Bruce Momjian <pgman@xxxxxxxxxxxxxxxx> writes: >> On Fri, Dec 23, 2005 at 11:04:50AM -0500, Tom Lane wrote: >>> It's not that easy --- in the MVCC world there simply isn't a unique >>> count that is the right answer for every observer. But the idea of >>> packaging a count(*) mechanism as an index type seems like it might be >>> a good one. > I think our TODO has a good summary of the issues: The point here was the idea that we might implement something like the delta-counts approach, but package it to look like a specialized index type --- as opposed to making the user create triggers and so on, which'd surely be a lot more error-prone to set up. Also, if it were an index type then it would be relatively straighforward to get the planner to recognize the availability of a substitute way of doing COUNT(*). We could do all this in other ways but it'd require more new infrastructure. The DELETE problem might kill the idea though. regards, tom lane
