[erlang-questions] How to extend mensia lock to support conditionally lock?

[devdoer bird]

2008/7/25, Ulf Wiger <ulf@REDACTED>:
>
> As far as I know there are no docs on the locker implementation
> in mnesia, but I do recall some tricky bugs in this area. For
> one thing, the locker also handles the deadlock prevention
> logic, so it must keep track of dependencies to some extent.
>
> You can read the code and try to form your own opinion,
> but before you start trying to extend this part of mnesia,
> possibly introducing deadlock bugs in your application,
> you should carefully measure the performance of the
> existing locking solutions: record locks, sticky locks
> and table locks. You should also write a wrapper and see
> if it gives you the kind of performance improvement you're
> after. If it doesn't, you may be able to come up with some
> really nifty extension of mnesia_locker through deep
> meditation over the code. The next challenge, after ensuring
> that it's stable, would then be to try to get it accepted as
> an official extension to mnesia - otherwise, you'll be stuck
> maintaining your own mnesia patches, and that's no fun
> (been there, done that).
>
> Table locks can be surprisingly efficient, esp if you don't
> mix record and table locks too much. I'd advice some
> experimentation down that alley first.


Thanks! I'll do some experiement  first .

BR,
> Ulf W
>
> BR,
> Ulf W
>
> 2008/7/24 devdoer bird <devdoer2@REDACTED>:
> >
> >
> >
> > 2008/7/24, Ulf Wiger <ulf@REDACTED>:
> >>
> >> If you are to gain any performance compared to a wrapper, or using
> >> only table locks, you must do brain surgery on  mnesia_locker. I
> >> strongly advise against that. The relationship between record locks
> >> and table locks is quite intricate.
> >
> >
> > Yes.I want to gain some performance to lock part of the table.
> > What's the intricate part of the locking system design?Can you give any
> docs
> > about the design of the mensia table-lock and record lock?
> >>
> >> BR,
> >> Ulf W
> >>
> >> 2008/7/24, devdoer bird <devdoer2@REDACTED>:
> >> > The example I give is not good.,but I just need hack the mnesia lock
> :(.
> >> >
> >> > I want to lock part of the table and which part is controled by the
> >> > record's
> >> > key's value range .Currently mnesia  only support record lock and
> table
> >> > lock.
> >> >
> >> >
> >> > 2008/7/24, Ulf Wiger <ulf@REDACTED>:
> >> >>
> >> >> I don't think you should hack mnesia for that. A simple wrapper
> >> >> function will do nicely.
> >> >>
> >> >> BR,
> >> >> Ulf W
> >> >>
> >> >> 2008/7/23, devdoer bird <devdoer2@REDACTED>:
> >> >> > HI:
> >> >> >
> >> >> > I want to extend mnesia 's lock  to add this  function
> >> >> > "mnesia:lock(LockItem,LockType,ConditionFun)" .
> >> >> >
> >> >> > This function works in this way: If a table 's record passes the
> >> >> > ConditionFun test,the the record is locked.
> >> >> >
> >> >> > Eg.
> >> >> > I have a user table with the record:  -record(user,{name,age}).
> >> >> >
> >> >> > I want to lock the user's whose name  begines with  'a' ,I can code
> >> >> > using
> >> >> my
> >> >> > customized " mnesia:lock(LockItem,LockType,ConditionFun)"
> >> >> >
> >> >> > like this:
> >> >> >
> >> >> > ConditionFun=fun(U)->
> >> >> >        if
> >> >> >             U#user.name=='a' -> true;
> >> >> >             true->false
> >> >> >        end
> >> >> > end
> >> >> > mnesia:lock(user,write,ConditionFun).
> >> >> >
> >> >> > that is I want to lock part of the table.
> >> >> >
> >> >> > Have anyone done this before? How shall I extend the mensia lock?
> Any
> >> >> > information will be  helpful, I 'm quite unfamiliar  with mnesia
> lock
> >> >> > system.
> >> >> >
> >> >>
> >> >
> >
> >
>
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