Lock-free tdb lookups

[tridge at samba.org]

Joe,

 > I can't see any way of making things lock-free without infringing,
 > in part at least, on patent application 20050198030 "Efficient
 > support of consistent cyclic search with read-copy-update" by Paul
 > McKenney, file in March 2004,

I'd be pretty surprised if Paul's employer (IBM) wasn't happy to allow
that patent to be used in tdb. In Paul's talk at LCA last year I think
he specifically mentioned tdb as a possible use.

So I think the main impediment would be someone implementing it, and
proving its safe on all the architectures we care about. We'd also
have to decide if the extra complexity is worth it. If we find its
only a small gain then I'd rather keep the simple approach we have
now.

Also, with transactions there is very little locking going on anyway,
as the operations that happen within the transaction are lockless. 

Cheers, Tridge