[Samba] Re: TDB locking overhead and performance...

[David Collier-Brown]

   Indeed: the real answer is to use fast primitives inside
your fcntl lock code (;-))

--dave

Jeremy Allison wrote:
> On Sun, Apr 23, 2006 at 04:27:21PM -0400, David Collier-Brown wrote:
> 
>>   You can always check for a dead process if you save the
>>pid of the process which holds the lock.  Alas, this
>>is a slow operation, involving calling kill(pid, 0),
>>two process switches and a return.  As you
>>do relinquish the processor, that's not actually
>>evil, but is it something that conceivably could slow
>>you as much as the fcntl (;-))
>>
>>  From some old measurements on my Sun, I **think** it's
>>faster than **my** fcntl... I really need to remeasure
>>with Solaris 10.
> 
> 
> There's always a race though. You can crash after
> you get the lock but before you write your own
> PID. It's not atomic - for that you need kernel
> support.
> 
> Jeremy.
> 

-- 
David Collier-Brown,         | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
davecb at spamcop.net           |                      -- Mark Twain
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