Re: ITS#8102, syncrepl concurrency

[ondra@mistotebe.net]

On Tue, May 12, 2015 at 07:27:22PM +0100, Howard Chu wrote:
> We should probably change the consumer such that when multiple
> consumers are configured on a context, only one of them can be
> active at a time. In particular, in refresh phase, you'll get
> multiple redundant copies of the refresh data. All providers should
> be equivalent, so whichever one we connect to first should be used
> and any others should be left idle.
>
> Or, each session should be established completely sequentially - do
> a complete refresh from provider #1, then do the same for provider
> #2, etc... In a quiescent setup, the refreshes after provider #1
> will be no-ops because the consumer is already up to date. In a busy
> setup, each refresh will still have work to do but it will be a
> smaller volume after provider #1's refresh completes.

Hi,
that should work just fine if you say "only one present/delete phase can
be active at a time*", once you receive the Sync Info Message, you can
start connecting to another provider. Or you might decide to stop at
that point, based on whether the DB is in MirrorMode. Stopping could
still break some exotic "MMR" topologies, though, not that I know of
anyone running them.

Also, if the olcSyncRepl directives are ordered correctly, the most
expensive phase would usually be served from a nearby provider.

* per suffix if you want to talk to one provider only

Cheers,
Ondra