Keep startup database rebuilds out of memory

src/lib/server/db/connection.ts

@@ -2,7 +2,9 @@ import type Database from 'better-sqlite3';
 
 export function tuneConnection(handle: Database.Database, reader = false): void {
     handle.pragma(`cache_size = -${reader ? 32768 : 131072}`);
-    handle.pragma('temp_store = MEMORY');
+    // MEMORY also puts VACUUM's transient database in RAM. Disk-backed temps
+    // keep migrations and large sorts from growing with the entire database.
+    handle.pragma('temp_store = FILE');
     // mmap is opt-in because the controller data directory can be a network mount.
     const mmapMiB = Number(process.env.EC_SQLITE_MMAP_MB ?? 0);
     if (Number.isSafeInteger(mmapMiB) && mmapMiB >= 0 && mmapMiB <= 32768) {
@@ -10,3 +12,25 @@ export function tuneConnection(handle: Database.Database, reader = false): void
     }
     if (!reader) handle.pragma('journal_size_limit = 67108864');
 }
+
+/** Startup needs two page caches during VACUUM, plus buffers for legacy files. */
+export function tuneMigrationConnection(handle: Database.Database): void {
+    handle.pragma('cache_size = -16384');
+    handle.pragma('temp_store = FILE');
+    handle.pragma('mmap_size = 0');
+    handle.pragma('journal_size_limit = 67108864');
+}
+
+export function migrationStep<T>(name: string, work: () => T): T {
+    const started = Date.now();
+    console.info(`[database] migration starting: ${name}`);
+    try {
+        const result = work();
+        console.info(`[database] migration finished: ${name}`, { elapsedMs: Date.now() - started,
+            rssMiB: Math.round(process.memoryUsage().rss / 1048576) });
+        return result;
+    } catch (error) {
+        console.error(`[database] migration failed: ${name}`, error);
+        throw error;
+    }
+}