diff --git a/docs/configuration.rst b/docs/configuration.rst
index 771fe994..c972319c 100644
--- a/docs/configuration.rst
+++ b/docs/configuration.rst
@@ -402,11 +402,21 @@ Description File to store IDs of downloaded files in. Downloads of files
             already recorded in this archive file will be skipped_.
 
             The resulting archive file is not a plain text file but an SQLite3
-            database, as lookup operations are significantly faster when the
+            database, as either lookup operations are significantly faster or
+            memory requirements are significantly lower when the
             amount of stored IDs gets reasonably large.
 =========== =====
 
 
+extractor.*.archive-format
+--------------------------
+=========== =====
+Type        ``string``
+Example     ``"{id}_{offset}"``
+Description An alternative `format string`_ to build archive IDs with.
+=========== =====
+
+
 Extractor-specific Options
 ==========================
 
diff --git a/gallery_dl/util.py b/gallery_dl/util.py
index 8302d95a..fc1f57d4 100644
--- a/gallery_dl/util.py
+++ b/gallery_dl/util.py
@@ -549,7 +549,9 @@ class DownloadArchive():
         self.cursor = con.cursor()
         self.cursor.execute("CREATE TABLE IF NOT EXISTS archive "
                             "(entry PRIMARY KEY) WITHOUT ROWID")
-        self.keygen = (extractor.category + extractor.archive_fmt).format_map
+        self.keygen = (extractor.category + extractor.config(
+            "archive-format", extractor.archive_fmt)
+        ).format_map
 
     def check(self, kwdict):
         """Return True if item described by 'kwdict' exists in archive"""