In order to determine which blocks have changed since the parent backup, the WAL files created from the time of the parent backup up to the start of the incremental backup are scanned by the WAL scanner program bart-scanner.The WAL scanner determines from the WAL files which blocks have been modified and records the information in a file called the modified block map (MBM) file. One MBM file is created for each WAL file.The MBM file is stored in the archive path directory backup_path/server_name/archived_wals where backup_path is the BART backup catalog parent directory specified in the global section of the BART configuration file and server_name is the lowercase conversion of the database server name specified for this database server in the server section of the BART configuration file. This is the same directory where the archived WAL files are stored in the BART backup catalog.The following is the content of the archive path showing the MBM files created for the WAL files. (The user name and group name of the files have been removed from the example to list the WAL files and MBM files in a more comparable manner.)In preparation for any incremental backup, the WAL files should be scanned as soon as they are copied to the BART backup catalog. Thus, the WAL scanner should be running as soon as the WAL files from the database cluster are archived to the BART backup catalog.If the BART backup catalog contains WAL files that have not yet been scanned, starting the WAL scanner begins scanning these files.Should a WAL file failed to be scanned resulting in a missing MBM file, the WAL scanner can be used to specify an individual WAL file to be scanned.Note: Under certain circumstances such as when the rsync utility is used to copy WAL files to the BART backup catalog, the WAL files may have been missed by the WAL scanner program for scanning and creation of MBM files. Use the scan_interval parameter in the BART configuration file to force scanning of WAL files in the archive directory of the BART backup catalog to ensure MBM files are generated. See sections 4.1, 4.2.5, and 5.5 for information.