I also used strace to catch the problem, but i did not find where the slapd write to disk. It seems, it comes via set up the futex write locks? I'm not a kernel programmer and the code from openldap is hard to read. But strace I use for several years to find errors, it was also the first choice for me, to find the error. It is not a normal file that will be written...
The DB is always read off disk into the BDB backing cache the very first time slapd is run (assuming back-bdb or back-hdb are your backends). I don't see any bug/issue here.
--Quanah -- Quanah Gibson-Mount Sr. Member of Technical Staff Zimbra, Inc A Division of VMware, Inc. -------------------- Zimbra :: the leader in open source messaging and collaboration