fix: fix too many clients error on Postgres due to HMR with Drizzle (t…

…3-oss#1766)

Co-authored-by: Julius Marminge <[email protected]>

.changeset/grumpy-avocados-eat.md

@@ -0,0 +1,5 @@
+---
+"create-t3-app": patch
+---
+
+fix: cache database connection during development to prevent `Too many connections` due to HMR

cli/template/extras/src/server/db/index-drizzle/with-mysql.ts

@@ -1,12 +1,18 @@
 import { drizzle } from "drizzle-orm/mysql2";
-import mysql from "mysql2/promise";
+import { createPool, type Pool } from "mysql2/promise";
 
 import { env } from "~/env";
 import * as schema from "./schema";
 
-export const db = drizzle(
- mysql.createPool({
- uri: env.DATABASE_URL,
- }),
- { schema, mode: "default" }
-);
+/**
+ * Cache the database connection in development. This avoids creating a new connection on every HMR
+ * update.
+ */
+const globalForDb = globalThis as unknown as {
+ conn: Pool | undefined;
+};
+
+const conn = globalForDb.conn ?? createPool({ uri: env.DATABASE_URL });
+if (env.NODE_ENV !== "production") globalForDb.conn = conn;
+
+export const db = drizzle(conn, { schema, mode: "default" });

cli/template/extras/src/server/db/index-drizzle/with-postgres.ts

@@ -4,4 +4,15 @@ import postgres from "postgres";
 import { env } from "~/env";
 import * as schema from "./schema";
 
-export const db = drizzle(postgres(env.DATABASE_URL), { schema });
+/**
+ * Cache the database connection in development. This avoids creating a new connection on every HMR
+ * update.
+ */
+const globalForDb = globalThis as unknown as {
+ conn: postgres.Sql | undefined;
+};
+
+const conn = globalForDb.conn ?? postgres(env.DATABASE_URL);
+if (env.NODE_ENV !== "production") globalForDb.conn = conn;
+
+export const db = drizzle(conn, { schema });

cli/template/extras/src/server/db/index-drizzle/with-sqlite.ts

@@ -4,9 +4,16 @@ import { drizzle } from "drizzle-orm/better-sqlite3";
 import { env } from "~/env";
 import * as schema from "./schema";
 
-export const db = drizzle(
- new Database(env.DATABASE_URL, {
- fileMustExist: false,
- }),
- { schema }
-);
+/**
+ * Cache the database connection in development. This avoids creating a new connection on every HMR
+ * update.
+ */
+const globalForDb = globalThis as unknown as {
+ conn: Database | undefined;
+};
+
+export const conn =
+ globalForDb.conn ?? new Database(env.DATABASE_URL, { fileMustExist: false });
+if (env.NODE_ENV !== "production") globalForDb.conn = conn;
+
+export const db = drizzle(conn, { schema });