Added config for caching the member lookup for link clicks (#21855)

https://linear.app/ghost/issue/ENG-1850/
- added cache/memoized the member uuid lookup within the
LinkClickRepository (used by the LinkClickTrackingService)
- added repository tests for the save method which were absent

This one one of a series of options we're testing out in order to smooth
out the surge in requests following a newsletter send. Most of this
activity is due to link checkers, but Ghost still needs to spend time
processing the member lookup to know whether or not it is a valid id,
and memoizing this lookup could significantly improve throughput by
reducing DB contention.

ghost/core/core/server/services/link-tracking/LinkClickRepository.js

@@ -2,6 +2,7 @@ const {LinkClick} = require('@tryghost/link-tracking');
 const ObjectID = require('bson-objectid').default;
 const sentry = require('../../../shared/sentry');
 const config = require('../../../shared/config');
+const _ = require('lodash');
 
 module.exports = class LinkClickRepository {
     /** @type {Object} */
@@ -28,6 +29,11 @@ module.exports = class LinkClickRepository {
         this.#Member = deps.Member;
         this.#MemberLinkClickEvent = deps.MemberLinkClickEvent;
         this.#DomainEvents = deps.DomainEvents;
+
+        // Memoize the findOne function
+        this.memoizedFindOne = _.memoize(async (uuid) => {
+            return await this.#Member.findOne({uuid});
+        });
     }
 
     async getAll(options) {
@@ -51,8 +57,14 @@ module.exports = class LinkClickRepository {
      * @returns {Promise<void>}
      */
     async save(linkClick) {
-        // Convert uuid to id
-        const member = await this.#Member.findOne({uuid: linkClick.member_uuid});
+        let member;
+
+        if (config && config.get('linkClickTrackingCacheMemberUuid')) {
+            member = await this.memoizedFindOne(linkClick.member_uuid);
+        } else {
+            member = await this.#Member.findOne({uuid: linkClick.member_uuid});
+        }
+
         if (!member) {
             if (config.get('bulkEmail:captureLinkClickBadMemberUuid')) {
                 sentry.captureMessage('LinkClickTrackingService > Member not found', {extra: {member_uuid: linkClick.member_uuid}});

ghost/core/core/shared/config/defaults.json

@@ -193,6 +193,7 @@
     "enableStripePromoCodes": false,
     "emailAnalytics": true,
     "linkClickTracking": true,
+    "linkClickTrackingCacheMemberUuid": false,
     "backgroundJobs": {
         "emailAnalytics": true,
         "clickTrackingLastSeenAtUpdater": true

ghost/core/test/unit/server/services/link-tracking/LinkClickRepository.test.js

@@ -0,0 +1,103 @@
+const should = require('should');
+const sinon = require('sinon');
+const ObjectID = require('bson-objectid').default;
+const configUtils = require('../../../../utils/configUtils');
+
+const LinkClickRepository = require('../../../../../core/server/services/link-tracking/LinkClickRepository');
+const {LinkClick} = require('@tryghost/link-tracking');
+
+const linkClicks = [
+    new LinkClick({
+        link_id: ObjectID(),
+        member_uuid: 'test-uuid'
+    }),
+    new LinkClick({
+        link_id: ObjectID(),
+        member_uuid: 'test-uuid'
+    })
+];
+
+describe('UNIT: LinkClickRepository class', function () {
+    let linkClickRepository;
+    let memberStub;
+    let memberLinkClickEventModelStub;
+    let memberLinkClickEventStub;
+    let domainEventsStub;
+
+    beforeEach(function () {
+        memberStub = {
+            findOne: sinon.stub()
+        };
+
+        memberLinkClickEventModelStub = {
+            add: sinon.stub()
+        };
+
+        memberLinkClickEventStub = {
+            create: sinon.stub()
+        };
+
+        domainEventsStub = {
+            dispatch: sinon.stub()
+        };
+
+        linkClickRepository = new LinkClickRepository({
+            MemberLinkClickEventModel: memberLinkClickEventModelStub,
+            Member: memberStub,
+            MemberLinkClickEvent: memberLinkClickEventStub,
+            DomainEvents: domainEventsStub
+        });
+    });
+
+    afterEach(function () {
+        sinon.restore();
+    });
+
+    describe('save', function () {
+        afterEach(function () {
+            configUtils.restore();
+        });
+
+        it('should save a link click event when member is found', async function () {
+            const member = {
+                id: 'member-id',
+                get: sinon.stub().returns('last-seen-at')
+            };
+
+            memberStub.findOne.resolves(member);
+            memberLinkClickEventModelStub.add.resolves({id: ObjectID().toHexString()});
+            // configStub.get.withArgs('linkClickTrackingCacheMemberUuid').returns(true);
+
+            await linkClickRepository.save(linkClicks[0]);
+
+            sinon.assert.calledOnce(memberStub.findOne);
+            sinon.assert.calledOnce(memberLinkClickEventModelStub.add);
+            sinon.assert.calledOnce(memberLinkClickEventStub.create);
+            sinon.assert.calledOnce(domainEventsStub.dispatch);
+        });
+
+        it('should not save a link click event when member is not found', async function () {
+            memberStub.findOne.resolves(null);
+            await linkClickRepository.save(linkClicks[0]);
+            sinon.assert.notCalled(memberLinkClickEventModelStub.add);
+            sinon.assert.notCalled(memberLinkClickEventStub.create);
+            sinon.assert.notCalled(domainEventsStub.dispatch);
+        });
+
+        it('should always call findOne when cacheMemberUuidLinkClick is false', async function () {
+            configUtils.set('linkClickTrackingCacheMemberUuid', false);
+            await linkClickRepository.save(linkClicks[0]);
+            sinon.assert.calledOnce(memberStub.findOne);
+            await linkClickRepository.save(linkClicks[1]);
+            sinon.assert.calledTwice(memberStub.findOne);
+        });
+
+        it('should use memoized findOne when cacheMemberUuidLinkClick is true', async function () {
+            configUtils.set('linkClickTrackingCacheMemberUuid', true);
+            await linkClickRepository.save(linkClicks[0]);
+            sinon.assert.calledOnce(memberStub.findOne);
+            await linkClickRepository.save(linkClicks[1]);
+            sinon.assert.calledOnce(memberStub.findOne);
+        });
+    });
+});