Question

I have written a custom request handler in solr to meet my business requirements. The handler involves getting data from two different from SolrIndexSearchers. I want the returned doclists from the two SolrIndexSearchers merged into one.

I tried iterating through one and adding doc by doc to another, but all I could get was an “Unsupported Operation” exception. Is there anyway to merge two doclists?

[Edit 1] : Code snippet inside the overridden handleRequestBody method

   SolrCore core = new SolrCore("Desired Directory 1", schema);
   reader = IndexReader.open("Desired Directory 1");
   searcher = new SolrIndexSearcher(core, schema, getName(), reader, false);
   Sort lsort = null;
   FilteredQuery filter = null;
   DocList results1 = searcher.getDocList(query, filter, lsort, 0, 10);
   reader.close();
   searcher.close();
   core.close();
   SolrCore core = new SolrCore("Desired Directory 2", schema);
   reader = IndexReader.open("Desired Directory 2");
   searcher = new SolrIndexSearcher(core, schema, getName(), reader, false);
   Sort lsort = null;
   FilteredQuery filter = null;
   DocList results2 = searcher.getDocList(query, filter, lsort, 0, 10);
   reader.close();
   searcher.close();
   core.close();
   rsp.add("response",results1);
   rsp.add("response",results2);

Now that I have two DocLists results1 and results2, how do I merge them?

[Edit 2] : The problem is not an exception/stack trace. When I add two responses, I get the results in two response sets when it is a single machine search. When it is a distributed search, I only get the distribution between response 1 of machine 1 and response 1 of machine 2. IN my understanding, only when I merge the responses to a single set, I will be able to get proper distribution. Hope I am understandable?

Answer 1

DocList is not supposed to be changed after you retrieve it from a search result.

I had the similar problem and, if I remember correctly, I used:

org.apache.solr.util.SolrPluginUtils.docListToSolrDocumentList

to convert DocList to SolrDocumentList, which extends ArrayList<SolrDocument>, which consequently supports add(SolrDocument).

So the worst case scenario (from the performance standpoint) is to convert the first DocList to SolrDocumentList and then loop through all other DocLists calling add on each doc.
You’ll have to test how efficient this approach is. I’m not Solr expert, but this is where I’d start testing.