diff --git a/src/Pure/Admin/isabelle_devel.scala b/src/Pure/Admin/isabelle_devel.scala
--- a/src/Pure/Admin/isabelle_devel.scala
+++ b/src/Pure/Admin/isabelle_devel.scala
@@ -1,70 +1,71 @@
 /*  Title:      Pure/Admin/isabelle_devel.scala
     Author:     Makarius
 
 Website for Isabelle development resources.
 */
 
 package isabelle
 
 
 object Isabelle_Devel {
   val RELEASE_SNAPSHOT = "release_snapshot"
   val BUILD_LOG_DB = "build_log.db"
   val BUILD_STATUS = "build_status"
   val CRONJOB_LOG = "cronjob-main.log"
 
   val root: Path = Path.explode("~/html-data/devel")
   val cronjob_log: Path = root + Path.basic(CRONJOB_LOG)
 
 
   /* index */
 
   def make_index(): Unit = {
     val redirect = "https://isabelle-dev.sketis.net/home/menu/view/20"
 
     HTML.write_document(root, "index.html",
       List(
         XML.Elem(Markup("meta",
           List("http-equiv" -> "Refresh", "content" -> ("0; url=" + redirect))), Nil)),
       List(HTML.link(redirect, HTML.text("Isabelle Development Resources"))))
   }
 
 
   /* release snapshot */
 
   def release_snapshot(options: Options, rev: String, afp_rev: String,
     progress: Progress = new Progress
   ): Unit = {
     Isabelle_System.with_tmp_dir("isadist") { target_dir =>
       Isabelle_System.update_directory(root + Path.explode(RELEASE_SNAPSHOT),
         { website_dir =>
           val context = Build_Release.Release_Context(target_dir, progress = progress)
           Build_Release.build_release_archive(context, rev)
           Build_Release.build_release(options, context, afp_rev = afp_rev,
             build_sessions = List(Isabelle_System.getenv("ISABELLE_LOGIC")),
             website = Some(website_dir))
         }
       )
     }
   }
 
 
   /* maintain build_log database */
 
   def build_log_database(options: Options, log_dirs: List[Path]): Unit = {
     val store = Build_Log.store(options)
     using(store.open_database()) { db =>
+      db.vacuum()
       store.update_database(db, log_dirs)
       store.update_database(db, log_dirs, ml_statistics = true)
       store.snapshot_database(db, root + Path.explode(BUILD_LOG_DB))
     }
   }
 
 
   /* present build status */
 
   def build_status(options: Options): Unit = {
     Isabelle_System.update_directory(root + Path.explode(BUILD_STATUS),
       dir => Build_Status.build_status(options, target_dir = dir, ml_statistics = true))
   }
 }