tie %inv_index_db, $db_package, $INV_INDEX_DB_FILE, O_RDONLY, 0755 or die "Cannot open $INV_INDEX_DB_FILE: $!";   
tie %docs_db,      $db_package, $DOCS_DB_FILE, O_RDONLY, 0755 or die "Cannot open $DOCS_DB_FILE: $!";