optimal mdb flags

["Paul B. Henson" <henson@acm.org>]

So if it's not obvious, we're working on migrating our openldap deployment
to mdb from hdb :), I apologize for the flurry of questions, this will be
the last, at least for today ;).

I'm trying to evaluate the optimal configuration for mdb; it seems like for
the most part you can just set maxsize and move on if you don't have
performance issues, but one flag I've seen frequently mentioned for
improving performance is writemap. This seems like a win all around, unless
there is some bug that results in erroneous writes into the mapped region,
in which case it could potentially cause major database corruption. For
those that have been running mdb in the field for a while, are you using
writemap? Have you ever run into any corruption because of it?

The other flag that seems to be popular is nometasync. As opposed to nosync,
which might cause loss of some number of transactions in case of a crash,
nometasync only risks one? And the benefit is that it is "slightly faster"?
Again, any recommendations from field experience on this? Also, if you do
enable it, do you need a checkpoint directive, or is that only necessary for
nosync?

Thanks.