Per Steffensen skrev:
Hi
Due to what we have seen in recent tests I got in doubt how Solr
search is actually supposed to behave
* Searching with
"distrib=true&q=*:*&rows=10&collection=x,y,z&sort=timestamp asc"
** Is Solr supposed to return the 10 documents with the lowest
timestamp across all documents in all slices of collection x, y and z,
or is it supposed to just pick 10 random documents from those slices
and just sort those 10 randomly selected documents?
** Put in another way - is this search supposed to be consistent,
returning exactly the same set of documents when performed several
times (no documents are updated between consecutive searches)?
Fortunately I believe the answer is, that it ought to "return the 10
documents with the lowest timestamp across all documents in all slices
of collection x, y and Z". The reason I asked was because I got
different responses for consecutive simular requests. Now I believe it
can be explained by the bug described below. I guess they you do
cross-collection/shard searches, the "request-handling" Solr forwards
the query to all involved shards simultanious and merges sub-results
into the final result as they are returned from the shards. Because of
the "consider documents with same id as the same document even though
the come from different collections"-bug it is kinda random (depending
on which shards responds first/last), for a given id, what collection
the document with that specific id is taken from. And if documents with
the same id from different collections has different timestamp it is
random where that document ends up in the final sorted result.
So i believe this inconsistency can be explained by the bug described below.
* A search returns a "numFound"-field telling how many documents all
in all matches the search-criteria, even though not all those
documents are returned by the search. It is a crazy question to ask,
but I will do it anyway because we actually see a problem with this.
Isnt it correct that two searches which only differs on the
"rows"-number (documents to be returned) should always return the same
value for "numFound"?
Well I found out myself what the problem is (or seems to be) - see:
http://lucene.472066.n3.nabble.com/Changing-value-of-start-parameter-affects-numFound-td2460645.html
http://lucene.472066.n3.nabble.com/numFound-inconsistent-for-different-rows-param-td3997269.html
http://lucene.472066.n3.nabble.com/Solr-v3-5-0-numFound-changes-when-paging-through-results-on-8-shard-cluster-td3990400.html
Until 4.0 this "bug" could be "ignored" because it was ok for a
cross-shards search to consider documents with identical id's as dublets
and therefore only returning/counting one of them. It is still, in 4.0,
ok within the same collection, but across collections identical id's
should not be considered dublicates and should not reduce documents
returned/counted. So i believe this "feature" has now become a bug in
4.0 when it comes to cross-collections searches.
Created a issue/bug: SOLR-3765
Thanks!
Regards, Steff
