On 02/05/2016 08:49 PM, Tom Lane wrote:

Yeah, I agree that a GUC for this is quite unappetizing.


One idea would be to build a hashtable to aid with duplicate detection
(perhaps only once the pending-notify list gets long).

Another thought is that it's already the case that duplicate detection is
something of a "best effort" activity; note for example the comment in
AsyncExistsPendingNotify pointing out that we don't collapse duplicates
across subtransactions.  Would it be acceptable to relax the standards
a bit further?  For example, if we only checked for duplicates among the
last N notification list entries (for N say around 100), we'd probably
cover just about all the useful cases, and the runtime would stay linear.
The data structure isn't tremendously conducive to that, but it could be


I like the hashtable idea if it can be made workable.



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