* "Top K shouldn't start from the "start" parameter, if it does, it is a bug. "***
1. I clearly see that LTR do re-rank based on the start parameter. 2. When reRankDocs=24, pageSize=24, I still get the second page of results re-ranked by ltr plugin when I query with start=24. Alessandro Benedetti wrote > Are you using SolrCloud or any distributed search ? > > If you are using just a single Solr instance, LTR should have no problem > with pagination. > The re-rank involves the top K and then you paginate. > So if a document from the original score page 1 ends up in page 3, you > will > see it at page three. > have you verified that : "Say, if an item (Y) from second page is moved to > first page after > re-ranking, while an item (X) from first page is moved away from the first > page. ?" > Top K shouldn't start from the "start" parameter, if it does, it is a bug. > > The situation change a little with distributed search where you can > experiment this behaviour : > > *Pagination* > Let’s explore the scenario on a single Solr node and on a sharded > architecture. > > SINGLE SOLR NODE > > reRankDocs=15 > rows=10 > This means each page is composed by 10 results. > What happens when we hit the page 2 ? > The first 5 documents in the search results will have been rescored and > affected by the reranking. > The latter 5 documents will preserve the original score and original > ranking. > > e.g. > Doc 11 – score= 1.2 > Doc 12 – score= 1.1 > Doc 13 – score= 1.0 > Doc 14 – score= 0.9 > Doc 15 – score= 0.8 > Doc 16 – score= 5.7 > Doc 17 – score= 5.6 > Doc 18 – score= 5.5 > Doc 19 – score= 4.6 > Doc 20 – score= 2.4 > This means that score(15) could be < score(16), but document 15 and 16 are > still in the expected order. > The reason is that the top 15 documents are rescored and reranked and the > rest is left unchanged. > > *SHARDED ARCHITECTURE* > > reRankDocs=15 > rows=10 > Shards number=2 > When looking for the page 2, Solr will trigger queries to she shards to > collect 2 pages per shard : > Shard1 : 10 ReRanked docs (page1) + 5 ReRanked docs + 5 OriginalScored > docs > (page2) > Shard2 : 10 ReRanked docs (page1) + 5 ReRanked docs + 5 OriginalScored > docs > (page2) > > The the results will be merged, and possibly, original scored search > results > can top up reranked docs. > A possible solution could be to normalise the scores to prevent any > possibility that a reranked result is surpassed by original scored ones. > > Note: The problem is going to happen after you reach rows * page > > reRankDocs. In situations when reRankDocs is quite high , the problem will > occur only in deep paging. > > > > ----- > --------------- > Alessandro Benedetti > Search Consultant, R&D Software Engineer, Director > Sease Ltd. - www.sease.io > -- > Sent from: http://lucene.472066.n3.nabble.com/Solr-User-f472068.html ----- --Ilay -- Sent from: http://lucene.472066.n3.nabble.com/Solr-User-f472068.html
