SOLR-8988: Adds query option facet.distrib.mco which when set to true allows the use of facet.mincount=1 in cloud mode

solr/CHANGES.txt

@@ -113,6 +113,9 @@ New Features
 
 * SOLR-8323, SOLR-9113: Add CollectionStateWatcher API (Alan Woodward, Scott Blum)
 
+* SOLR-8988: Adds query option facet.distrib.mco which when set to true allows the use of facet.mincount=1 in cloud mode.
+  (Keith Laban, Dennis Gove)
+
 Bug Fixes
 ----------------------
 

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

@@ -563,9 +563,16 @@ public class FacetComponent extends SearchComponent {
           // set the initial limit higher to increase accuracy
           dff.initialLimit = doOverRequestMath(dff.initialLimit, dff.overrequestRatio, 
                                                dff.overrequestCount);
-          dff.initialMincount = 0; // TODO: we could change this to 1, but would
+          
-                                   // then need more refinement for small facet
+          // If option FACET_DISTRIB_MCO is turned on then we will use 1 as the initial 
-                                   // result sets?
+          // minCount (unless the user explicitly set it to something less than 1). If 
+          // option FACET_DISTRIB_MCO is turned off then we will use 0 as the initial 
+          // minCount regardless of what the user might have provided (prior to the
+          // addition of the FACET_DISTRIB_MCO option the default logic was to use 0).
+          // As described in issues SOLR-8559 and SOLR-8988 the use of 1 provides a 
+          // significant performance boost.
+          dff.initialMincount = dff.mco ? Math.min(dff.minCount, 1) : 0;
+                                   
         } else {
           // if limit==-1, then no need to artificially lower mincount to 0 if
           // it's 1
@@ -1415,6 +1422,7 @@ public class FacetComponent extends SearchComponent {
     
     public int initialLimit; // how many terms requested in first phase
     public int initialMincount; // mincount param sent to each shard
+    public boolean mco;
     public double overrequestRatio;
     public int overrequestCount;
     public boolean needRefinements;
@@ -1433,7 +1441,9 @@ public class FacetComponent extends SearchComponent {
         = params.getFieldDouble(field, FacetParams.FACET_OVERREQUEST_RATIO, 1.5);
       this.overrequestCount 
         = params.getFieldInt(field, FacetParams.FACET_OVERREQUEST_COUNT, 10);
-                             
+      
+      this.mco 
+      = params.getFieldBool(field, FacetParams.FACET_DISTRIB_MCO, false);
     }
     
     void add(int shardNum, NamedList shardCounts, int numRequested) {

solr/core/src/test/org/apache/solr/cloud/TestCloudPivotFacet.java

@@ -53,6 +53,7 @@ import static org.apache.solr.common.params.FacetParams.FACET_OVERREQUEST_RATIO;
 import static org.apache.solr.common.params.FacetParams.FACET_PIVOT;
 import static org.apache.solr.common.params.FacetParams.FACET_PIVOT_MINCOUNT;
 import static org.apache.solr.common.params.FacetParams.FACET_SORT;
+import static org.apache.solr.common.params.FacetParams.FACET_DISTRIB_MCO;
 
 /**
  * <p>
@@ -84,6 +85,8 @@ public class TestCloudPivotFacet extends AbstractFullDistribZkTestBase {
   // param used by test purely for tracing & validation
   private static String TRACE_MIN = "_test_min";
   // param used by test purely for tracing & validation
+  private static String TRACE_DISTRIB_MIN = "_test_distrib_min";
+  // param used by test purely for tracing & validation
   private static String TRACE_MISS = "_test_miss";
   // param used by test purely for tracing & validation
   private static String TRACE_SORT = "_test_sort";
@@ -190,6 +193,12 @@ public class TestCloudPivotFacet extends AbstractFullDistribZkTestBase {
         // trace param for validation
         baseP.add(TRACE_MIN, min);
       }
+      
+      if (random().nextBoolean()) {
+        pivotP.add(FACET_DISTRIB_MCO, "true");
+        // trace param for validation
+        baseP.add(TRACE_DISTRIB_MIN, "true");
+      }
 
       if (random().nextBoolean()) {
         String missing = ""+random().nextBoolean();

solr/solrj/src/java/org/apache/solr/common/params/FacetParams.java

@@ -122,6 +122,23 @@ public interface FacetParams {
   public static final String FACET_OVERREQUEST_COUNT = FACET_OVERREQUEST + ".count";
 
 
+  public static final String FACET_DISTRIB = FACET + ".distrib";
+  
+  /**
+   * If we are returning facet field counts, are sorting those facets by their count, and the minimum count to return is > 0,
+   * then allow the use of facet.mincount = 1 in cloud mode. To enable this use facet.distrib.mco=true.
+   *
+   * i.e. If the following three conditions are met in cloud mode: facet.sort=count, facet.limit > 0, facet.mincount > 0.
+   * Then use facet.mincount=1.
+   *
+   * Previously and by default facet.mincount will be explicitly set to 0 when in cloud mode for this condition.
+   * In SOLR-8599 and SOLR-8988, significant performance increase has been seen when enabling this optimization.
+   *
+   * Note: enabling this flag has no effect when the conditions above are not met. For those other cases the default behavior is sufficient.
+   */
+
+  public static final String FACET_DISTRIB_MCO = FACET_DISTRIB + ".mco";
+  
   /**
    * Comma separated list of fields to pivot
    *