Well, from 2.3 to 2.4 a change wouldn't be very surprising. This is 2.4.6
to 2.4.7, which may be more surprising.
I think we don't have too much 2.4.6 users currently and if we communicate the
change clearly enough we can afford such a change. I think similar to Michael
here, let's avoid the additional config setting and make the new index format
the default. My reason for this is, that the option only really makes sense
when using old 2.3 (and 2.4.6) databases, the options is of very low values
when creating new databases, I guess. (And you would have to explicitly set
it for a new database to be able to use ordered indexes).
It may be surprising in that it's not in keeping with RE22/23 practice,
but there are a lot of benefits here. If this is to make it into RE24 at
all, I'd want it to get into the train as early as possible (2.4.7?) and
agree with it being a default. Of course there will be no bugs -- but if
there are, I'd like them seen at more sites as they continue their 2.4
installations. As Ralf pointed out, 2.4 isn't often in production, so if
this is introduced as default in 2.4.7 we'll probably get a lot of free
testing from sites evaluating for RE23->RE24 transition.
Yes, this might be a bit painful for the early adopters. Is there any sort
of magic number or similar where slapd could bail out "sorry, please
slapindex" if given a RE23 format database? Then at least the FAQ-O-Matic
could point out "use 2.4.6 slapcat then upgrade again" or some other
concrete procedure.