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Re: commit: ldap/servers/slapd syncrepl.c

Howard Chu wrote:
The basic idea is this - on the provider, set up an accesslog DB for logging changes, in addition to the main database. Set up the syncprov overlay on the logging DB, not the main DB. Thus syncrepl will be propagating full entries as usual, but the content of those entries will actually be deltas, not actual entries... A sample config looks like this:

database bdb
suffix cn=accesslog
directory db.1.b
rootdn cn=accesslog
rootpw secret
overlay syncprov
syncprov-nopresent TRUE

database bdb
suffix dc=example,dc=com
directory db.1.a
overlay accesslog
logdb cn=accesslog
logops writes
logsuccess TRUE # by default, accesslog logs failed requests too. we just want successful writes.

On the consumer, the configuration looks like:

database bdb
suffix dc=example,dc=com
syncrepl    rid=1

This separation of log info from syncprovider is rather troublesome; it won't fallback properly to a full refresh if the consumer is too far out of date wrt the log database.

A better implementation would be to leave the syncprovider overlay on top of the main database, and add a config keyword telling it where it can find a log database to use. Then both syncprov and accesslog overlays would sit on the main database. And ideally, there would be a new flag in the syncrepl control requesting that changes be propagated in commit order, as deltas instead of full entries.

I guess there are two directions to go here - first, the accesslog DB could be used by the sync provider as a non-volatile session log. That would allow it to work efficiently across server restarts.

Next, I'm considering a secondary consumer config specifically for the delta log. E.g.

The consumer can access the log in RefreshOnly or Persist mode; if the Provider signals that the consumer is out of date then the consumer will do a full refresh against the actual DB, and then return to using the log db.

 -- 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/