clarified signature: PostgreSQL manages high-volume data, SQLite only sees small snapshots;

--- a/src/Pure/Admin/build_log.scala	Thu May 04 15:31:27 2017 +0200
+++ b/src/Pure/Admin/build_log.scala	Thu May 04 15:38:24 2017 +0200
@@ -675,7 +675,6 @@
 
     /* full view on build_log data */
 
-    // WARNING: This may cause performance problems, e.g. with sqlitebrowser
     val full_table: SQL.Table =
     {
       val columns = meta_info_table.columns ::: sessions_table.columns.tail
@@ -746,17 +745,15 @@
         ssh_close = true)
     }
 
-    def update_database(db: SQL.Database, dirs: List[Path], ml_statistics: Boolean = false)
+    def update_database(db: PostgreSQL.Database, dirs: List[Path], ml_statistics: Boolean = false)
     {
       write_info(db, Log_File.find_files(dirs), ml_statistics = ml_statistics)
 
-      if (db.isInstanceOf[PostgreSQL.Database]) {
-        List(Data.full_table, Data.pull_date_table)
-          .foreach(db.create_view(_))
-      }
+      db.create_view(Data.full_table)
+      db.create_view(Data.pull_date_table)
     }
 
-    def snapshot(db: PostgreSQL.Database, sqlite_database: Path,
+    def snapshot_database(db: PostgreSQL.Database, sqlite_database: Path,
       days: Int = 100, ml_statistics: Boolean = false)
     {
       Isabelle_System.mkdirs(sqlite_database.dir)

--- a/src/Pure/Admin/isabelle_cronjob.scala	Thu May 04 15:31:27 2017 +0200
+++ b/src/Pure/Admin/isabelle_cronjob.scala	Thu May 04 15:38:24 2017 +0200
@@ -153,7 +153,7 @@
     using(store.open_database())(db =>
     {
       store.update_database(db, database_dirs, ml_statistics = true)
-      store.snapshot(db, build_log_snapshot)
+      store.snapshot_database(db, build_log_snapshot)
     })
   }