FAQ
Hi Joel,

Although I solved this issue with a custom CollectorFactory, I also have a
solution that uses a PostFilter and and optional ValueSource.
Could you take a look at SOLR-5831 and see if I've got this right?

Thanks,
Peter


On Mon, Dec 23, 2013 at 6:37 PM, Joel Bernstein wrote:

Peter,

You actually only need the current score being collected to be in the
request context. So you don't need a map, you just need an object wrapper
around a mutable float.

If you have a page size of X, only the top X scores need to be held onto,
because all the other scores wouldn't have made it into that page anyway so
they might as well be 0. Because the QueryResultCache caches's a larger
window then the page size you should keep enough scores so the cached
docList is correct. But if you're only dealing with 150K of results you
could just keep all the scores in a FloatArrayList and not worry about the
keeping the top X scores in a priority queue.

During the collect hang onto the docIds and scores and build your scaling
info.

During the finish iterate your docIds and scale the scores as you go.

Set your scaled score into the object wrapper that is in the request
context before you collect each document.

When you call collect on the delegate collectors they will call the custom
value source for each document to perform the sort. Your custom value
source will return whatever the float value is in the request context at
that time.

If you're also going to run this postfilter when you're doing a standard
rank by score you'll also need to send down a dummy scorer to the delegate
collectors. Spend some time with the CollapsingQParserPlugin in trunk to
see how the dummy scorer works.

I'll be adding value source collapse criteria to the
CollapsingQParserPlugin this week and it will have a similar interaction
between a PostFilter and value source. So you may want to watch SOLR-5536
to see an example of this.

Joel












Joel Bernstein
Search Engineer at Heliosearch


On Mon, Dec 23, 2013 at 4:03 PM, Peter Keegan <peterlkeegan@gmail.com
wrote:
Hi Joel,

Could you clarify what would be in the key,value Map added to the
SearchRequest context? It seems that all the docId/score tuples need to be
there, including the ones not in the 'top N ScoreDocs' PriorityQueue
(score=0). If so would the Map be something like:
"scaled_scores",Map<Integer,Float> ?

Also, what is the reason for passing score=0 for documents that aren't in
the PriorityQueue? Will these docs get filtered out before a normal sort by
score?

Thanks,
Peter


On Thu, Dec 12, 2013 at 11:13 AM, Joel Bernstein <joelsolr@gmail.com>
wrote:
The sorting is going to happen in the lower level collectors. You need
a
value source that returns the score of the document being collected.

Here is how you can make this happen:

1) Create an object in your PostFilter that simply holds the current score.
Place this object in the SearchRequest context map. Update object.score as
you pass the docs and scores to the lower collectors.

2) Create a values source that checks the SearchRequest context for the
object that's holding the current score. Use this object to return the
current score when called. For example if you give the value source a
handle called "score" a compound function call will look like this:
sum(score(), field(x))

Joel










On Thu, Dec 12, 2013 at 9:58 AM, Peter Keegan <peterlkeegan@gmail.com
wrote:
Regarding my original goal, which is to perform a math function using
the
scaled score and a field value, and sort on the result, how does this
fit
in? Must I implement another custom PostFilter with a higher cost
than
the
scale PostFilter?

Thanks,
Peter


On Wed, Dec 11, 2013 at 4:01 PM, Peter Keegan <
peterlkeegan@gmail.com
wrote:
Thanks very much for the guidance. I'd be happy to donate a working
solution.

Peter


On Wed, Dec 11, 2013 at 3:53 PM, Joel Bernstein <
joelsolr@gmail.com
wrote:
SOLR-5020 has the commit info, it's mainly changes to
SolrIndexSearcher
I
believe. They might apply to 4.3.
I think as long you have the finish method that's all you'll need.
If
you
can get this working it would be excellent if you could donate
back
the
Scale PostFilter.


On Wed, Dec 11, 2013 at 3:36 PM, Peter Keegan <
peterlkeegan@gmail.com
wrote:
This is what I was looking for, but the DelegatingCollector
'finish'
method
doesn't exist in 4.3.0 :( Can this be patched in and are there
any
other
PostFilter dependencies on 4.5?

Thanks,
Peter


On Wed, Dec 11, 2013 at 3:16 PM, Joel Bernstein <
joelsolr@gmail.com
wrote:
Here is one approach to use in a postfilter

1) In the collect() method call score for each doc. Use the
scores
to
create your scaleInfo.
2) Keep a bitset of the hits and a priorityQueue of your top X
ScoreDocs.
3) Don't delegate any documents to lower collectors in the
collect()
method.
4) In the finish method create a score mapping (use the hppc
IntFloatOpenHashMap) with your top X docIds pointing to their
score,
using
the priorityQueue created in step 2. Then iterate the bitset
(also
created
in step 2) sending down each doc to the lower collectors,
retrieving
and
scaling the score from the score map. If the document is not
in
the
score
map then send down 0.

You'll have setup a dummy scorer to feed to lower collectors.
The
CollapsingQParserPlugin has an example of how to do this.




On Wed, Dec 11, 2013 at 2:05 PM, Peter Keegan <
peterlkeegan@gmail.com
wrote:
Hi Joel,

I thought about using a PostFilter, but the problem is that
the
'scale'
function must be done after all matching docs have been
scored
but
before
adding them to the PriorityQueue that sorts just the rows to
be
returned.
Doing the 'scale' function wrapped in a 'query' is proving
to
be
too
slow
when it visits every document in the index.

In the Collector, I can see how to get the field values like
this:
indexSearcher.getSchema().getField("field(myfield").getType().getValueSource(SchemaField,
QParser).getValues()

But, 'getValueSource' needs a QParser, which isn't
available.
And I can't create a QParser without a SolrQueryRequest,
which
isn't
available.

Thanks,
Peter


On Wed, Dec 11, 2013 at 1:48 PM, Joel Bernstein <
joelsolr@gmail.com
wrote:
Peter,

It sounds like you could achieve what you want to do in a
PostFilter
rather
then extending the TopDocsCollector. Is there a reason
why a
PostFilter
won't work for you?

Joel


On Tue, Dec 10, 2013 at 3:24 PM, Peter Keegan <
peterlkeegan@gmail.com
wrote:
Quick question:
In the context of a custom collector, how does one get
the
values
of
a
field of type 'ExternalFileField'?

Thanks,
Peter


On Tue, Dec 10, 2013 at 1:18 PM, Peter Keegan <
peterlkeegan@gmail.com
wrote:
Hi Joel,

This is related to another thread on function query
matching (
http://lucene.472066.n3.nabble.com/Function-query-matching-td4099807.html#a4105513
).
The patch in SOLR-4465 will allow me to extend
TopDocsCollector
and
perform
the 'scale' function on only the documents matching
the
main
dismax
query.
As you mention, it is a slightly intrusive design and
requires
that I
manage my own PriorityQueue (and a local duplicate of
HitQueue),
but
should
work. I think a better design would hide the PQ from
the
plugin.
Thanks,
Peter


On Sun, Dec 8, 2013 at 5:32 PM, Joel Bernstein <
joelsolr@gmail.com
wrote:
Hi Peter,

I've been meaning to revisit configurable ranking
collectors,
but
I
haven't
yet had a chance. It's on the shortlist of things I'd
like
to
tackle
though.



On Fri, Dec 6, 2013 at 4:17 PM, Peter Keegan <
peterlkeegan@gmail.com>
wrote:
I looked at SOLR-4465 and SOLR-5045, where it
appears
that
there
is
a
goal
to be able to do custom sorting and ranking in a
PostFilter.
So
far,
it
looks like only custom aggregation can be
implemented
in
PostFilter
(5045).
Custom sorting/ranking can be done in a pluggable
collector
(4465),
but
this patch is no longer in dev.

Is there any other dev. being done on adding custom
sorting
(after
collection) via a plugin?

Thanks,
Peter


--
Joel Bernstein
Search Engineer at Heliosearch


--
Joel Bernstein
Search Engineer at Heliosearch


--
Joel Bernstein
Search Engineer at Heliosearch


--
Joel Bernstein
Search Engineer at Heliosearch


--
Joel Bernstein
Search Engineer at Heliosearch

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