[RFC] Use mutexes by default in db_open()

[Amitay Isaacs]

On Sun, May 7, 2017 at 8:40 PM, Ralph Böhme via samba-technical <
samba-technical at lists.samba.org> wrote:

> On Sun, May 07, 2017 at 11:52:59AM +0200, Volker Lendecke wrote:
> > On Sun, May 07, 2017 at 08:23:40AM +0200, Ralph Böhme wrote:
> > > On Sat, May 06, 2017 at 02:15:27PM -0700, Jeremy Allison wrote:
> > > > On Mon, Apr 24, 2017 at 04:16:45PM +0200, Ralph Böhme via
> samba-technical wrote:
> > > > > Hi!
> > > > >
> > > > > Is there any reason not to use mutexes by default? Maybe for 4.7?
> > > >
> > > > Ping. Can you propose this as an official patch ?
> > >
> > > sure, but I'd like Volker, metze or Michael to ack this first.
> > >
> > > So... anyone?
> >
> > I don't see why we should not do this.
>
> ok, thanks for confirming!
>
> I'll add a whatsnew section and will resubmit the patchset once done.
>
> -slow
>
>
Will this also happen for clustered samba case?  In that case, CTDB should
also default to using mutexes.

Currently CTDB will attach with mutexes option only if
  - CTDB tunable TDBMutexEnabled is set to 1, and
  - Samba passes TDB_MUTEX_LOCKING flag to DB_ATTACH control

I would like to get rid of the need for clients to specify tdb_flags to
DB_ATTACH control.  As the tdb_flags are really determined by the database
model which is dictated by the attach control (DB_ATTACH or
DB_ATTACH_PERSISTENT).  I already have a set of patches that clean up tdb
flags calculation in CTDB and do not rely on tdb_flags being sent to attach
controls.

So when we change Samba to use mutexes by default, I prefer CTDB to use
mutexes by default also. This will mean changing the default value of the
tunable TDBMutexEnabled to 1.  Possibly deprecate the tunable.

Amitay.