tdb_delete marking records as dead?

[tridge at samba.org]

Volker,

This looks good. I suspect it will help on some systems and is fairly
simple.

I suspect we'd gain more by splitting up the freelist into N
freelists, with a central freelist that is used to fill the other
freelists, but that would be a more complex patch, so going with this
simpler patch first is probably worthwhile.

It would be good to construct a benchmark that proves that this is a
win. Maybe a varient of tdbtorture would show it on a SMP system?

I suspect the other big win would be to use futexes (where
available). It isn't an easy API to use though.

Cheers, Tridge