Re: question about window function in C

Well I'm trying to implement a window-function that works on range_types
and produces 'atomic ranges' for each input range.
Let's say I have a set of ranges some overlapping some not, and I want to
split each range at every boundary of every overlapping range and return
those.
So for each range r I want to return an array of ranges that consists of
range r split at every overlapping range boundary.
I need to consider both upper and lower boundaries and to be able to do
this in one pass over the data I need to sort both the upper and lower
boundaries and also sort the original ranges so I can loop over the ranges
and boundaries in lockstep to produce the arrays.
As a last step I sort back the arrays of atomic ranges in the original
order in the window so I can read out the tuplesort in that order and
return each array to its corresponding range r.

(The result can be used to answer questions like what are the maximum
number of simultaneously overlapping ranges and at which ranges the maximum
occurs)

Best Regards
Dan S

2014-12-26 18:57 GMT+01:00 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:

> Dan S <strd911(at)gmail(dot)com> writes:
> > I'm trying to write a window function in C .
> > In the function I'm using a tuplesort to sort the window data and then do
> > some processing.
>
> Hmm ... why do you feel you need to do that? The window function's input
> should already be sorted according to the window specification.
>
> > Now when I'm running the function I get this: 'WARNING: temporary file
> > leak: File 43 still referenced'
> > The warning comes from my failure to call tuplesort_end at the
> appropriate
> > time.
>
> Unsurprising.
>
> > So I think I need to use some callback mechanism to get that to work.
> > I've found some reference in the postgres source code to
> > RegisterExprContextCallback which seemed promising but I have no idea how
> > to get the right expression context to put in as the first argument to
> that
> > function.
>
> I don't think there is one :-(. WindowAgg has a per-input-tuple econtext,
> and a per-output-tuple econtext, but what you'd need for this is a
> partition-lifespan econtext, which doesn't exist.
>
> It's possible that we could promote the "partcontext" memory context into
> a full econtext so as to support this sort of behavior. But I'd want to
> see a reasonably convincing use-case for it.
>
> regards, tom lane
>