XnView Software

Even if the file with the category set no longer exists, the category information attached to the file deleted outside of xnview seems to remain. (Files that no longer exist are still counted in the catalog search category.)

However, even if I run Settings>Catalog>Maintenance, it is not reflected.

How can I synchronize with the current files (exising or not) status? Do I have to rescan using "Folder Sync" every time?

I have no idea how to do this because there is no explanation of the operation of each Setting menu or the difference in options.
It doesn't seem like there is an explanation of settings anywhere, but why doesn't this software ever try to maintain help?

It is not only categories that remain with information on nonexistent files, but also ratings and the like.
And they do not disappear even after maintenance is performed.
Example: 1. There are 1000 files with a rating of 1. 2.
2. Delete them from a folder other than xnviewMP (e.g. Explorer) or move them to an unmanaged folder.
3. select rating 1 in catalog search (global, recursive)
4. long loading runs. (During this time, it is displayed with default icons for files that do not exist.

If catalog maintenance is performed after 2., the files disappear after the loading is finished, but during the long loading, the non-existent files are still visible.

When the number of files is huge, such as 500,000 files, it takes a very long time to complete each search>loading.
I would like to do something about this.

This software is multifunctional and excellent, but this behavior significantly reduces its usefulness.

XnView can't know when a file is deleted outside.
you can use 'Catalog>Sync folders'

Good old Picasa used to be able to do just that, by comparing a previous FAT image (or other system allocation table) with the current FAT. It seems that small file search programs are also capable of reading FAT in a second...
This would be a major improvement for XnViewMp, but it requires rigorous (and configurable) management of the monitored folders.