Is there a way to clean the cache when, for example, a directory has been deleted?

The admin interface, has, on its front page a refresh database link (or what is known as garbage collection) which should accomplish what you are seeking. you can also manually delete the cached files in the cache directory to accomplish this same task using an FTP client

My admin page still counts the comments made on photos of already deleted directories. How can I reset that?

It's true, that's a bug - the comments are not deleted when albums are. Submit it to Trac and we'll take care of it.. someday...

I have several albums from early stages of zenphoto which have no date set (zp_albums.date). Right now, all new albums get their date from the exif of the first image. Is there any way to update these nulls automatically?

I was thinking of using the garbageCollect function in gallery class but still haven't figured out how to.

thanks!

jordi-kun:

The best way is to drop the mtime fields from the albums and images tables, then run upgrade. This will make all images look "new".

ant800:

You should do a database refresh. This should delete all orphaned comments.

zp:

Simplest way to clean the cache is to use FTP to delete all the items in it. Alternatively, running upgrade.php will clean the cache.