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From "Shai Erera (JIRA)" <>
Subject [jira] [Commented] (LUCENE-4757) Cleanup FacetsAccumulator API path
Date Thu, 07 Feb 2013 06:23:13 GMT


Shai Erera commented on LUCENE-4757:

There are few abstractions that were added (compared to CountingFC), but I don't see why they
will slow things down:

* FacetsCollector.getFacetResult() delegates to FacetsAccumulator vs. CountingFC which does
the work on its own. Still, that's one method call for computing all the results.

* FacetsAccumulator calls FacetsAggregator to aggregate (count) the facets. That's one API
call, and CountingFC also calls a method to do that. One difference could be JIT - in CountingFC,
the method that's called is private, while FacetsAggregator is an interface. Since we don't
know when JIT kicks in and when not, we can't tell for sure that it's the cause. Still, I
could make CountingFacetsAggregator and FastCountingFacetsAggregator final, if that may help.
What do you think?

* FacetsAccumulator calls FacetResultsHandler to compute the top-K facets, where CountingFC
computed on its own (but still used a PQ class). That too is one method call, but same like
FacetsAggregator, may not be JIT-able. I made some improvements (patch to follow shortly)
where Int/FloatFacetResultsHandler are made final and FRHandler now takes FacetArrays in its
ctor, which means they can access final class members only. Perhaps that will help. It makes
FacetResultsHandler stateful, but the code now anyway initializes a new instance per FacetRequest
(which is a cheap instance).

The code now is more "structured" and clean. I can write a FastCountingFacetsAccumulator which
will go back to doing aggregation + top-K computation on its own, privately. But that starts
to get ugly ... not sure it's worth it for only 6%?
> Cleanup FacetsAccumulator API path
> ----------------------------------
>                 Key: LUCENE-4757
>                 URL:
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: modules/facet
>            Reporter: Shai Erera
>            Assignee: Shai Erera
>         Attachments: LUCENE-4757.patch, LUCENE-4757.patch
> FacetsAccumulator and FacetRequest expose too many things to users, even when they are
not needed, e.g. complements and partitions. Also, Aggregator is created per-FacetRequest,
while in fact applied per category list. This is confusing, because if you want to do two
aggregations, e.g. count and sum-score, you need to separate the two dimensions into two different
category lists at indexing time.
> It's not so easy to refactor everything in one go, since there's a lot of code involved.
So in this issue I will:
> * Remove complements from FacetRequest. It is only relevant to CountFacetRequest anyway.
In the future, it should be a special Accumulator.
> * Make FacetsAccumulator concrete class, and StandardFacetsAccumulator extend it and
handles all the stuff that's relevant to sampling, complements and partitions. Gradually,
these things will be migrated to the new API, and hopefully StandardFacetsAccumulator will
go away.
> * Aggregator is per-document. I could not break its API b/c some features (e.g. complement)
depend on it. So rather I created a new FacetsAggregator, with a bulk, per-segment, API. So
far migrated Counting and SumScore to that API.
> ** In the new API, you need to override FacetsAccumulator to define an Aggregator for
use, the default is CountingFacetsAggregator.
> * Started to refactor FacetResultsHandler, which its API was guided by the use of partitions.
I added a simple {{compute(FacetArrays)}} to it, which by default delegates to the nasty API,
but overridden by specific classes. This will get cleaned further along too.
> * FacetRequest has a .getValueOf() which resolves an ordinal to its value (i.e. which
of the two arrays to use). I added FacetRequest.FacetArraysSource and specialize when they
are INT or FLOAT, creating a special FacetResultsHandler which does not go back to FR.getValueOf
for every ordinal. I think that we can migrate other FacetResultsHandlers to behave like that
... at the expense of code duplication.
> ** I also added a TODO to get rid of getValueOf entirely .. will be done separately.
> * Got rid of CountingFacetsCollector and StandardFacetsCollector in favor of a single
FacetsCollector which collects matching documents, and optionally scores, per-segment. I wrote
a migration class from these per-segment MatchingDocs to ScoredDocIDs (which is global), so
that the rest of the code works, but the new code works w/ the optimized per-segment API.
I hope performance is still roughly the same w/ these changes too.
> There will be follow-on issues to migrate more features to the new API, and more cleanups

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