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Re: delta-syncrepl contextCSN update timing, schema checking
John Morrissey wrote:
To make a long story short, it seems that syncrepl doesn't update the
backend's contextCSN until it's processed its backlog? To check, I stopped
another consumer and let a backlog build, then started it at debuglevel
16384 and watched the backend's contextCSN with ldapsearch(1). contextCSN
didn't increment until the backlog was completely processed, even though I
could see the changes it was processing with ldapsearch(1) as soon as they
If a consumer processes replication without updating the backend's
contextCSN, it will try to re-process the same replication entries when it
starts up again, which will generally fail. This seems to leave one in a
bind, either having to manually determine the correct value for contextCSN
and update it manually, or remove the backend's data files and let syncrepl
rebuild them from scratch. If this assessment is correct, this behavior
doesn't seem desirable.
Your description of the behavior is correct. It's required to work that way
with regular syncrepl; it probably should work differently for delta-sync but
nobody pointed it out before.
In regular syncrepl the refresh phase does a regular LDAP search, whose
results are returned in whatever arbitrary order the database normally
retrieves things. Since that's pretty much guaranteed not to be the same as
the order in which changes were made, we can't update the contextCSN until all
of the changes have been received.
In delta-syncrepl the refresh is coming from the log, and unless somebody has
been explicitly mucking around in the log DB, the entries will always be
returned in order, so it's possible to update the contextCSN after each entry
has been received. But it's up to the provider to send the cookie with each
entry in this case, and the syncprov overlay doesn't really know the
difference between delta-sync and regular sync, so it doesn't do it.
You could file an ITS for this, but I don't think we'll be changing this in 2.3.
-- Howard Chu
CTO, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc/
Chief Architect, OpenLDAP http://www.openldap.org/project/