thanks for your help. I read through the forum and found this entry:
Hi, Listary itself keeps the index in ram, and only read/write the index file when you start/close it. So it’s not necessary to move the index file to a ramdisk manually.
This would also explain why Listary.exe grabs about 260 MB RAM after starting. After stopping and restarting the program, I have an index file on disk. Because I have set Listary to start and stop with the OS, it probably deletes the file on shutdown, so I could not find it.