On 12/05/2013 06:32 AM, Robert Haas wrote:
During development of the dynamic shared memory facility, Noah and I spent a lot of time arguing about whether it was practical to ensure that a dynamic shared memory segment got mapped at the same address in every backend that used it.
My vote goes for not trying to map at same address. I don't see how you could do that reliably, and I don't see much need for it anyway.
That said, it naturally depends on what you're going to use the dynamic shared memory facility for. It's the same problem I have with reviewing the already-committed DSM patch and the message queue patch. The patches look fine as far as they go, but I have the nagging feeling that there are a bunch of big patches coming up later that use the facilities, and I can't tell if the facilities are over-engineered for what's actually needed, or not sufficient.
As a side-note, I've been thinking that we don't really need same-address mapping for shared_buffers either. Getting rid of it wouldn't buy us anything right now, but if we wanted e.g to make shared_buffers changeable without a restart, that would be useful.
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