So I'm looking at this patch in the commit fest. I have only a general
understanding of temporal query processing.
What this patch does is to add two new clauses for FROM-list items,
NORMALIZE and ALIGN, which reshuffle a set of ranges into a new list
that can then be aggregated more easily. From the original message:
> For NORMALIZE the tuples' ranges need to be split into all sub-ranges
> according to all matching ranges of the second relation. For this we
> create a subquery that first joins one relation with the range
> boundaries of the other and then sorts the result. The executor
> function splits the ranges in a sweep-line based manner.
>
> For ALIGN the tuples' ranges must be split into all intersections and
> differences with the other relation according to the join condition.
> For this we create a subquery that first joins the two relations and
> then sorts the result. The executor function splits the ranges
> accordingly in a sweep-line based manner.
So there isn't really temporal query processing as such here, only some
helpers that can make it easier.
I can see how those operations can be useful, but it would help if there
were a more formal definition to be able to check that further.
What I'm missing here is some references: existing implementations,
standards, documentation, research papers, alternative ideas, rejected
alternatives, etc.
Also, the submission is missing documentation and test cases. There are
technical terms used in the code that I don't understand.
I think there are probably many interesting applications for normalizing
or otherwise adjusting ranges. I'd like to see an overview and
consideration of other applications.
Ideally, I'd like to see these things implemented as some kind of
user-space construct, like an operator or function. I think we'd need a
clearer definition of what it is they do before we can evaluate that.
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services