[infinispan-dev] Query.getResultSize() to be available on the simplified DSL?

[Adrian Nistor]

I'd vote for keeping it, and executing it lazily in environments where 
it is costly to compute it upfront.

And off course, document this properly so users will be aware it can 
incur a second execution, with significant performance impact and also 
possibly a data visibility/consistency impact. I'd do this because the 
api is meant to be first of all user friendly and useful, not just 
machine friendly and efficient.

There's another reason for having it. Say we remove it, how will users 
be able to know the total number of matching results?  Our DSL does not 
currently have a 'count' function. Maybe we should add such a thing 
first, and then think about removing Query.getResultsSize().

But, if we implement a proper 'count', getResultsSize() could be 
trivially implemented as some kind of syntactic sugar on top of it, so I 
would still consider it worth being in the API.

And then it all boils down to the question: /should the DSL provide a 
count function?/ (+1 from me)

Cheers

On 03/10/2014 02:23 PM, Sanne Grinovero wrote:
> Hi all,
> we are exposing a nice feature inherited from the Search engine via
> the "simple" DSL version, the one which is also available via Hot Rod:
>
> org.infinispan.query.dsl.Query.getResultSize()
>
> To be fair I hadn't noticed we do expose this, I just noticed after a
> recent PR review and I found it surprising.
>
> This method returns the size of the full resultset, disregarding
> pagination options; you can imagine it fit for situations like:
>
>     "found 6 million matches, these are the top 20: "
>
> A peculiarity of Hibernate Search is that the total number of matches
> is extremely cheap to figure out as it's generally a side effect of
> finding the 20 results. Essentially we're just exposing an int value
> which was already computed: very cheap, and happens to be useful in
> practice.
>
> This is not the case with a SQL statement, in this case you'd have to
> craft 2 different SQL statements, often incurring the cost of 2 round
> trips to the database. So this getResultSize() is not available on the
> Hibernate ORM Query, only on our FullTextQuery extension.
>
> Now my doubt is if it is indeed a wise move to expose this method on
> the simplified DSL. Of course some people might find it useful, still
> I'm wondering how much we'll be swearing at needing to maintain this
> feature vs its usefulness when we'll implement alternative execution
> engines to run queries, not least on Map/Reduce based filtering, and
> ultimately hybrid strategies.
>
> In case of Map/Reduce I think we'll need to keep track of possible
> de-duplication of results, in case of a Teiid integration it might
> need a second expensive query; so in this case I'd expect this method
> to be lazily evaluated.
>
> Should we rather remove this functionality?
>
> Sanne
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