Re: sinval synchronization considered harmful

Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Jul 21, 2011 at 6:43 PM, Noah Misch <noah@2ndquadrant.com> wrote:
>> On Wed, Jul 20, 2011 at 09:46:33PM -0400, Robert Haas wrote:
>>> SIGetDataEntries() can pretty easily be made lock-free.  The only real
>>> changes that seem to be are needed are (1) to use a 64-bit counter, so
>>> you never need to decrement

>> On second thought, won't this be inadequate on 32-bit systems, where updating
>> the 64-bit counter produces two stores?  You must avoid reading it between those stores.

> Now that is a potentially big problem.

Could we do something similar to the xxid hacks?  That is, we have a lot
of counters that should be fairly close to each other, so we store only
the low-order 32 bits of each notional value, and separately maintain a
common high-order word.  You probably would need some additional
overhead each time the high-order word bumps, but that's reasonably
infrequent.
        regards, tom lane