WIP re-implement persistence with compaction

src/persistence.ts

@@ -0,0 +1,149 @@
+import * as Y from 'yjs';
+import { docsDb, LOCAL_DELTA_STORE } from './sync';
+import { assert } from './util';
+import _ from 'lodash';
+
+const COMPACTION_THRESHOLD = 200;
+
+export async function openDoc(id: string): Promise<Y.Doc> {
+  // Return existing doc if we still have it open
+  const previousState = idToState.get(id);
+  if (previousState) {
+    previousState.refCount += 1;
+    return previousState.ydoc;
+  }
+
+  const state = await initialLoad(id);
+  idToState.set(id, state);
+  docToState.set(state.ydoc, state);
+
+  return state.ydoc;
+}
+
+export function closeDoc(doc: Y.Doc) {
+  const state = docToState.get(doc);
+  assert(state, 'Document is not already open');
+
+  state.refCount -= 1;
+  if (state.refCount <= 0) {
+    idToState.delete(state.id);
+    docToState.delete(doc);
+    doc.destroy();
+  }
+}
+
+const idToState = new Map<string, State>();
+const docToState = new Map<Y.Doc, State>();
+
+type State = {
+  // TODO: Move more of this into class
+  id: string;
+  deltaBuffer: Uint8Array[];
+  numRecords: number;
+  refCount: number;
+  ydoc: Y.Doc;
+};
+
+async function initialLoad(id: string): Promise<State> {
+  const ydoc = new Y.Doc();
+  const records = await docsDb.getAll(
+    LOCAL_DELTA_STORE,
+    IDBKeyRange.bound([id, -Infinity], [id, Infinity])
+  );
+  Y.applyUpdate(ydoc, Y.mergeUpdates(records));
+  return {
+    id,
+    deltaBuffer: [],
+    numRecords: records.length,
+    refCount: 1,
+    ydoc,
+  };
+}
+
+class BufferedWriter {
+  private deltaBuffer: Uint8Array[];
+  private docId: string;
+  private numRecords: number;
+  private debouncedFlush: () => void;
+  private ydoc: Y.Doc;
+
+  constructor(docId: string) {
+    this.deltaBuffer = [];
+    this.docId = docId;
+    this.numRecords = 0;
+    this.debouncedFlush = _.debounce(
+      () => {
+        this.flush();
+      },
+      1_000,
+      { maxWait: 30_000 }
+    );
+    this.ydoc = new Y.Doc();
+  }
+
+  public async connect(): Promise<Y.Doc> {
+    const records = await docsDb.getAll(
+      LOCAL_DELTA_STORE,
+      IDBKeyRange.bound([this.docId, -Infinity], [this.docId, Infinity])
+    );
+    this.numRecords = records.length;
+    Y.applyUpdate(this.ydoc, Y.mergeUpdates(records));
+    this.ydoc.on('update', (blob) => this.addUpdate(blob));
+    return this.ydoc;
+  }
+
+  public addUpdate(update: Uint8Array) {
+    this.deltaBuffer.push(update);
+    this.debouncedFlush();
+  }
+
+  public async flush(): Promise<void> {
+    if (this.deltaBuffer.length === 0) {
+      return;
+    }
+
+    // Write delta
+    const delta = Y.mergeUpdates(this.deltaBuffer.splice(0));
+    try {
+      await docsDb.put(LOCAL_DELTA_STORE, delta, [
+        this.docId,
+        new Date().valueOf(),
+      ]);
+      this.numRecords += 1;
+    } catch (err) {
+      this.addUpdate(delta);
+      console.log(`Error flushing document ${this.docId}: ${err}`);
+      throw err;
+    }
+
+    // Compact if necessary
+    try {
+      await this.compact();
+    } catch (err) {
+      console.log(`Error compacting document ${this.docId}: ${err}`);
+    }
+  }
+
+  public async compact() {
+    if (this.numRecords < COMPACTION_THRESHOLD) {
+      return;
+    }
+    const tx = docsDb.transaction(LOCAL_DELTA_STORE, 'readwrite');
+
+    // Make sure we're not missing anything by pulling in all changes.
+    // This could happen if a document is being edited in two different tabs.
+    const fullRange = IDBKeyRange.bound(
+      [this.docId, -Infinity],
+      [this.docId, Infinity]
+    );
+    const records = await tx.store.getAll(fullRange);
+    Y.applyUpdate(this.ydoc, Y.mergeUpdates(records));
+
+    // Replace with a compacted blob
+    const compacted = Y.encodeStateAsUpdate(this.ydoc);
+    await tx.store.delete(fullRange);
+    await tx.store.put(compacted, [this.docId, new Date().valueOf()]);
+    tx.commit();
+    this.numRecords = 1;
+  }
+}

src/sync.ts

@@ -5,8 +5,8 @@ import { assert, generateId } from './util';
 import { getDocsMap, getVaultMap, type DocMap } from './vault';
 
 const DB_NAME = 'synced-docs';
-const LOCAL_DELTA_STORE = 'local-updates';
+export const LOCAL_DELTA_STORE = 'local-updates';
-const VAULT_STORE = 'vaults';
+export const VAULT_STORE = 'vaults';
 
 type LocalDeltaKey = [string, number];
 type VaultRecord = { id: string };
@@ -22,7 +22,7 @@ interface DocsDatabase extends DBSchema {
   };
 }
 
-const db = await openDB<DocsDatabase>(DB_NAME, 3, {
+export const docsDb = await openDB<DocsDatabase>(DB_NAME, 3, {
   upgrade(db, oldVersion, newVersion) {
     console.log(`Running upgrade from ${oldVersion} to ${newVersion}`);
     if (oldVersion < 2) {
@@ -59,7 +59,7 @@ export class LocalDocument {
 
   public static async load(id: string): Promise<LocalDocument> {
     // Build Y.Doc from records on disk
-    const updates: Uint8Array[] = await db.getAll(
+    const updates: Uint8Array[] = await docsDb.getAll(
       LOCAL_DELTA_STORE,
       IDBKeyRange.bound([id, -Infinity], [id, Infinity])
     );
@@ -78,7 +78,7 @@ export class LocalDocument {
     if (batch.length > 0) {
       const update = Y.mergeUpdates(batch);
       const key: LocalDeltaKey = [this.id, new Date().valueOf()];
-      await db.add(LOCAL_DELTA_STORE, update, key);
+      await docsDb.add(LOCAL_DELTA_STORE, update, key);
       this.totalUpdates += 1;
     }
   }
@@ -90,13 +90,13 @@ export class LocalDocument {
 }
 
 async function getOrCreateVaultDoc() {
-  const records = await db.getAll(VAULT_STORE);
+  const records = await docsDb.getAll(VAULT_STORE);
   if (records.length > 1) {
     throw new Error(`Expected 1 vault record, got ${records.length}`);
   } else if (records.length === 0) {
     const key = generateId();
     const value = { id: key };
-    await db.add(VAULT_STORE, value, key);
+    await docsDb.add(VAULT_STORE, value, key);
     records.push(value);
   }
 
@@ -135,7 +135,7 @@ if (docsMap.size === 0) {
     const docInfo = new Y.Map([['title', oldKey]]) as DocMap;
     docsMap.set(newId, docInfo);
 
-    const tx = db.transaction(LOCAL_DELTA_STORE, 'readwrite');
+    const tx = docsDb.transaction(LOCAL_DELTA_STORE, 'readwrite');
     const recordKeys = (await tx.store.getAllKeys(
       IDBKeyRange.bound([oldKey, -Infinity], [oldKey, Infinity])
     )) as LocalDeltaKey[];