Re: Rethinking stats communication mechanisms

I wrote:
> PFC <lists@peufeu.com> writes:
>> So, the proposal :
>> On executing a command, Backend stores the command string, then  
>> overwrites the counter with (counter + 1) and with the timestamp of  
>> command start.
>> Periodically, like every N seconds, a separate process reads the counter,  
>> then reads the data, then reads the counter again.

> BTW, I think the writer would actually need to bump the counter twice,
> once before and once after it modifies its stats area.  Else there's
> no way to detect that you've copied a partially-updated stats entry.

Actually, neither of these ideas works: it's possible that the reader
copies the entry between the two increments of the counter.  Then, it
won't see any reason to re-read, but nonetheless it has copied an
inconsistent partially-modified entry.

Anyone know a variant of this that really works?
        regards, tom lane