Do you have sync logging enabled?Log level is set to none, so the slapd log doesn't give much help.
Fix your log level.
In any case, with a server that large (3.5 million entries), I expect it will generally take a few months for it to catch up, since with standard syncrepl, it is going to try and refresh the entire database if it passed your sync ops log. I would strongly advise delta-syncrepl MMR instead, although that may take a significant amount of disk space for such a large DB if it is heavily active.The initial load of the directory via replication took < 2 days, so why would it take months to catch up? I tried restarting slapd with the -c flag specifying the current csn of the database, but it didn't seem to make any difference - is that expected? I'll take a look at using delta-syncrepl, since disk space isn't an issue.
Syncrepl is slow, and your database will have constant changes even while replication is ongoing -- So if in 2 days it is caught up to where the other servers were two days ago, it will have to go back through and restart comparisons. So it may take well under a month, the point is, it will take a significant amount of time. In addition, it is going to have to take changes from 4 servers, which may cause deadlocks and other issues in the DB, assuming you're using BDB as the backend.
--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