process shared robust mutexes for tdb

[Volker Lendecke]

Hi!

Under

http://git.samba.org/?p=vl/samba.git/.git;a=shortlog;h=refs/heads/tdb

find my current work in progress to augment the fcntl locks
in tdb with mutexes for the freelist and hash chain locks.
The reason for this is that fcntl under load pretty much
collapses. I don't have exact results yet, but the initial
tests for tdbtorture are spectacular. One test went down
from 8m47.470s to 0m13.376s. The tdb_open_ex patches are far
from done. I am still thinking how to protect tdb with
mutexes from other use. The idea is that this scheme is only
used for highly contended tdb like locking.tdb where we
don't do transactions for example.

Comments?

Volker

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