	"SELECT 1 FROM roomserver_previous_events" +
-	" WHERE previous_event_id = $1 AND previous_reference_sha256 = $2"
+	" WHERE previous_event_id = $1"
 
 type previousEventStatements struct {
 	insertPreviousEventStmt       *sql.Stmt
@@ -66,7 +65,18 @@ type previousEventStatements struct {
 
 func CreatePrevEventsTable(db *sql.DB) error {
 	_, err := db.Exec(previousEventSchema)
-	return err
+	if err != nil {
+		return err
+	}
+
+	m := sqlutil.NewMigrator(db)
+	m.AddMigrations([]sqlutil.Migration{
+		{
+			Version: "roomserver: drop column reference_sha from roomserver_prev_events",
+			Up:      deltas.UpDropEventReferenceSHAPrevEvents,
+		},
+	}...)
+	return m.Up(context.Background())
 }
 
 func PreparePrevEventsTable(db *sql.DB) (tables.PreviousEvents, error) {
@@ -82,12 +92,11 @@ func (s *previousEventStatements) InsertPreviousEvent(
 	ctx context.Context,
 	txn *sql.Tx,
 	previousEventID string,
-	previousEventReferenceSHA256 []byte,
 	eventNID types.EventNID,
 ) error {
 	stmt := sqlutil.TxStmt(txn, s.insertPreviousEventStmt)
 	_, err := stmt.ExecContext(
-		ctx, previousEventID, previousEventReferenceSHA256, int64(eventNID),
+		ctx, previousEventID, int64(eventNID),
 	)
 	return err
 }
@@ -95,9 +104,9 @@ func (s *previousEventStatements) InsertPreviousEvent(
 // Check if the event reference exists
 // Returns sql.ErrNoRows if the event reference doesn't exist.
 func (s *previousEventStatements) SelectPreviousEventExists(
-	ctx context.Context, txn *sql.Tx, eventID string, eventReferenceSHA256 []byte,
+	ctx context.Context, txn *sql.Tx, eventID string,
 ) error {
 	var ok int64
 	stmt := sqlutil.TxStmt(txn, s.selectPreviousEventExistsStmt)
-	return stmt.QueryRowContext(ctx, eventID, eventReferenceSHA256).Scan(&ok)
+	return stmt.QueryRowContext(ctx, eventID).Scan(&ok)
 }
diff --git a/roomserver/storage/shared/room_updater.go b/roomserver/storage/shared/room_updater.go
index 5a20c67b..70672a33 100644
--- a/roomserver/storage/shared/room_updater.go
+++ b/roomserver/storage/shared/room_updater.go
@@ -104,18 +104,6 @@ func (u *RoomUpdater) CurrentStateSnapshotNID() types.StateSnapshotNID {
 	return u.currentStateSnapshotNID
 }
 
-// StorePreviousEvents implements types.RoomRecentEventsUpdater - This must be called from a Writer
-func (u *RoomUpdater) StorePreviousEvents(eventNID types.EventNID, previousEventReferences []gomatrixserverlib.EventReference) error {
-	return u.d.Writer.Do(u.d.DB, u.txn, func(txn *sql.Tx) error {
-		for _, ref := range previousEventReferences {
-			if err := u.d.PrevEventsTable.InsertPreviousEvent(u.ctx, txn, ref.EventID, ref.EventSHA256, eventNID); err != nil {
-				return fmt.Errorf("u.d.PrevEventsTable.InsertPreviousEvent: %w", err)
-			}
-		}
-		return nil
-	})
-}
-
 func (u *RoomUpdater) Events(ctx context.Context, _ gomatrixserverlib.RoomVersion, eventNIDs []types.EventNID) ([]types.Event, error) {
 	if u.roomInfo == nil {
 		return nil, types.ErrorInvalidRoomInfo
@@ -203,8 +191,8 @@ func (u *RoomUpdater) EventsFromIDs(ctx context.Context, roomInfo *types.RoomInf
 }
 
 // IsReferenced implements types.RoomRecentEventsUpdater
-func (u *RoomUpdater) IsReferenced(eventReference gomatrixserverlib.EventReference) (bool, error) {
-	err := u.d.PrevEventsTable.SelectPreviousEventExists(u.ctx, u.txn, eventReference.EventID, eventReference.EventSHA256)
+func (u *RoomUpdater) IsReferenced(eventID string) (bool, error) {
+	err := u.d.PrevEventsTable.SelectPreviousEventExists(u.ctx, u.txn, eventID)
 	if err == nil {
 		return true, nil
 	}
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index 60e46c47..cefa58a3 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -398,15 +398,13 @@ func (d *EventDatabase) eventsFromIDs(ctx context.Context, txn *sql.Tx, roomInfo
 	return d.events(ctx, txn, roomInfo.RoomVersion, nids)
 }
 
-func (d *Database) LatestEventIDs(
-	ctx context.Context, roomNID types.RoomNID,
-) (references []gomatrixserverlib.EventReference, currentStateSnapshotNID types.StateSnapshotNID, depth int64, err error) {
+func (d *Database) LatestEventIDs(ctx context.Context, roomNID types.RoomNID) (references []string, currentStateSnapshotNID types.StateSnapshotNID, depth int64, err error) {
 	var eventNIDs []types.EventNID
 	eventNIDs, currentStateSnapshotNID, err = d.RoomsTable.SelectLatestEventNIDs(ctx, nil, roomNID)
 	if err != nil {
 		return
 	}
-	references, err = d.EventsTable.BulkSelectEventReference(ctx, nil, eventNIDs)
+	eventNIDMap, err := d.EventsTable.BulkSelectEventID(ctx, nil, eventNIDs)
 	if err != nil {
 		return
 	}
@@ -414,6 +412,9 @@ func (d *Database) LatestEventIDs(
 	if err != nil {
 		return
 	}
+	for _, eventID := range eventNIDMap {
+		references = append(references, eventID)
+	}
 	return
 }
 
@@ -742,7 +743,6 @@ func (d *EventDatabase) StoreEvent(
 			eventTypeNID,
 			eventStateKeyNID,
 			event.EventID(),
-			event.EventReference().EventSHA256,
 			authEventNIDs,
 			event.Depth(),
 			isRejected,
@@ -762,7 +762,7 @@ func (d *EventDatabase) StoreEvent(
 			return fmt.Errorf("d.EventJSONTable.InsertEventJSON: %w", err)
 		}
 
-		if prevEvents := event.PrevEvents(); len(prevEvents) > 0 {
+		if prevEvents := event.PrevEventIDs(); len(prevEvents) > 0 {
 			// Create an updater - NB: on sqlite this WILL create a txn as we are directly calling the shared DB form of
 			// GetLatestEventsForUpdate - not via the SQLiteDatabase form which has `nil` txns. This
 			// function only does SELECTs though so the created txn (at this point) is just a read txn like
@@ -770,8 +770,8 @@ func (d *EventDatabase) StoreEvent(
 			// to do writes however then this will need to go inside `Writer.Do`.
 
 			// The following is a copy of RoomUpdater.StorePreviousEvents
-			for _, ref := range prevEvents {
-				if err = d.PrevEventsTable.InsertPreviousEvent(ctx, txn, ref.EventID, ref.EventSHA256, eventNID); err != nil {
+			for _, eventID := range prevEvents {
+				if err = d.PrevEventsTable.InsertPreviousEvent(ctx, txn, eventID, eventNID); err != nil {
 					return fmt.Errorf("u.d.PrevEventsTable.InsertPreviousEvent: %w", err)
 				}
 			}
diff --git a/roomserver/storage/sqlite3/deltas/20230516154000_drop_reference_sha.go b/roomserver/storage/sqlite3/deltas/20230516154000_drop_reference_sha.go
new file mode 100644
index 00000000..452d72ac
--- /dev/null
+++ b/roomserver/storage/sqlite3/deltas/20230516154000_drop_reference_sha.go
@@ -0,0 +1,72 @@
+// Copyright 2023 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 deltas
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+func UpDropEventReferenceSHA(ctx context.Context, tx *sql.Tx) error {
+	var count int
+	err := tx.QueryRowContext(ctx, `SELECT count(*) FROM roomserver_events GROUP BY event_id HAVING count(event_id) > 1`).
+		Scan(&count)
+	if err != nil && err != sql.ErrNoRows {
+		return fmt.Errorf("failed to query duplicate event ids")
+	}
+	if count > 0 {
+		return fmt.Errorf("unable to drop column, as there are duplicate event ids")
+	}
+	_, err = tx.ExecContext(ctx, `ALTER TABLE roomserver_events DROP COLUMN reference_sha256;`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	return nil
+}
+
+func UpDropEventReferenceSHAPrevEvents(ctx context.Context, tx *sql.Tx) error {
+	// rename the table
+	if _, err := tx.ExecContext(ctx, `ALTER TABLE roomserver_previous_events RENAME TO _roomserver_previous_events;`); err != nil {
+		return fmt.Errorf("tx.ExecContext: %w", err)
+	}
+
+	// create new table
+	if _, err := tx.ExecContext(ctx, `CREATE TABLE IF NOT EXISTS roomserver_previous_events (
+    previous_event_id TEXT NOT NULL,
+    event_nids TEXT NOT NULL,
+    UNIQUE (previous_event_id)
+  );`); err != nil {
+		return fmt.Errorf("tx.ExecContext: %w", err)
+	}
+
+	// move data
+	if _, err := tx.ExecContext(ctx, `
+INSERT
+    INTO roomserver_previous_events (
+      previous_event_id, event_nids
+    ) SELECT
+        previous_event_id, event_nids
+    FROM _roomserver_previous_events
+;`); err != nil {
+		return fmt.Errorf("tx.ExecContext: %w", err)
+	}
+	// drop old table
+	_, err := tx.ExecContext(ctx, `DROP TABLE _roomserver_previous_events;`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	return nil
+}
diff --git a/roomserver/storage/sqlite3/events_table.go b/roomserver/storage/sqlite3/events_table.go
index aacf4bc9..c49c6dc3 100644
--- a/roomserver/storage/sqlite3/events_table.go
+++ b/roomserver/storage/sqlite3/events_table.go
@@ -19,14 +19,14 @@ import (
 	"context"
 	"database/sql"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"sort"
 	"strings"
 
-	"github.com/matrix-org/gomatrixserverlib"
-
 	"github.com/matrix-org/dendrite/internal"
 	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/storage/sqlite3/deltas"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 	"github.com/matrix-org/dendrite/roomserver/types"
 )
@@ -41,17 +41,16 @@ const eventsSchema = `
     state_snapshot_nid INTEGER NOT NULL DEFAULT 0,
     depth INTEGER NOT NULL,
     event_id TEXT NOT NULL UNIQUE,
-    reference_sha256 BLOB NOT NULL,
 	auth_event_nids TEXT NOT NULL DEFAULT '[]',
 	is_rejected BOOLEAN NOT NULL DEFAULT FALSE
   );
 `
 
 const insertEventSQL = `
-	INSERT INTO roomserver_events (room_nid, event_type_nid, event_state_key_nid, event_id, reference_sha256, auth_event_nids, depth, is_rejected)
-	  VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
+	INSERT INTO roomserver_events (room_nid, event_type_nid, event_state_key_nid, event_id, auth_event_nids, depth, is_rejected)
+	  VALUES ($1, $2, $3, $4, $5, $6, $7)
 	  ON CONFLICT DO UPDATE
-	  SET is_rejected = $8 WHERE is_rejected = 1
+	  SET is_rejected = $7 WHERE is_rejected = 1
 	  RETURNING event_nid, state_snapshot_nid;
 `
 
@@ -100,12 +99,9 @@ const selectEventIDSQL = "" +
 	"SELECT event_id FROM roomserver_events WHERE event_nid = $1"
 
 const bulkSelectStateAtEventAndReferenceSQL = "" +
-	"SELECT event_type_nid, event_state_key_nid, event_nid, state_snapshot_nid, event_id, reference_sha256" +
+	"SELECT event_type_nid, event_state_key_nid, event_nid, state_snapshot_nid, event_id" +
 	" FROM roomserver_events WHERE event_nid IN ($1)"
 
-const bulkSelectEventReferenceSQL = "" +
-	"SELECT event_id, reference_sha256 FROM roomserver_events WHERE event_nid IN ($1)"
-
 const bulkSelectEventIDSQL = "" +
 	"SELECT event_nid, event_id FROM roomserver_events WHERE event_nid IN ($1)"
 
@@ -137,7 +133,6 @@ type eventStatements struct {
 	updateEventSentToOutputStmt                   *sql.Stmt
 	selectEventIDStmt                             *sql.Stmt
 	bulkSelectStateAtEventAndReferenceStmt        *sql.Stmt
-	bulkSelectEventReferenceStmt                  *sql.Stmt
 	bulkSelectEventIDStmt                         *sql.Stmt
 	selectEventRejectedStmt                       *sql.Stmt
 	//bulkSelectEventNIDStmt               *sql.Stmt
@@ -147,7 +142,32 @@ type eventStatements struct {
 
 func CreateEventsTable(db *sql.DB) error {
 	_, err := db.Exec(eventsSchema)
-	return err
+	if err != nil {
+		return err
+	}
+
+	// check if the column exists
+	var cName string
+	migrationName := "roomserver: drop column reference_sha from roomserver_events"
+	err = db.QueryRowContext(context.Background(), `SELECT p.name FROM sqlite_master AS m JOIN pragma_table_info(m.name) AS p WHERE m.name = 'roomserver_events' AND p.name = 'reference_sha256'`).Scan(&cName)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) { // migration was already executed, as the column was removed
+			if err = sqlutil.InsertMigration(context.Background(), db, migrationName); err != nil {
+				return fmt.Errorf("unable to manually insert migration '%s': %w", migrationName, err)
+			}
+			return nil
+		}
+		return err
+	}
+
+	m := sqlutil.NewMigrator(db)
+	m.AddMigrations([]sqlutil.Migration{
+		{
+			Version: migrationName,
+			Up:      deltas.UpDropEventReferenceSHA,
+		},
+	}...)
+	return m.Up(context.Background())
 }
 
 func PrepareEventsTable(db *sql.DB) (tables.Events, error) {
@@ -167,7 +187,6 @@ func PrepareEventsTable(db *sql.DB) (tables.Events, error) {
 		{&s.selectEventSentToOutputStmt, selectEventSentToOutputSQL},
 		{&s.selectEventIDStmt, selectEventIDSQL},
 		{&s.bulkSelectStateAtEventAndReferenceStmt, bulkSelectStateAtEventAndReferenceSQL},
-		{&s.bulkSelectEventReferenceStmt, bulkSelectEventReferenceSQL},
 		{&s.bulkSelectEventIDStmt, bulkSelectEventIDSQL},
 		//{&s.bulkSelectEventNIDStmt, bulkSelectEventNIDSQL},
 		//{&s.bulkSelectUnsentEventNIDStmt, bulkSelectUnsentEventNIDSQL},
@@ -183,7 +202,6 @@ func (s *eventStatements) InsertEvent(
 	eventTypeNID types.EventTypeNID,
 	eventStateKeyNID types.EventStateKeyNID,
 	eventID string,
-	referenceSHA256 []byte,
 	authEventNIDs []types.EventNID,
 	depth int64,
 	isRejected bool,
@@ -194,7 +212,7 @@ func (s *eventStatements) InsertEvent(
 	insertStmt := sqlutil.TxStmt(txn, s.insertEventStmt)
 	err := insertStmt.QueryRowContext(
 		ctx, int64(roomNID), int64(eventTypeNID), int64(eventStateKeyNID),
-		eventID, referenceSHA256, eventNIDsAsArray(authEventNIDs), depth, isRejected,
+		eventID, eventNIDsAsArray(authEventNIDs), depth, isRejected,
 	).Scan(&eventNID, &stateNID)
 	return types.EventNID(eventNID), types.StateSnapshotNID(stateNID), err
 }
@@ -475,11 +493,10 @@ func (s *eventStatements) BulkSelectStateAtEventAndReference(
 		eventNID         int64
 		stateSnapshotNID int64
 		eventID          string
-		eventSHA256      []byte
 	)
 	for ; rows.Next(); i++ {
 		if err = rows.Scan(
-			&eventTypeNID, &eventStateKeyNID, &eventNID, &stateSnapshotNID, &eventID, &eventSHA256,
+			&eventTypeNID, &eventStateKeyNID, &eventNID, &stateSnapshotNID, &eventID,
 		); err != nil {
 			return nil, err
 		}
@@ -489,43 +506,6 @@ func (s *eventStatements) BulkSelectStateAtEventAndReference(
 		result.EventNID = types.EventNID(eventNID)
 		result.BeforeStateSnapshotNID = types.StateSnapshotNID(stateSnapshotNID)
 		result.EventID = eventID
-		result.EventSHA256 = eventSHA256
-	}
-	if i != len(eventNIDs) {
-		return nil, fmt.Errorf("storage: event NIDs missing from the database (%d != %d)", i, len(eventNIDs))
-	}
-	return results, nil
-}
-
-func (s *eventStatements) BulkSelectEventReference(
-	ctx context.Context, txn *sql.Tx, eventNIDs []types.EventNID,
-) ([]gomatrixserverlib.EventReference, error) {
-	///////////////
-	iEventNIDs := make([]interface{}, len(eventNIDs))
-	for k, v := range eventNIDs {
-		iEventNIDs[k] = v
-	}
-	selectOrig := strings.Replace(bulkSelectEventReferenceSQL, "($1)", sqlutil.QueryVariadic(len(iEventNIDs)), 1)
-	selectPrep, err := s.db.Prepare(selectOrig)
-	if err != nil {
-		return nil, err
-	}
-	defer selectPrep.Close() // nolint:errcheck
-	///////////////
-
-	selectStmt := sqlutil.TxStmt(txn, selectPrep)
-	rows, err := selectStmt.QueryContext(ctx, iEventNIDs...)
-	if err != nil {
-		return nil, err
-	}
-	defer internal.CloseAndLogIfError(ctx, rows, "bulkSelectEventReference: rows.close() failed")
-	results := make([]gomatrixserverlib.EventReference, len(eventNIDs))
-	i := 0
-	for ; rows.Next(); i++ {
-		result := &results[i]
-		if err = rows.Scan(&result.EventID, &result.EventSHA256); err != nil {
-			return nil, err
-		}
 	}
 	if i != len(eventNIDs) {
 		return nil, fmt.Errorf("storage: event NIDs missing from the database (%d != %d)", i, len(eventNIDs))
diff --git a/roomserver/storage/sqlite3/previous_events_table.go b/roomserver/storage/sqlite3/previous_events_table.go
index 2a146ef6..4e59fbba 100644
--- a/roomserver/storage/sqlite3/previous_events_table.go
+++ b/roomserver/storage/sqlite3/previous_events_table.go
@@ -18,10 +18,12 @@ package sqlite3
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"strings"
 
 	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/roomserver/storage/sqlite3/deltas"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 	"github.com/matrix-org/dendrite/roomserver/types"
 )
@@ -34,9 +36,8 @@ import (
 const previousEventSchema = `
   CREATE TABLE IF NOT EXISTS roomserver_previous_events (
     previous_event_id TEXT NOT NULL,
-    previous_reference_sha256 BLOB,
     event_nids TEXT NOT NULL,
-    UNIQUE (previous_event_id, previous_reference_sha256)
+    UNIQUE (previous_event_id)
   );
 `
 
@@ -47,20 +48,20 @@ const previousEventSchema = `
 // The lock is necessary to avoid data races when checking whether an event is already referenced by another event.
 const insertPreviousEventSQL = `
 	INSERT OR REPLACE INTO roomserver_previous_events
-	  (previous_event_id, previous_reference_sha256, event_nids)
-	  VALUES ($1, $2, $3)
+	  (previous_event_id, event_nids)
+	  VALUES ($1, $2)
 `
 
 const selectPreviousEventNIDsSQL = `
 	SELECT event_nids FROM roomserver_previous_events
-	  WHERE previous_event_id = $1 AND previous_reference_sha256 = $2
+	  WHERE previous_event_id = $1
 `
 
 // Check if the event is referenced by another event in the table.
 // This should only be done while holding a "FOR UPDATE" lock on the row in the rooms table for this room.
 const selectPreviousEventExistsSQL = `
 	SELECT 1 FROM roomserver_previous_events
-	  WHERE previous_event_id = $1 AND previous_reference_sha256 = $2
+	  WHERE previous_event_id = $1
 `
 
 type previousEventStatements struct {
@@ -72,7 +73,30 @@ type previousEventStatements struct {
 
 func CreatePrevEventsTable(db *sql.DB) error {
 	_, err := db.Exec(previousEventSchema)
-	return err
+	if err != nil {
+		return err
+	}
+	// check if the column exists
+	var cName string
+	migrationName := "roomserver: drop column reference_sha from roomserver_prev_events"
+	err = db.QueryRowContext(context.Background(), `SELECT p.name FROM sqlite_master AS m JOIN pragma_table_info(m.name) AS p WHERE m.name = 'roomserver_previous_events' AND p.name = 'previous_reference_sha256'`).Scan(&cName)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) { // migration was already executed, as the column was removed
+			if err = sqlutil.InsertMigration(context.Background(), db, migrationName); err != nil {
+				return fmt.Errorf("unable to manually insert migration '%s': %w", migrationName, err)
+			}
+			return nil
+		}
+		return err
+	}
+	m := sqlutil.NewMigrator(db)
+	m.AddMigrations([]sqlutil.Migration{
+		{
+			Version: migrationName,
+			Up:      deltas.UpDropEventReferenceSHAPrevEvents,
+		},
+	}...)
+	return m.Up(context.Background())
 }
 
 func PreparePrevEventsTable(db *sql.DB) (tables.PreviousEvents, error) {
@@ -91,13 +115,12 @@ func (s *previousEventStatements) InsertPreviousEvent(
 	ctx context.Context,
 	txn *sql.Tx,
 	previousEventID string,
-	previousEventReferenceSHA256 []byte,
 	eventNID types.EventNID,
 ) error {
 	var eventNIDs string
 	eventNIDAsString := fmt.Sprintf("%d", eventNID)
 	selectStmt := sqlutil.TxStmt(txn, s.selectPreviousEventExistsStmt)
-	err := selectStmt.QueryRowContext(ctx, previousEventID, previousEventReferenceSHA256).Scan(&eventNIDs)
+	err := selectStmt.QueryRowContext(ctx, previousEventID).Scan(&eventNIDs)
 	if err != nil && err != sql.ErrNoRows {
 		return fmt.Errorf("selectStmt.QueryRowContext.Scan: %w", err)
 	}
@@ -115,7 +138,7 @@ func (s *previousEventStatements) InsertPreviousEvent(
 	}
 	insertStmt := sqlutil.TxStmt(txn, s.insertPreviousEventStmt)
 	_, err = insertStmt.ExecContext(
-		ctx, previousEventID, previousEventReferenceSHA256, eventNIDs,
+		ctx, previousEventID, eventNIDs,
 	)
 	return err
 }
@@ -123,9 +146,9 @@ func (s *previousEventStatements) InsertPreviousEvent(
 // Check if the event reference exists
 // Returns sql.ErrNoRows if the event reference doesn't exist.
 func (s *previousEventStatements) SelectPreviousEventExists(
-	ctx context.Context, txn *sql.Tx, eventID string, eventReferenceSHA256 []byte,
+	ctx context.Context, txn *sql.Tx, eventID string,
 ) error {
 	var ok int64
 	stmt := sqlutil.TxStmt(txn, s.selectPreviousEventExistsStmt)
-	return stmt.QueryRowContext(ctx, eventID, eventReferenceSHA256).Scan(&ok)
+	return stmt.QueryRowContext(ctx, eventID).Scan(&ok)
 }
diff --git a/roomserver/storage/sqlite3/storage.go b/roomserver/storage/sqlite3/storage.go
index 89e16fc1..6ab427a8 100644
--- a/roomserver/storage/sqlite3/storage.go
+++ b/roomserver/storage/sqlite3/storage.go
@@ -21,14 +21,13 @@ import (
 	"errors"
 	"fmt"
 
-	"github.com/matrix-org/gomatrixserverlib"
-
 	"github.com/matrix-org/dendrite/internal/caching"
 	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/roomserver/storage/shared"
 	"github.com/matrix-org/dendrite/roomserver/storage/sqlite3/deltas"
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/gomatrixserverlib"
 )
 
 // A Database is used to store room events and stream offsets.
diff --git a/roomserver/storage/tables/events_table_test.go b/roomserver/storage/tables/events_table_test.go
index 107af478..5ed80564 100644
--- a/roomserver/storage/tables/events_table_test.go
+++ b/roomserver/storage/tables/events_table_test.go
@@ -11,7 +11,6 @@ import (
 	"github.com/matrix-org/dendrite/roomserver/types"
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dendrite/test"
-	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -48,10 +47,9 @@ func Test_EventsTable(t *testing.T) {
 		// create some dummy data
 		eventIDs := make([]string, 0, len(room.Events()))
 		wantStateAtEvent := make([]types.StateAtEvent, 0, len(room.Events()))
-		wantEventReferences := make([]gomatrixserverlib.EventReference, 0, len(room.Events()))
 		wantStateAtEventAndRefs := make([]types.StateAtEventAndReference, 0, len(room.Events()))
 		for _, ev := range room.Events() {
-			eventNID, snapNID, err := tab.InsertEvent(ctx, nil, 1, 1, 1, ev.EventID(), ev.EventReference().EventSHA256, nil, ev.Depth(), false)
+			eventNID, snapNID, err := tab.InsertEvent(ctx, nil, 1, 1, 1, ev.EventID(), nil, ev.Depth(), false)
 			assert.NoError(t, err)
 			gotEventNID, gotSnapNID, err := tab.SelectEvent(ctx, nil, ev.EventID())
 			assert.NoError(t, err)
@@ -75,7 +73,6 @@ func Test_EventsTable(t *testing.T) {
 			assert.True(t, sentToOutput)
 
 			eventIDs = append(eventIDs, ev.EventID())
-			wantEventReferences = append(wantEventReferences, ev.EventReference())
 
 			// Set the stateSnapshot to 2 for some events to verify they are returned later
 			stateSnapshot := 0
@@ -97,8 +94,8 @@ func Test_EventsTable(t *testing.T) {
 			}
 			wantStateAtEvent = append(wantStateAtEvent, stateAtEvent)
 			wantStateAtEventAndRefs = append(wantStateAtEventAndRefs, types.StateAtEventAndReference{
-				StateAtEvent:   stateAtEvent,
-				EventReference: ev.EventReference(),
+				StateAtEvent: stateAtEvent,
+				EventID:      ev.EventID(),
 			})
 		}
 
@@ -140,10 +137,6 @@ func Test_EventsTable(t *testing.T) {
 			assert.True(t, ok)
 		}
 
-		references, err := tab.BulkSelectEventReference(ctx, nil, nids)
-		assert.NoError(t, err)
-		assert.Equal(t, wantEventReferences, references)
-
 		stateAndRefs, err := tab.BulkSelectStateAtEventAndReference(ctx, nil, nids)
 		assert.NoError(t, err)
 		assert.Equal(t, wantStateAtEventAndRefs, stateAndRefs)
diff --git a/roomserver/storage/tables/interface.go b/roomserver/storage/tables/interface.go
index a9c5f8b1..333483b3 100644
--- a/roomserver/storage/tables/interface.go
+++ b/roomserver/storage/tables/interface.go
@@ -42,7 +42,7 @@ type Events interface {
 	InsertEvent(
 		ctx context.Context, txn *sql.Tx, roomNID types.RoomNID, eventTypeNID types.EventTypeNID,
 		eventStateKeyNID types.EventStateKeyNID, eventID string,
-		referenceSHA256 []byte, authEventNIDs []types.EventNID, depth int64, isRejected bool,
+		authEventNIDs []types.EventNID, depth int64, isRejected bool,
 	) (types.EventNID, types.StateSnapshotNID, error)
 	SelectEvent(ctx context.Context, txn *sql.Tx, eventID string) (types.EventNID, types.StateSnapshotNID, error)
 	BulkSelectSnapshotsFromEventIDs(ctx context.Context, txn *sql.Tx, eventIDs []string) (map[types.StateSnapshotNID][]string, error)
@@ -59,7 +59,6 @@ type Events interface {
 	UpdateEventSentToOutput(ctx context.Context, txn *sql.Tx, eventNID types.EventNID) error
 	SelectEventID(ctx context.Context, txn *sql.Tx, eventNID types.EventNID) (eventID string, err error)
 	BulkSelectStateAtEventAndReference(ctx context.Context, txn *sql.Tx, eventNIDs []types.EventNID) ([]types.StateAtEventAndReference, error)
-	BulkSelectEventReference(ctx context.Context, txn *sql.Tx, eventNIDs []types.EventNID) ([]gomatrixserverlib.EventReference, error)
 	// BulkSelectEventID returns a map from numeric event ID to string event ID.
 	BulkSelectEventID(ctx context.Context, txn *sql.Tx, eventNIDs []types.EventNID) (map[types.EventNID]string, error)
 	// BulkSelectEventNIDs returns a map from string event ID to numeric event ID.
@@ -113,10 +112,10 @@ type RoomAliases interface {
 }
 
 type PreviousEvents interface {
-	InsertPreviousEvent(ctx context.Context, txn *sql.Tx, previousEventID string, previousEventReferenceSHA256 []byte, eventNID types.EventNID) error
+	InsertPreviousEvent(ctx context.Context, txn *sql.Tx, previousEventID string, eventNID types.EventNID) error
 	// Check if the event reference exists
 	// Returns sql.ErrNoRows if the event reference doesn't exist.
-	SelectPreviousEventExists(ctx context.Context, txn *sql.Tx, eventID string, eventReferenceSHA256 []byte) error
+	SelectPreviousEventExists(ctx context.Context, txn *sql.Tx, eventID string) error
 }
 
 type Invites interface {
diff --git a/roomserver/storage/tables/previous_events_table_test.go b/roomserver/storage/tables/previous_events_table_test.go
index 63d54069..9d41e90b 100644
--- a/roomserver/storage/tables/previous_events_table_test.go
+++ b/roomserver/storage/tables/previous_events_table_test.go
@@ -45,17 +45,17 @@ func TestPreviousEventsTable(t *testing.T) {
 		defer close()
 
 		for _, x := range room.Events() {
-			for _, prevEvent := range x.PrevEvents() {
-				err := tab.InsertPreviousEvent(ctx, nil, prevEvent.EventID, prevEvent.EventSHA256, 1)
+			for _, eventID := range x.PrevEventIDs() {
+				err := tab.InsertPreviousEvent(ctx, nil, eventID, 1)
 				assert.NoError(t, err)
 
-				err = tab.SelectPreviousEventExists(ctx, nil, prevEvent.EventID, prevEvent.EventSHA256)
+				err = tab.SelectPreviousEventExists(ctx, nil, eventID)
 				assert.NoError(t, err)
 			}
 		}
 
-		// RandomString with a correct EventSHA256 should fail and return sql.ErrNoRows
-		err := tab.SelectPreviousEventExists(ctx, nil, util.RandomString(16), room.Events()[0].EventReference().EventSHA256)
+		// RandomString should fail and return sql.ErrNoRows
+		err := tab.SelectPreviousEventExists(ctx, nil, util.RandomString(16))
 		assert.Error(t, err)
 	})
 }
diff --git a/roomserver/types/types.go b/roomserver/types/types.go
index e986b9da..f57978ad 100644
--- a/roomserver/types/types.go
+++ b/roomserver/types/types.go
@@ -200,7 +200,7 @@ func (s StateAtEvent) IsStateEvent() bool {
 // The StateAtEvent is used to construct the current state of the room from the latest events.
 type StateAtEventAndReference struct {
 	StateAtEvent
-	gomatrixserverlib.EventReference
+	EventID string
 }
 
 type StateAtEventAndReferences []StateAtEventAndReference
diff --git a/test/room.go b/test/room.go
index 1c0f01e4..852e3153 100644
--- a/test/room.go
+++ b/test/room.go
@@ -75,7 +75,7 @@ func NewRoom(t *testing.T, creator *User, modifiers ...roomModifier) *Room {
 	return r
 }
 
-func (r *Room) MustGetAuthEventRefsForEvent(t *testing.T, needed gomatrixserverlib.StateNeeded) []gomatrixserverlib.EventReference {
+func (r *Room) MustGetAuthEventRefsForEvent(t *testing.T, needed gomatrixserverlib.StateNeeded) []string {
 	t.Helper()
 	a, err := needed.AuthEventReferences(&r.authEvents)
 	if err != nil {
@@ -176,7 +176,7 @@ func (r *Room) CreateEvent(t *testing.T, creator *User, eventType string, conten
 		t.Fatalf("CreateEvent[%s]: failed to SetContent: %s", eventType, err)
 	}
 	if depth > 1 {
-		builder.PrevEvents = []gomatrixserverlib.EventReference{r.events[len(r.events)-1].EventReference()}
+		builder.PrevEvents = []string{r.events[len(r.events)-1].EventID()}
 	}
 
 	err = builder.AddAuthEvents(&r.authEvents)