Re: QT4CG meeting 148 draft minutes, 13 January 2026

Hi Christian,

The N-way merge is used when the N sorted lists are so big/long that they
cannot fit individually or together in the RAM of the computer.

In this case the N generators will be created using the *gn:make-generator*
function passing to it a provider that feeds it with one value at a time.
And in fact, any of the N different data sources can be of different type
(XML, JSON, etc) and have its own, unique data provider - all this is
configurable.

So, yes - if all the data is small and can fit into the RAM of the
computer, there is no reason why we would want to use the N-way merging.

The power of Generators is dealing with streaming data of unbounded volume.
This is why N-way merge is used as an essential part of external sorting.

>  I guess it may be simple (and more persuasive) to reformulate it in a
way that it works with infinite input? I tried for a while, but I failed.

Please, read about the *gn:make-generator
<https://qt4cg.org/pr/2247/xpath-functions-40/Overview.html#generator-make-generator>*
function and its protocol with its data-provider. Also see the examples to
it, and if there is something that is not clear, I would be glad to explain.

I would be glad to answer any other questions you or the people around you
might have.

Thanks,
Dimitre.

On Wed, Jan 14, 2026 at 3:21 AM Christian Grün <cg@basex.org> wrote:

> Hi Dimitre,
>
> > I really don't understand this statement. We have 138 examples/tests.
> Today's proposal had 5-6 examples, at least half of which deal with
> integers (even / odd/, etc.
>
> The proposal provides many examples, which are certainly helpful to
> understand what the specific functions are supposed to do. What we still
> miss (at least when I think of the feedback that I got from first reviewers
> and possible future users) are examples that demonstrate that (and how)
> generators will simplify tasks. An N-way merge could be a nice use case
> indeed. The current example can also be answered without generators and
> with a simple combination of join and sort:
>
>   array:sort(array:join(($ar1, $ar2, $ar3)))
>
> I guess it may be simple (and more persuasive) to reformulate it in a way
> that it works with infinite input? I tried for a while, but I failed.
>
> Best,
> Christian
>
>