From f2c67b902e55b475b74f8ea159e8d4fdd1089f88 Mon Sep 17 00:00:00 2001
From: Juha Paananen <juha.paananen@gmail.com>
Date: Sun, 28 Jan 2024 21:38:05 +0200
Subject: [PATCH] Save board snapshot every 5000 events to avoid excessively
 long board load time due to snapshot being late

---
 backend/src/board-state.ts | 30 ++++++++++++++++++++++++++----
 backend/src/board-store.ts |  9 +++++----
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/backend/src/board-state.ts b/backend/src/board-state.ts
index 0b2c39b84..7a10d6a48 100644
--- a/backend/src/board-state.ts
+++ b/backend/src/board-state.ts
@@ -1,14 +1,23 @@
 import { boardReducer } from "../../common/src/board-reducer"
 import { Board, BoardCursorPositions, BoardHistoryEntry, Id, ItemLocks, Serial } from "../../common/src/domain"
 import { Locks } from "./locker"
-import { createAccessToken, createBoard, fetchBoard, saveRecentEvents } from "./board-store"
+import {
+    createAccessToken,
+    createBoard,
+    fetchBoard,
+    mkSnapshot,
+    saveBoardSnapshot,
+    saveRecentEvents,
+} from "./board-store"
 import { broadcastItemLocks, getBoardSessionCount, getSessionCount } from "./websocket-sessions"
 import { compactBoardHistory, quickCompactBoardHistory } from "./compact-history"
 import { sleep } from "../../common/src/sleep"
 import { UserSession } from "./websocket-sessions"
+import { inTransaction } from "./db"
 // A mutable state object for server side state
 export type ServerSideBoardState = {
     ready: true
+    snapshotSerial: Serial
     board: Board
     recentEvents: BoardHistoryEntry[]
     storingEvents: BoardHistoryEntry[]
@@ -35,7 +44,7 @@ export async function getBoard(id: Id): Promise<ServerSideBoardState | null> {
         const fetchState = async () => {
             const boardData = await fetchBoard(id)
             if (!boardData) return null
-            const { board, accessTokens } = boardData
+            const { board, accessTokens, snapshotSerial } = boardData
             return {
                 ready: true,
                 board,
@@ -46,6 +55,7 @@ export async function getBoard(id: Id): Promise<ServerSideBoardState | null> {
                 cursorsMoved: false,
                 cursorPositions: {},
                 sessions: [],
+                snapshotSerial,
             } as ServerSideBoardState
         }
         const fetch = fetchState()
@@ -100,10 +110,10 @@ export function updateBoards(boardState: ServerSideBoardState, appEvent: BoardHi
 export async function addBoard(board: Board, createToken?: boolean): Promise<ServerSideBoardState> {
     await createBoard(board)
     const accessTokens = createToken ? [await createAccessToken(board)] : []
-    const boardState = {
+    const boardState: ServerSideBoardState = {
         ready: true as const,
         board,
-        serial: 0,
+        snapshotSerial: 0,
         recentEvents: [],
         storingEvents: [],
         locks: Locks((changedLocks) => broadcastItemLocks(board.id, changedLocks)),
@@ -145,6 +155,18 @@ async function saveBoardChanges(state: ServerSideBoardState) {
         )
         try {
             await saveRecentEvents(state.board.id, state.storingEvents)
+            if (state.board.serial - state.snapshotSerial > 5000) {
+                console.log(
+                    `Saving snapshot for board ${state.board.id} with ${
+                        state.board.serial - state.snapshotSerial
+                    } new events`,
+                )
+                await inTransaction(async (client) => {
+                    await saveBoardSnapshot(mkSnapshot(state.board, state.board.serial), client)
+                })
+                state.snapshotSerial = state.board.serial
+            }
+            // TODO: also update snapshot if more than 1000 events since snapshot
         } catch (e) {
             // Push event back to the head of save list for retrying later
             state.recentEvents = [...state.storingEvents, ...state.recentEvents]
diff --git a/backend/src/board-store.ts b/backend/src/board-store.ts
index b460dafe8..b4accc3e9 100644
--- a/backend/src/board-store.ts
+++ b/backend/src/board-store.ts
@@ -6,9 +6,10 @@ import { Board, BoardAccessPolicy, BoardHistoryEntry, Id, isBoardEmpty, Serial }
 import { migrateBoard, migrateEvent, mkBootStrapEvent } from "../../common/src/migration"
 import { inTransaction, withDBClient } from "./db"
 
-export type BoardAndAccessTokens = {
+export type BoardFetchResult = {
     board: Board
     accessTokens: string[]
+    snapshotSerial: Serial
 }
 
 export type BoardInfo = {
@@ -37,7 +38,7 @@ select id,
 where id=$1
 `
 
-export async function fetchBoard(id: Id): Promise<BoardAndAccessTokens | null> {
+export async function fetchBoard(id: Id): Promise<BoardFetchResult | null> {
     return await inTransaction(async (client) => {
         const started = new Date().getTime()
         const result = await client.query(selectBoardQuery, [id])
@@ -100,7 +101,7 @@ export async function fetchBoard(id: Id): Promise<BoardAndAccessTokens | null> {
                 await client.query("SELECT token FROM board_api_token WHERE board_id=$1", [id])
             ).rows.map((row) => row.token)
 
-            return { board: { ...board, serial }, accessTokens }
+            return { board: { ...board, serial }, accessTokens, snapshotSerial: snapshot.serial }
         }
     })
 }
@@ -180,7 +181,7 @@ export async function createAccessToken(board: Board): Promise<string> {
 }
 
 export async function saveRecentEvents(id: Id, recentEvents: BoardHistoryEntry[]) {
-    await inTransaction(async (client) => storeEventHistoryBundle(id, recentEvents, client))
+    await inTransaction(async (client) => await storeEventHistoryBundle(id, recentEvents, client))
 }
 
 type StreamingBoardEventCallback = (chunk: BoardHistoryEntry[]) => void