Robert, Jim, thanks for thinking out loud about dynamic allocation of shared memory. Very much appreciated.
On 08/23/2011 01:22 AM, Robert Haas wrote: > With respect to a general-purpose shared memory allocator, I think > that there are cases where that would be useful to have, but I don't > think there are as many of them as many people seem to think. I > wouldn't choose to implement this using a general-purpose allocator > even if we had it, both because it's undesirable to allow this or any > subsystem to consume an arbitrary amount of memory (nor can it fail... > especially in the abort path) and because a ring buffer is almost > certainly faster than a general-purpose allocator. I'm in respectful disagreement regarding the ring-buffer approach and think that dynamic allocation can actually be more efficient if done properly, because there doesn't need to be head and tail pointers, which might turn into a point of contention. As a side note: that I've been there with imessages. Those were first organized as a ring-bufffer. The major problem with that approach was the imessages were consumed with varying delay. In case an imessage was left there for a longer amount of time, it blocked creation of new imessages, because the ring-buffer cycled around once and its head arrived back at the unconsumed imessage. IIUC (which might not be the case) the same issue applies for snapshots. Regards Markus Wanner -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
