On the install requirements page (System Requirements - YaCy), it reckons you can run YaCy with a minimum of 256mb, which seems unrealistic.
On my system, originally trying to index my own small website with a depth of 3 and 4GB of ram, it kept crashing.
I gave it 6gb, started a new crawl with a depth of 10 and that still wasn’t enough.
I’ve now given it 20gb ram, and it seems to be coping at the moment.
I don’t understand why it needs so much RAM, as surely it doesn’t try to index everything at once???