diff --git a/lib/read_db_cache.php b/lib/read_db_cache.php
index d67fc48..6f58a99 100644
--- a/lib/read_db_cache.php
+++ b/lib/read_db_cache.php
@@ -82,21 +82,30 @@ function qdb_read_materialize_decrypted_db(): array {
     $memfd = qdb_memfd_write($decrypted);
     if ($memfd !== null) {
         [$fd, $path] = $memfd;
-        $pdo = qdb_read_open_sqlite_on_path($path, $sql, false);
-        return [$pdo, $path, $fd];
+        try {
+            $pdo = qdb_read_open_sqlite_on_path($path, $sql, false);
+            return [$pdo, $path, $fd];
+        } catch (Throwable $e) {
+            // memfd is filled but SQLite cannot open /proc/self/fd on this host.
+            qdb_close_fd($fd);
+        }
     }
 
-    $fallbackDir = QDB_UPLOADS_DIR . '/.private_read';
-    if (!is_dir($fallbackDir)) {
-        @mkdir($fallbackDir, 0700, true);
+    $snapshotPath = qdb_read_ram_snapshot_path();
+    if (file_put_contents($snapshotPath, $decrypted) === false) {
+        throw new Exception('Could not write read snapshot');
     }
-    $fallback = $fallbackDir . '/snap_' . getmypid() . '_' . bin2hex(random_bytes(4)) . '.sqlite';
-    if (file_put_contents($fallback, $decrypted) === false) {
-        throw new Exception('Could not write private read snapshot');
-    }
-    @chmod($fallback, 0600);
-    $pdo = qdb_read_open_sqlite_on_path($fallback, $sql, false);
-    return [$pdo, $fallback, -1];
+    @chmod($snapshotPath, 0600);
+    $pdo = qdb_read_open_sqlite_on_path($snapshotPath, $sql, false);
+    return [$pdo, $snapshotPath, -1];
+}
+
+/**
+ * RAM-backed snapshot path (tmpfs). One file per worker; overwritten on refresh.
+ */
+function qdb_read_ram_snapshot_path(): string {
+    $dir = is_writable('/dev/shm') ? '/dev/shm' : sys_get_temp_dir();
+    return $dir . '/qdb_read_' . getmypid() . '.sqlite';
 }
 
 /**
@@ -223,6 +232,8 @@ function qdb_read_open_sqlite_on_path(string $sqlitePath, string $schemaSql, boo
                 if ($bytes === false || file_put_contents($savePath, $bytes) === false) {
                     throw new Exception('Could not copy memfd DB for migration save');
                 }
+            } elseif (!is_file($savePath)) {
+                throw new Exception('Cannot persist migration from missing read snapshot');
             }
             $pdo->exec('PRAGMA wal_checkpoint(FULL);');
             qdb_save($savePath, $migrateLock);