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- To: firstname.lastname@example.org
- Subject: syncrepl
- From: Howard Chu <email@example.com>
- Date: Sun, 24 Dec 2006 14:58:26 -0800
- User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8b2) Gecko/20050318
ITS#4618, 4623, 4626 and 4703 all basically have to do with trying to
use multiple replication contexts with a single provider. This is a
behavior that the 2.3 syncprov implementation just wasn't designed for;
it was meant to handle only a single context.
Looking at the ideas in 2.2's syncrepl, it might have gone in the
direction of solving these problems if it weren't weighed down by so
many insurmountable design and implementation flaws. 2.2 probably tried
to do too much too soon, and got waylaid by the devil in the details.
At this point, this solution for multiple contexts presents itself:
1) We assign distinct searchbases to each context.
2) Every distinct source of changes must have its own unique rid. E.g.,
if a database is a provider for a context, it must have an rid. Every
consumer within its namingContext must have their own rid's just as
before. (The new requirement here is assigning rid's to providers that
are masters of their data.)
3) Currently the provider hands a consumer a cookie consisting of the
rid that the consumer supplied, plus a single contextCSN from the
provider. This single contextCSN is inadequate for accurately capturing
all of the changes that may come from multiple sources in a
namingContext. Instead, the provider will send out a cookie consisting
of multiple rid,CSN pairs - one for every rid of the provider's that
resides in the consumer's search space. This is the only reliable way to
make sure that all changes are tracked and propagated.
This says that in general, rids should not need to be configured on
consumers - they should be dictated solely by the providers. It may be a
good idea to allow them to be configured on consumers as an override,
but for now that seems unimportant.
1) the provider must have its own unique rid configured
2) the consumer's rid is optional
3) the provider must be told about all of the consumers living under it
4) the provider must aggregate all of the consumer cookies under it with
its own context info when generating a cookie for its own consumers
Currently slapd treats an entire database as read-only when it has a
consumer configured on it. This raises the question of how to allow
multiple consumers in a single context - should we allow multiple
consumers per DB, as 2.2 tried (and failed) to do, or should we continue
with the current approach of one consumer per DB, and use glue to
collect multiple consumers under one roof?
-- Howard Chu
Chief Architect, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc
OpenLDAP Core Team http://www.openldap.org/project/