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Re: OpenLDAP 2.4.15 : CSN too old when using 4-way multimaster
Le lundi 02 mars 2009 12:18:23, Howard Chu a écrit :
> Adrien Futschik wrote:
> > Considering that M1& M3 are on the same server and therefore have
> > exactly the same time, if this was a time related problem, I should'nt
> > get any "CSN too old" messages between M1&M3 and M2&M4, should I ?
> >
> > I have also noticed that when M1 gets a new entry and passes it to
> > M2&M3&M4, when M2&M3&M4 revieve it, they also pass it to M2&M3&M4 ! I
> > don't understand why this happends but it look's very much like this is
> > what's happening, because sometimes, M2 would have passed-it to M4,
> > before M4 has actualy revieved the add order from M1.
> >
> > I therefore happend to notice that sometimes, entries send from M1 are
> > revieved in the wrong ordrer by other masters and therefore some entries
> > may be skipped !!!
>
> Yes, that makes sense. The CSN check assumes changes will always be
> received in the same order they were sent from the provider. Obviously in
> this case this assumption is wrong. You should submit an ITS for this.
>
> This problem was discussed on the -devel list back in 2007; the code ought
> to be using a spanning tree/routing algorithm to ensure that when multiple
> routes exist for propagating a change, the change is delivered exactly
> once. Unfortunately no one has spent any further time on this issue since
> then.
I am not whethere it is M1 that sends them in the wrong order to M2 and then
cascaded to M3&M4, or if it is the order of M2 queue's that's wrong. I guess
this must be the second option.
I'll submit an ITS right away.
Personnaly I believe that the best way to avoid this problem to happen, would
be not to propagate entries just recieved from an other master.
Adrien Futschik