Paolo Rossi wrote:

...

PS: 4GB of RAM is probably not enough for a 20GB database, you won't be able to configure caches large enough to get decent search performance. I think 8GB would be a practical minimum here.

This is also my opinion, for good performances are not sufficient, but now the question is: 4GB are not enough to anyway, to run (slowly) similar huge server without coredump?

p.s. or maybe I missed something, somewhere... :P

What is your entry cache size? I suggest you set it to something small, like 100, during the slapcat test.