feat: do not lock until migrations are needed (#10170)

src/lib/server-impl.ts

@@ -1,7 +1,7 @@
 import stoppable, { type StoppableServer } from 'stoppable';
 import { promisify } from 'util';
 import version from './util/version.js';
-import { migrateDb, resetDb } from '../migrator.js';
+import { migrateDb, requiresMigration, resetDb } from '../migrator.js';
 import getApp from './app.js';
 import type MetricsMonitor from './metrics.js';
 import { createMetricsMonitor } from './metrics.js';
@@ -336,6 +336,7 @@ async function start(
         if (config.db.disableMigration) {
             logger.info('DB migration: disabled');
         } else {
+            if (await requiresMigration(config)) {
                 logger.info('DB migration: start');
                 if (config.flagResolver.isEnabled('migrationLock')) {
                     logger.info('Running migration with lock');
@@ -351,6 +352,9 @@ async function start(
                 }
 
                 logger.info('DB migration: end');
+            } else {
+                logger.info('DB migration: no migration needed');
+            }
         }
     } catch (err) {
         logger.error('Failed to migrate db', err);

src/migrator.ts

@@ -40,6 +40,28 @@ export async function migrateDb(
     });
 }
 
+export async function requiresMigration({
+    db,
+}: Pick<IUnleashConfig, 'db'>): Promise<boolean> {
+    return noDatabaseUrl(async () => {
+        const custom = {
+            ...db,
+            connectionTimeoutMillis: secondsToMilliseconds(10),
+        };
+
+        // disable Intellij/WebStorm from setting verbose CLI argument to db-migrator
+        process.argv = process.argv.filter((it) => !it.includes('--verbose'));
+        const dbm = getInstance(true, {
+            cwd: __dirname,
+            config: { custom },
+            env: 'custom',
+        });
+
+        const pendingMigrations = await dbm.check();
+        return pendingMigrations.length > 0;
+    });
+}
+
 // This exists to ease testing
 export async function resetDb({ db }: IUnleashConfig): Promise<void> {
     return noDatabaseUrl(async () => {