Nullifier cache only hits db if needed

yarn-project/sequencer-client/src/tx_validator/nullifier_cache.test.ts

@@ -0,0 +1,57 @@
+import { MerkleTreeId, type MerkleTreeReadOperations } from '@aztec/circuit-types';
+import { times } from '@aztec/foundation/collection';
+
+import { type MockProxy, mock } from 'jest-mock-extended';
+
+import { NullifierCache } from './nullifier_cache.js';
+
+describe('NullifierCache', () => {
+  let nullifierCache: NullifierCache;
+  let db: MockProxy<MerkleTreeReadOperations>;
+  let nullifiers: Buffer[];
+
+  beforeEach(() => {
+    db = mock<MerkleTreeReadOperations>();
+    nullifierCache = new NullifierCache(db);
+    nullifiers = [Buffer.alloc(1, 1), Buffer.alloc(1, 2), Buffer.alloc(1, 3)];
+  });
+
+  it('checks nullifier existence against cache', async () => {
+    nullifierCache.addNullifiers([nullifiers[0], nullifiers[1]]);
+    db.findLeafIndices.mockResolvedValue([]);
+    await expect(nullifierCache.nullifiersExist(nullifiers)).resolves.toEqual([true, true, false]);
+  });
+
+  it('checks nullifier existence against db', async () => {
+    db.findLeafIndices.mockResolvedValue([1n, 2n, undefined]);
+    await expect(nullifierCache.nullifiersExist(nullifiers)).resolves.toEqual([true, true, false]);
+  });
+
+  it('checks nullifier existence against db only on cache miss', async () => {
+    nullifierCache.addNullifiers([nullifiers[0]]);
+    db.findLeafIndices.mockResolvedValue([2n, undefined]);
+    const result = await nullifierCache.nullifiersExist(nullifiers);
+    expect(db.findLeafIndices).toHaveBeenCalledWith(MerkleTreeId.NULLIFIER_TREE, [nullifiers[1], nullifiers[2]]);
+    expect(result).toEqual([true, true, false]);
+  });
+
+  it('checks existence with several nullifiers', async () => {
+    // Split 60 nullifiers evenly across db, cache, or not found
+    const nullifiers = times(60, i => Buffer.alloc(1, i));
+    const where = nullifiers.map((_, i) =>
+      i % 3 === 0 ? ('db' as const) : i % 3 === 1 ? ('cache' as const) : ('none' as const),
+    );
+
+    // Add to the cache nullifiers flagged as cache
+    nullifierCache.addNullifiers(nullifiers.filter((_, i) => where[i] === 'cache'));
+    // The db should be queried only with nullifiers not in the cache, return true for half of them then
+    db.findLeafIndices.mockResolvedValue(times(40, i => (i % 2 === 0 ? BigInt(i) : undefined)));
+
+    const result = await nullifierCache.nullifiersExist(nullifiers);
+    expect(db.findLeafIndices).toHaveBeenCalledWith(
+      MerkleTreeId.NULLIFIER_TREE,
+      nullifiers.filter((_, i) => where[i] !== 'cache'),
+    );
+    expect(result).toEqual(times(60, i => where[i] !== 'none'));
+  });
+});

yarn-project/sequencer-client/src/tx_validator/nullifier_cache.ts

@@ -12,12 +12,16 @@ export class NullifierCache implements NullifierSource {
     this.nullifiers = new Set();
   }
 
-  async nullifiersExist(nullifiers: Buffer[]): Promise<boolean[]> {
-    const dbIndices = await this.db.findLeafIndices(MerkleTreeId.NULLIFIER_TREE, nullifiers);
-    return nullifiers.map((n, index) => this.nullifiers.has(n.toString()) || dbIndices[index] !== undefined);
+  public async nullifiersExist(nullifiers: Buffer[]): Promise<boolean[]> {
+    const cacheResults = nullifiers.map(n => this.nullifiers.has(n.toString()));
+    const toCheckDb = nullifiers.filter((_n, index) => !cacheResults[index]);
+    const dbHits = await this.db.findLeafIndices(MerkleTreeId.NULLIFIER_TREE, toCheckDb);
+
+    let dbIndex = 0;
+    return nullifiers.map((_n, index) => cacheResults[index] || dbHits[dbIndex++] !== undefined);
   }
 
-  addNullifiers(nullifiers: Buffer[]) {
+  public addNullifiers(nullifiers: Buffer[]) {
     for (const nullifier of nullifiers) {
       this.nullifiers.add(nullifier.toString());
     }