SOLR-17319 : Combined Query Feature for Multi Query Execution #3418

ercsonusharma · 2025-07-04T09:19:21Z

https://issues.apache.org/jira/browse/SOLR-17319

Description

This feature aims to execute multiple queries of multiple kinds across multiple shards of a collection and combine their result basis an algorithm (like Reciprocal Rank Fusion). It also help resolve the issues being discussed w.r.t the previous PR, mainly around across shard documents merging. It provides more flexibility in terms of querying extending JSON Query DSL ultimately enabling Hybrid Search in a pure way solving the shortcomings.

Note: This feature is currently unsupported for non-distributed and grouping query.

Solution

Extended the QueryComponent to create new CombinedQueryComponent and ResponseBuilder to create new CombinedQueryResponseBuilder supports multiple response builders to hold the state and execute multiple queries.
In JSON Query DSL, a parameter is added to identity Combined Query request and basis that it invokes the new CombinedQueryComponent
CombinedQueryComponent have multiple response builders assigned for each query. These queries are first executed at the SolrSearchIndexer level and combined them using RRF for now.
At Shard level also, the responses for the multiple queries are merged.

Tests

Added tests for testing the RRF logic independently.
Added tests for across search index and distributed requests.
Added tests to assert existing behaviour of search handler's QueryComponent as well as for the newly added CombinedQueryComponent basis the flag in json query DSL.

Checklist

Please review the following and check all that apply:

I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
I have created a Jira issue and added the issue ID to my pull request title.
I have given Solr maintainers access to contribute to my PR branch. (optional but recommended, not available for branches on forks living under an organisation)
I have developed this patch against the main branch.
I have run ./gradlew check.
I have added tests for my changes.
I have added documentation for the Reference Guide

solr/core/src/java/org/apache/solr/handler/component/CombinedQueryComponent.java

solr/core/src/java/org/apache/solr/handler/component/QueryComponent.java

solr/core/src/java/org/apache/solr/handler/component/CombinedQueryComponent.java

ercsonusharma · 2025-07-09T17:21:12Z

@alessandrobenedetti @dsmiley, please help review it whenever you can. Thanks!

solr/core/src/java/org/apache/solr/handler/component/CombinedQueryComponent.java

solr/core/src/java/org/apache/solr/handler/component/combine/ReciprocalRankFusion.java

solr/core/src/java/org/apache/solr/search/combine/QueryAndResponseCombiner.java

solr/core/src/java/org/apache/solr/handler/component/SearchHandler.java

solr/core/src/test/org/apache/solr/handler/component/CombinedQueryComponentTest.java

solr/core/src/java/org/apache/solr/search/combine/ReciprocalRankFusion.java

dsmiley

Really glad to see this work began by acknowledging the existing work and trying to address the pitfalls!

solr/core/src/java/org/apache/solr/handler/component/QueryComponent.java

solr/core/src/java/org/apache/solr/handler/component/SearchHandler.java

solr/core/src/java/org/apache/solr/handler/component/QueryComponent.java

solr/core/src/java/org/apache/solr/search/combine/QueryAndResponseCombiner.java

alessandrobenedetti · 2025-07-10T09:54:16Z

Hi @ercsonusharma , thanks for resurrecting this, didn't have time to dedicate to the feature in the last few months, good to see some movement!

In the next couple of weeks, I should be able to give it a go and review it!

solr/core/src/java/org/apache/solr/handler/component/CombinedQuerySearchHandler.java

solr/core/src/java/org/apache/solr/handler/component/CombinedQueryComponent.java

ercsonusharma · 2025-09-16T04:14:38Z

@dsmiley, Really appreciate your time and effort so far on the PR. When you have a moment, would you mind taking a look at the latest commit changes addressing the concerns raised previously? Thanks!

dsmiley

I was away at a conference; I'm back now. I just did a partial review. I have doubts that it makes sense to include "Way 1" if, I imagine, it increases the complexity / documentation matters and more fundamentally... why would someone choose it.

dsmiley · 2025-09-16T14:00:08Z

solr/core/src/java/org/apache/solr/handler/component/HttpShardHandler.java

+    if (req.getHttpSolrCall() != null
+        && StringUtils.isEmpty(req.getParams().get(ShardParams.SHARDS))) {
+      String scheme = req.getHttpSolrCall().getReq().getScheme();
+      String host = req.getHttpSolrCall().getReq().getServerName();
+      int port = req.getHttpSolrCall().getReq().getServerPort();
+      String context = req.getHttpSolrCall().getReq().getContextPath();
+      String core = req.getCore().getName();
+      String localShardUrl =
+          String.format(Locale.ROOT, "%s://%s:%d%s/%s", scheme, host, port, context, core);
+      solrParams.set(ShardParams.SHARDS, localShardUrl);
+      req.setParams(solrParams);
+      return;
+    }


This part looks suspicious to me; so shortCircuit=false isn't enough? Did you construct this based on seeing similar code elsewhere (where?) to create a shards URL?

No, shortCircuit=false is not enough as ShardHandler also needs the shards parameter which comes directly from SolrParams. While, making shortCircuit=true makes the rb.isDistrib=false and force the method to not go through the shardHandler requests, rather stick to node local indexes through SearchComponent.process method.
I couldn't find this code anywhere but created myself.

Ah. I see so it needs to happen somewhere, and you've put it here. It feels out of place in this method, however. Based on what you showed me, it could be in HttpShardHandler where StandaloneReplicaSource.Builder is used.

Also, the URL core construction here seems like it should be a utility method on HttpSolrCall

solr/core/src/java/org/apache/solr/handler/component/ResponseBuilder.java

solr/core/src/test/org/apache/solr/handler/component/CombinedQueryComponentTest.java

ercsonusharma · 2025-09-16T15:37:19Z

I have doubts that it makes sense to include "Way 1" if, I imagine, it increases the complexity/documentation matters and more fundamentally... why would someone choose it.

I don't think if it introduces any additional complexity in terms of code or documentation (adding a parameter combiner.method), rather it reuses several piece of code.
IMO, If the data is independently sharded and shard-level scoring doesn't matter in overall query relevance, it may not make sense to first combine shard results based on their original scores and then apply RRF per query (as done in Way 2). In such cases, users may prefer Way 1.

dsmiley · 2025-09-16T20:20:07Z

IMO, If the data is independently sharded and shard-level scoring doesn't matter in overall query relevance, it may not make sense to first combine shard results based on their original scores and then apply RRF per query (as done in Way 2). In such cases, users may prefer Way 1.

I disagree. Only having per-shard RRF quickly devolves to shard interleaving as the shard count increases, since at the coordination/aggregation, there's no global overall ranking measure left anymore. The results from each shard are ultimately treated as equivalent across the shards. Consequently, if say the real RRF best result pointed clearly to one document (best score of both sub-queries, lets say), then in the per-shard RRF it'd merely be arbitrarily somewhere in the top-20 if say there are 20 shards. Nobody would want that.

ercsonusharma · 2025-09-17T07:39:15Z

okay @dsmiley . So I have kept only the Way 2 for now, removing Way 1 completely.

dsmiley

This PR has changed so much; I'll need to come at this afresh (not just looking at deltas from previous review). But first... can you please look at Christine's POC that leverages SearchComponent phases (as I had hinted in JIRA may be possible) #3648

ercsonusharma · 2025-09-27T07:46:31Z

@dsmiley I had a chance to take a look at Christine's POC changes and have updated my findings there.

I'll need to come at this afresh (not just looking at deltas from previous review)

Just checking in—have you had a chance to take a look at this yet?

solr/core/src/test/org/apache/solr/handler/component/DistributedCombinedQueryComponentTest.java

dsmiley · 2025-09-28T05:23:52Z

solr/core/src/test/org/apache/solr/handler/component/DistributedCombinedQueryComponentTest.java

+   * @throws Exception the exception
+   */
+  @Test
+  public void testMultipleQueryWithSort() throws Exception {


This test's existence surprises me but I'm reminded you are thinking of this feature generically, not assuming RRF. I suppose if we're sorting by a field then the underlying implementation would ideally be merely a BooleanQuery with two SHOULD clauses. Would a user bother with this plugin for such a case when they can do that trivially?

Sorting can also be applied to the results after processing RRF; otherwise, there is no built-in support for joining two queries. Sorting should be supported in case of combined query to maintain consistency with the query structure. The final RRF score would act as a tie breaker.

Wouldn't a boolean OR of both subqueries without CombinedQueryComponent count as "built in support for joining two queries"? "Consistency of the query structure".... huh?

"Consistency of the query structure"

I meant user creating the query for a use case. They don't have to use two query types - Boolean specifically for sorting and Combined for others.

solr/core/src/test/org/apache/solr/handler/component/DistributedCombinedQueryComponentTest.java

ercsonusharma · 2025-10-14T16:57:49Z

@dsmiley - Just checking if you have any concerns apart from a few mentioned above, which I have resolved recently. Not sure if you had a chance to review it completely yet. Would you be able to advise on the best path forward?

dsmiley · 2025-10-15T14:24:24Z

Sorry; this PR deserves more attention but I've been prioritizing my limited time to Solr 10. I'll return to this as soon as I can... perhaps tonight. I said that to myself yesterday so it's at least at the top of my discretionary list.

solr/core/src/java/org/apache/solr/handler/component/HttpShardHandler.java

solr/core/src/java/org/apache/solr/handler/component/SearchComponent.java

dsmiley · 2025-10-16T03:18:40Z

solr/core/src/java/org/apache/solr/handler/component/CombinedQueryComponent.java

+   */
+  @Override
+  @SuppressWarnings("unchecked")
+  public void process(ResponseBuilder rb) throws IOException {


As this component forces distributed mode, why would process() be called?

With reference, In the case of distributed mode, an HTTP request is made with rb.distrib=false through ShardHandlerRequest in one of the phases. The process method would be called for that particular shard query request.

For an isShard=true request then. Okay; but then why wouldn't the logic just pass-through as normal? It's not clear why CombinedQueryComponent has any logic to accomplish at this phase. "Way 2" is only at aggregation (disbtrib=true), in my head anyway.

Sorry, took longer to reply.
The forced distributed would anyway enable the shard call (isShard=true).

then why wouldn't the logic just pass-through as normal

The process() method is directly communicating with the Searcher as we need to process each query at the shard searcher level. If you would look at the method override, it is also creating the combined docSet across queries other than few other metadata, required for merging the docs finally across the shard at the coordinator level.

However, this Searcher call per query can be further parallelised as added in comment.
@dsmiley

solr/core/src/java/org/apache/solr/handler/component/CombinedQueryComponent.java

dsmiley · 2025-10-16T03:48:52Z

solr/core/src/java/org/apache/solr/handler/component/CombinedQueryComponent.java

+  protected Map<Object, ShardDoc> createShardResult(
+      ResponseBuilder rb,
+      Map<String, List<ShardDoc>> shardDocMap,
+      SolrDocumentList responseDocs,


it's unfortunate to have a method that both returns something and also manipulates an argument. At least you documented it.

ercsonusharma · 2025-11-01T14:17:15Z

@dsmiley Was I able to address your concern through above changes and responses? Please let me know if there is more.

dsmiley

I think my fundamental concerns are addressed. I left some comments. I'd prefer that the modifications, especially relating to forceDistrib, be in a separate PR and having a basic test for forceDistrib in particular. Like just test with a dummy TestForceDistribComponent if process() is called, that distrib=false is set. Maybe it could be added to an existing distribution test in standalone and another in a distrib SolrCloud.

solr/core/src/java/org/apache/solr/handler/component/combine/package-info.java

solr/core/src/test/org/apache/solr/handler/component/CombinedQuerySolrCloudTest.java

solr/core/src/test/org/apache/solr/handler/component/CombinedQueryComponentTest.java

solr/core/src/test/org/apache/solr/handler/component/DistributedCombinedQueryComponentTest.java

solr/core/src/test/org/apache/solr/handler/component/CombinedQuerySolrCloudTest.java

dsmiley · 2025-11-04T04:34:15Z

I'll handle the forceDistrib matter; it was my idea after all so I'll see to creating a test.

…a/solr into feat_combined_query

ercsonusharma · 2025-11-04T07:58:52Z

I think my fundamental concerns are addressed. I left some comments.

Thank you, @dsmiley for the extensive review. I have addressed those comments as well.
I can add a basic test for forceDistrib for now if you wish and all other modifications and improvements can be carried out in a separate PR.

UPDATE: @dsmiley - Have added the test cases for your convenience. Kindly have a look.

Sonu Sharma added 4 commits July 4, 2025 14:24

Combined Query Feature for Multi Query Execution

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Tests: Combined Query Feature for Multi Query Execution

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Tests: Combined Query Feature for Multi Query Execution

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Tests: Combined Query Feature for Multi Query Execution

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Tests: Fix errors

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SOLR-17319: CompoundQueryComponent scribbles continued with CompoundQueryComponentTest #3648

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SOLR-17319 : Combined Query Feature for Multi Query Execution #3418

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Description

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Tests

Checklist

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