Re: Refactoring the checkpointer's fsync request queue

On Wed, Nov 14, 2018 at 4:49 PM Andres Freund <andres@anarazel.de> wrote:
> On 2018-11-14 16:36:49 -0500, Robert Haas wrote:
> > But how do you make reading that counter atomic with the open() itself?
>
> I don't see why it has to be. As long as the "fd generation" assignment
> happens before fsync (and writes secondarily), there ought not to be any
> further need for synchronizity?

If the goal is to have the FD that is opened first end up in the
checkpointer's table, grabbing a counter backwards does not achieve
it, because there's a race.

S1: open FD
S2: open FD
S2: local_counter = shared_counter++
S1: local_counter = shared_counter++

Now S1 was opened first but has a higher shared counter value than S2
which was opened later.  Does that matter?  Beats me!  I just work
here...

-- 
Robert Haas
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