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From "Robert Muir (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-4795) Add FacetsCollector based on SortedSetDocValues
Date Tue, 12 Mar 2013 04:43:13 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-4795?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13599699#comment-13599699
] 

Robert Muir commented on LUCENE-4795:
-------------------------------------

{quote}
I ask because it seems that the only thing that we get from this SortedSet approach is not
having to maintain a sidecar index (which for some reason freaks everybody), and we even lose
performance. Plus, I don't see how we can support other facet features with it. So perhaps
we should focus on how to use the search index to build a taxonomy? Maybe it's all in-memory,
that's fine. If we manage to support on-disk lookups too, even better. But if we do that,
then we should have no problems supporting all current facet features, because all that the
taxonomy index gives us is a global-ordinal (plus hierarchy management, but I think we can
do that w/ SortedSet too). We can of course explore that in a different issue.
{quote}

Well the taxonomy index doesn't give you global ordinals. it gives you global "termIDs", which
are unique integers: but they aren't ordinals: their sort order is meaningless. this creates
additional trouble if you want to try to integrate the current lucene facet module with e.g.
solr that has faceting options that rely upon these properties.

Its also unclear to me how the taxonomy index would really integrate in a distributed system
like solr or elasticsearch. I know there has been discussion about it before, and I'm sure
there are solutions, but it just seems fairly complicated. 

on the other hand SortedSet doesn't have these problems. maybe it doesnt support weighted
facets or other features, but its a nice option. I personally don't think its the end of the
world if Mike's patch doesnt support all the features of the faceting module initially or
even ever.

The idea is just to have more choices. I'm not saying you should get rid of the taxonomy index:
just provide options. I don't think lucene's faceting support needs to be limited to only
a single one-size-fits-all solution but instead have a few options with different tradeoffs.
Compare with something like the suggest module, it has like 5 or 6 implementations.

                
> Add FacetsCollector based on SortedSetDocValues
> -----------------------------------------------
>
>                 Key: LUCENE-4795
>                 URL: https://issues.apache.org/jira/browse/LUCENE-4795
>             Project: Lucene - Core
>          Issue Type: Improvement
>          Components: modules/facet
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>         Attachments: LUCENE-4795.patch, LUCENE-4795.patch, LUCENE-4795.patch, LUCENE-4795.patch,
pleaseBenchmarkMe.patch
>
>
> Recently (LUCENE-4765) we added multi-valued DocValues field
> (SortedSetDocValuesField), and this can be used for faceting in Solr
> (SOLR-4490).  I think we should also add support in the facet module?
> It'd be an option with different tradeoffs.  Eg, it wouldn't require
> the taxonomy index, since the main index handles label/ord resolving.
> There are at least two possible approaches:
>   * On every reopen, build the seg -> global ord map, and then on
>     every collect, get the seg ord, map it to the global ord space,
>     and increment counts.  This adds cost during reopen in proportion
>     to number of unique terms ...
>   * On every collect, increment counts based on the seg ords, and then
>     do a "merge" in the end just like distributed faceting does.
> The first approach is much easier so I built a quick prototype using
> that.  The prototype does the counting, but it does NOT do the top K
> facets gathering in the end, and it doesn't "know" parent/child ord
> relationships, so there's tons more to do before this is real.  I also
> was unsure how to properly integrate it since the existing classes
> seem to expect that you use a taxonomy index to resolve ords.
> I ran a quick performance test.  base = trunk except I disabled the
> "compute top-K" in FacetsAccumulator to make the comparison fair; comp
> = using the prototype collector in the patch:
> {noformat}
>                     Task    QPS base      StdDev    QPS comp      StdDev            
   Pct diff
>                OrHighLow       18.79      (2.5%)       14.36      (3.3%)  -23.6% ( -28%
-  -18%)
>                 HighTerm       21.58      (2.4%)       16.53      (3.7%)  -23.4% ( -28%
-  -17%)
>                OrHighMed       18.20      (2.5%)       13.99      (3.3%)  -23.2% ( -28%
-  -17%)
>                  Prefix3       14.37      (1.5%)       11.62      (3.5%)  -19.1% ( -23%
-  -14%)
>                  LowTerm      130.80      (1.6%)      106.95      (2.4%)  -18.2% ( -21%
-  -14%)
>               OrHighHigh        9.60      (2.6%)        7.88      (3.5%)  -17.9% ( -23%
-  -12%)
>              AndHighHigh       24.61      (0.7%)       20.74      (1.9%)  -15.7% ( -18%
-  -13%)
>                   Fuzzy1       49.40      (2.5%)       43.48      (1.9%)  -12.0% ( -15%
-   -7%)
>          MedSloppyPhrase       27.06      (1.6%)       23.95      (2.3%)  -11.5% ( -15%
-   -7%)
>                  MedTerm       51.43      (2.0%)       46.21      (2.7%)  -10.2% ( -14%
-   -5%)
>                   IntNRQ        4.02      (1.6%)        3.63      (4.0%)   -9.7% ( -15%
-   -4%)
>                 Wildcard       29.14      (1.5%)       26.46      (2.5%)   -9.2% ( -13%
-   -5%)
>         HighSloppyPhrase        0.92      (4.5%)        0.87      (5.8%)   -5.4% ( -15%
-    5%)
>              MedSpanNear       29.51      (2.5%)       27.94      (2.2%)   -5.3% (  -9%
-    0%)
>             HighSpanNear        3.55      (2.4%)        3.38      (2.0%)   -4.9% (  -9%
-    0%)
>               AndHighMed      108.34      (0.9%)      104.55      (1.1%)   -3.5% (  -5%
-   -1%)
>          LowSloppyPhrase       20.50      (2.0%)       20.09      (4.2%)   -2.0% (  -8%
-    4%)
>                LowPhrase       21.60      (6.0%)       21.26      (5.1%)   -1.6% ( -11%
-   10%)
>                   Fuzzy2       53.16      (3.9%)       52.40      (2.7%)   -1.4% (  -7%
-    5%)
>              LowSpanNear        8.42      (3.2%)        8.45      (3.0%)    0.3% (  -5%
-    6%)
>                  Respell       45.17      (4.3%)       45.38      (4.4%)    0.5% (  -7%
-    9%)
>                MedPhrase      113.93      (5.8%)      115.02      (4.9%)    1.0% (  -9%
-   12%)
>               AndHighLow      596.42      (2.5%)      617.12      (2.8%)    3.5% (  -1%
-    8%)
>               HighPhrase       17.30     (10.5%)       18.36      (9.1%)    6.2% ( -12%
-   28%)
> {noformat}
> I'm impressed that this approach is only ~24% slower in the worst
> case!  I think this means it's a good option to make available?  Yes
> it has downsides (NRT reopen more costly, small added RAM usage,
> slightly slower faceting), but it's also simpler (no taxo index to
> manage).

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