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// Copyright 2018 New Vector Ltd
//
// 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/common"
)
// The purpose of this table is to keep track of backwards extremities for a room.
// Backwards extremities are the earliest (DAG-wise) known events which we have
// the entire event JSON. These event IDs are used in federation requests to fetch
// even earlier events.
//
// We persist the previous event IDs as well, one per row, so when we do fetch even
// earlier events we can simply delete rows which referenced it. Consider the graph:
// A
// | Event C has 1 prev_event ID: A.
// B C
// |___| Event D has 2 prev_event IDs: B and C.
// |
// D
// The earliest known event we have is D, so this table has 2 rows.
// A backfill request gives us C but not B. We delete rows where prev_event=C. This
// still means that D is a backwards extremity as we do not have event B. However, event
// C is *also* a backwards extremity at this point as we do not have event A. Later,
// when we fetch event B, we delete rows where prev_event=B. This then removes D as
// a backwards extremity because there are no more rows with event_id=B.
const backwardExtremitiesSchema = `
-- Stores output room events received from the roomserver.
CREATE TABLE IF NOT EXISTS syncapi_backward_extremities (
-- The 'room_id' key for the event.
room_id TEXT NOT NULL,
-- The event ID for the last known event. This is the backwards extremity.
event_id TEXT NOT NULL,
-- The prev_events for the last known event. This is used to update extremities.
prev_event_id TEXT NOT NULL,
PRIMARY KEY(room_id, event_id, prev_event_id)
);
`
const insertBackwardExtremitySQL = "" +
"INSERT INTO syncapi_backward_extremities (room_id, event_id, prev_event_id)" +
" VALUES ($1, $2, $3)" +
" ON CONFLICT DO NOTHING"
const selectBackwardExtremitiesForRoomSQL = "" +
"SELECT event_id FROM syncapi_backward_extremities WHERE room_id = $1"
const deleteBackwardExtremitySQL = "" +
"DELETE FROM syncapi_backward_extremities WHERE room_id = $1 AND prev_event_id = $2"
type backwardExtremitiesStatements struct {
insertBackwardExtremityStmt *sql.Stmt
selectBackwardExtremitiesForRoomStmt *sql.Stmt
deleteBackwardExtremityStmt *sql.Stmt
}
func (s *backwardExtremitiesStatements) prepare(db *sql.DB) (err error) {
_, err = db.Exec(backwardExtremitiesSchema)
if err != nil {
return
}
if s.insertBackwardExtremityStmt, err = db.Prepare(insertBackwardExtremitySQL); err != nil {
return
}
if s.selectBackwardExtremitiesForRoomStmt, err = db.Prepare(selectBackwardExtremitiesForRoomSQL); err != nil {
return
}
if s.deleteBackwardExtremityStmt, err = db.Prepare(deleteBackwardExtremitySQL); err != nil {
return
}
return
}
func (s *backwardExtremitiesStatements) insertsBackwardExtremity(
ctx context.Context, txn *sql.Tx, roomID, eventID string, prevEventID string,
) (err error) {
_, err = txn.Stmt(s.insertBackwardExtremityStmt).ExecContext(ctx, roomID, eventID, prevEventID)
return
}
func (s *backwardExtremitiesStatements) selectBackwardExtremitiesForRoom(
ctx context.Context, roomID string,
) (eventIDs []string, err error) {
rows, err := s.selectBackwardExtremitiesForRoomStmt.QueryContext(ctx, roomID)
if err != nil {
return
}
defer common.CloseAndLogIfError(ctx, rows, "selectBackwardExtremitiesForRoom: rows.close() failed")
for rows.Next() {
var eID string
if err = rows.Scan(&eID); err != nil {
return
}
eventIDs = append(eventIDs, eID)
}
return eventIDs, rows.Err()
}
func (s *backwardExtremitiesStatements) deleteBackwardExtremity(
ctx context.Context, txn *sql.Tx, roomID, knownEventID string,
) (err error) {
_, err = txn.Stmt(s.deleteBackwardExtremityStmt).ExecContext(ctx, roomID, knownEventID)
return
}
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