Re: [PATCHES] Lock

> [Charset ISO-8859-1 unsupported, filtering to ASCII...]
> > I was looking at this
> >
> > * Allow LOCK TABLE tab1, tab2, tab3 so all tables locked in unison
> >
> > but I'm not sure if my solution is really what was wanted, because it
> > doesn't actually guarantee an all-or-nothing lock, it just locks each
> > table in order. Thus it's more like a syntax simplification and reduces
> > overhead.
> >
>
> It took a few minutes, but I remember the use for this. If you are
> going to hang waiting to lock tab3, you don't want to lock tab1 and tab2
> while you are waiting for tab3 lock. The user wanted all tables to lock
> in one operation without holding locks while waiting to complete all
> locking.
>
> Can you do the locks, and if one fails, not hang, but unlock the
> previous tables, go lock/hang on the failure, and go back and lock the
> others? Seems it would have to be some kind of lock/fail/unlock/wait
> loop.

[CC to hackers]

Let me add to this. One problem is that my description would sometimes
lock the tables in different orders, and that is a recipe for deadlock.

If you have to release earlier locks to wait on a later lock, once you
get the later lock, you must release it and then start from the
beginning, locking them in order again. If you don't, the system could
report a deadlock at random times, which would be very bad.

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