Product analytics on Next.js 16 (App Router), MySQL 8 and Clerk

Next.js 16 App Router: file-based routing, server components, and the Edge proxy (Next 16's renamed middleware).

MySQL 8 via Drizzle ORM and the mysql2 driver.

Clerk: hosted identity (sign-in UI, sessions, user management) mounted via middleware + provider.

Product-analytics schema: tracked apps with unique ingest keys, an append-only event stream, session windows, and saved funnels, all hung off Better Auth's user table.

Database client

import { drizzle } from "drizzle-orm/mysql2";
import mysql from "mysql2/promise";

// ponytail: single module-level pool; the runtime + mysql2's pool handle concurrency,
// so no globalThis singleton dance needed.
const pool = mysql.createPool(process.env.DATABASE_URL!);

export const db = drizzle({ client: pool });

// ponytail: Clerk is hosted — set NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY and
// CLERK_SECRET_KEY in the env. The publishable key is read client-side by
// <ClerkProvider>; the secret key is read server-side by clerkMiddleware().
// Both are picked up from the environment automatically — no wiring needed.

owner-scoped app registrations, each with a unique api_key used to authenticate inbound event writes

the raw, immutable event stream keyed by app and timestamp, with freeform JSON properties and an optional anonymous visitor id

visitor session windows (start/end timestamps) correlated to events via anonymous_id, with nullable ended_at for open sessions

saved multi-step funnel definitions stored as JSON steps arrays, scoped per tracked app

Auth runs in proxy.ts (Next 16's renamed middleware) on the Edge runtime: it gates on the session cookie's presence only — full session validation happens in Server Components and route handlers, not in the proxy.

mysql2's pool multiplexes connections; drizzle-orm/mysql2 wraps it. One module-level pool is right for a serverless/edge app — the runtime and the pool handle concurrency.

MySQL has no row-level security: multi-tenant isolation is enforced in application code via the forOrg helper (src/lib/tenant.ts), not by the database. See the tenant-scoping section on SaaS pages.

Hosted: Clerk owns identity and does NOT create a local `user` table. Store `clerk_user_id` as text without a foreign key, or sync Clerk users into a local table via webhook before relying on FKs to `user`.

Route protection is clerkMiddleware() + auth.protect() in the Next proxy (getAuth() in a React Router loader, or event.context.auth() on Nuxt) — logged-out users bounce to Clerk's hosted sign-in, so there are no self-hosted auth pages to build or maintain.

Keeping the local mirror in sync is a webhook job: a svix-verified webhook route replays user.created / user.updated / user.deleted idempotently into the local `user` row, so app-type foreign keys to `user` resolve even though Clerk is the source of truth.

ClerkProvider (client) wraps the app so the hosted <SignIn/> / <UserButton/> components and hooks work; the publishable key is read client-side, while the secret key is only ever read server-side by clerkMiddleware.

api_key on tracked_apps carries a unique constraint: each app gets exactly one ingest key, and the key is the authentication surface for the event ingestion endpoint.

events is append-only (no update path, no status column) — the composite index on (app_id, occurred_at) is the only query handle; roll-up queries must scan that index, not mutate rows.

Clerk is a hosted identity provider and does not create a local `user` table. This schema's foreign keys to `user` assume a local identity table (as Better Auth provides). With Clerk, store `clerk_user_id` as a text column without a foreign key, or sync Clerk users into a local `users` table via webhook before relying on these FKs.

MySQL provides no row-level security. On MySQL, multi-tenant isolation is APP-ENFORCED via the forOrg helper (src/lib/tenant.ts), not database-enforced like Postgres RLS. Every org-scoped query MUST go through forOrg — a missed query leaks across tenants. Postgres cells enforce this in the database itself (RLS), so it holds even for a query that forgets to scope.

Product analytics

Ingest is the constraint everything else bends around. A write arrives carrying an api_key, and that column on tracked_apps is UNIQUE so the lookup is a single index probe returning an app_id — no join to identity on the write path, even though tracked_apps.owner_id foreign-keys Better Auth's user table for the dashboard side. Every other table hangs off that app id: events, sessions and funnels all reference tracked_apps.id with ON DELETE cascade, which makes an app registration the unit of scoping and the unit of deletion at once. events.occurred_at is notNull with no default, and that is the schema's most consequential line. The caller stamps the event; the database does not.

An SDK buffering through a dead network replays honestly because the backlog keeps its real instants — and there is no received-at column anywhere, so nothing records how late a batch showed up. Properties travel in a JSON column with no declared shape and no index, so a filter on a property value runs inside whatever slice idx_event_app_time (app_id, occurred_at) has already narrowed. sessions is not the parent of events. Nothing foreign-keys the two together; the correlation is anonymous_id, which is notNull on sessions, nullable on events, and indexed on neither, while idx_session_app covers app_id alone. Per-app, per-window questions are therefore cheap and stitching one visitor's path is not: bound by app and time first, then match ids inside that slice.

If visitor-level replay is the product rather than a report, add an index on (app_id, anonymous_id, occurred_at) before the event table gets large, because the schema will not do it for you. funnels stores definitions, not results — a name and a JSON steps array per app, with no index declared beyond the primary key. Evaluating a three-step funnel is three bounded scans of idx_event_app_time with a name filter applied inside each, and nothing caches the answer. That keeps funnel maintenance off the write path entirely and puts the whole cost on read, which is the right trade while an app's volume still fits a range scan and the wrong one once it does not.

Next.js 16 (App Router)

Next 16's App Router keeps the whole application under src/: the scaffold runs create-next-app with --src-dir and --import-alias @/*, so `@/` resolves to src/* and the verified files land on top of a stock project rather than replacing it. initCode writes the database client to src/lib/db.ts, then appends the auth fragment's own files — identity tables at src/db/auth-schema.ts, the auth instance at src/lib/auth.ts, a catch-all handler under src/app/api/auth/, and src/proxy.ts. Each file has exactly one owner; the framework never re-emits the ones auth brought. Server code has two shapes here and they are not interchangeable. A Server Component runs on the server and imports { db } from "@/lib/db" directly, so a page can await a Drizzle query with no API route in between.

Anything that needs a URL — an OAuth callback, a Polar or Clerk webhook, a mutation posted from the client — is a route handler at src/app/api/<path>/route.ts exporting GET or POST. Session checking is split across two tiers on purpose. src/proxy.ts (Next 16's rename of middleware.ts; under --src-dir it must sit beside src/app or Next silently ignores it) runs on the Edge runtime with a config.matcher listing the guarded prefixes — /dashboard/:path* and /settings/:path* out of the box. It only asks whether a session cookie exists and redirects to /sign-in when it does not: no database round trip at the edge. The authoritative check is auth.api.getSession() inside the Server Component or route handler that actually reads rows.

What that means when you build on it: widening the protected surface is a one-line change to the matcher array, but the proxy is not the security boundary — a request carrying any session cookie reaches the page, and the page decides. Keep the real check next to the data. The UI overlay follows the same split, with auth screens under src/app/(auth)/ and the shell and dashboard under src/app/(app)/.

MySQL 8

MySQL 8 here is the mysql2 driver under Drizzle's mysql-core dialect: drizzle({ client: pool }) over one module-level mysql.createPool(DATABASE_URL). mysql2's pool multiplexes connections itself, so a single pool per module is the right shape — the runtime and the pool handle concurrency, with no globalThis singleton needed. The framework decides where that file lands (src/lib/db.ts on Next, app/lib/db.ts on React Router, server/lib/db.ts on Nuxt); the client text is the same in all three. The dialect's constraints show up directly in the column types.

MySQL cannot index a TEXT column without a prefix length, so anything that is a primary key, a UNIQUE, an index or a CHECK target is varchar with a declared length: ids are varchar(36) with no database default — the application generates them with crypto.randomUUID(), since there is no uuid type and no defaultRandom() — Better Auth's user.id and every FK pointing at it are varchar(255), an email or slug is varchar(255), a role or status varchar(32), a SHA-256 hex digest varchar(64). Free-form columns nobody indexes stay text. Timestamps are plain timestamp().defaultNow() without the withTimezone flag the Postgres bodies carry, and counters are bigint({ mode: "number" }). The operational difference that matters most: MySQL has no row-level security.

There is no policy layer to fall back on, so multi-tenant isolation is enforced in application code by forOrg(db, orgId) in src/lib/tenant.ts, which wraps each org-owned table's select/update/delete with a where on organization_id and throws on a missing orgId instead of quietly running unscoped. It is a real boundary only while every read and write goes through it — the shared plans catalog sits deliberately outside — and it is app-enforced, not database-enforced. Connections change with the deploy target: connectionLimit 2 per short-lived serverless instance, 10 in a long-running Node process, and on Cloudflare Workers mysql2 cannot run at all — there are no TCP sockets — so the edge client swaps to @planetscale/database over HTTP with drizzle-orm/planetscale-serverless.

Clerk

Clerk keeps identity on its own servers. The emitted app has no auth instance, no password column and no session table: the card at /sign-in is Clerk's <SignIn/> component rendered under a [[...sign-in]] catch-all so Clerk can mount its own verification and SSO-callback sub-routes there, and the endpoints behind it belong to Clerk. What does land in your database is a single mirror table. db/auth-schema.ts declares user with id set to the Clerk user id (text; varchar(255) on MySQL, so the app-type FK columns match exactly), plus email, first and last name, image URL, and an updated_at column used purely as a staleness key. It exists so app-type schemas can foreign-key user the way they would under a self-hosted auth.

It is not a source of truth, and application code should never write to it. Filling that mirror is a webhook job, and this fragment emits the whole path. lib/identity/record.ts holds recordClerkEvent; the mount is a Next route handler at src/app/api/webhooks/clerk/route.ts, an action in app/routes/webhooks.clerk.ts on React Router, or a Nitro .post.ts handler on Nuxt. Clerk delivers through svix, so the route verifies the raw body against CLERK_WEBHOOK_SECRET before anything reaches the database, and the record core is written for a delivery channel that retries and reorders: the staleness comparison lives inside the UPDATE's WHERE clause so an older event cannot clobber newer state, the insert path absorbs a concurrent duplicate (onConflictDoNothing on Postgres, an ER_DUP_ENTRY catch on MySQL), and user.deleted removes the row. Session checks never touch your Postgres.

Next's proxy.ts runs clerkMiddleware() and calls auth.protect() for anything matching createRouteMatcher(["/dashboard(.*)", "/settings(.*)"]); Nuxt reads event.context.auth() inside a Nitro middleware that the @clerk/nuxt module populates. Even the package name is framework-specific — @clerk/nextjs, @clerk/react-router, @clerk/nuxt — which upstreamPkgFor resolves per cell. The trade is concrete. You never build, style or maintain auth screens, and breaking changes arrive with Clerk's releases rather than your lockfile. In exchange, your user rows are eventually consistent with someone else's database, and a webhook you never configured is a table of missing foreign-key targets that only shows up when an app-type insert fails.