[Pkg-openldap-devel] Bug#750022: slapd: offer mdb backend in configuration

[Ryan Tandy]

On 31/05/14 12:34 PM, Ryan Tandy wrote:
> The LMDB backend is now considered stable, and in 2.4.40 upstream will
> start to recommend it over hdb as the default backend. For jessie I'd
> like for it to at least be included as an option in the debconf menus.

Trivial example of how that might look (modulo a debconf-updatepo) attached.

> The default maxsize for back-mdb is 10 MiB, only enough (IMO) for a toy
> database. I think we should configure it higher, but I'm not sure how
> high. On 32-bit systems there is only so much address space available.

How about a default of 1 GiB? That should fit in the 32-bit address 
space but is still significantly larger than any casual user is likely 
to have. We should document the size restriction, though, and if 
possible provide an example of a cron job to monitor it.

> I predict, though, that offering mdb as a configuration choice is going
> to result in a lot of people asking for dpkg-reconfigure to be able to
> change the backend of an existing database (ie. #599585)...

Actually, AFAICT dpkg-reconfigure is happy to create a new database with 
a different backend. Will follow that bug up separately.

> I don't know what the format stability of mdb is like (ie. whether, or
> when, a dump/reload is required). I will look into that.

IIRC, in 2.4.40 there is a forward-incompatible change: upgrades to 
2.4.40 are fine but going back requires a reload. Can't find an ITS 
reference right now: might have been an IRC discussion (wishing I kept 
better logs) or maybe my brain is starting to invent things...

The disk format will not change backward-incompatibly in 2.4, but it 
sounds like it will at the transition to 2.5. ([ITS#7713] is an example 
of a format-breaking change.)

[ITS#7713] <http://www.openldap.org/its/?findid=7713>

Out of time for tonight and probably for the weekend, looking forward to 
Debconf where I might have some bigger blocks of time for this...

cheers,
Ryan
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