[SOLR-18176] HttpShardHandler query throughput bottleneck from ZooKeeper

changelog/unreleased/SOLR-18176-shardhandler-bottleneck.yml

@@ -0,0 +1,7 @@
+title: Increased query throughput by removing a call to ZooKeeper for cluster state that should have been cached
+type: fixed
+authors:
+  - name: Matthew Biscocho
+links:
+  - name: SOLR-18176
+    url: https://issues.apache.org/jira/browse/SOLR-18176

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

@@ -109,12 +109,13 @@ private void withShardsParam(Builder builder, String shardsParam) {
       if (sliceOrUrl.indexOf('/') < 0) {
         // this is a logical shard
         this.slices[i] = sliceOrUrl;
-        replicas[i] =
-            findReplicas(
-                builder,
-                shardsParam,
-                clusterState,
-                clusterState.getCollection(builder.collection).getSlice(sliceOrUrl));
+        DocCollection coll = clusterState.getCollectionOrNull(builder.collection, true);
+        if (coll == null) {
+          throw new SolrException(
+              SolrException.ErrorCode.BAD_REQUEST,
+              "Could not find collection to resolve replicas: " + builder.collection);
+        }
+        replicas[i] = findReplicas(builder, shardsParam, clusterState, coll.getSlice(sliceOrUrl));
       } else {
         // this has urls
         this.replicas[i] = StrUtils.splitSmart(sliceOrUrl, "|", true);
@@ -189,7 +190,12 @@ private void addSlices(
       String collectionName,
       String shardKeys,
       boolean multiCollection) {
-    DocCollection coll = state.getCollection(collectionName);
+    DocCollection coll = state.getCollectionOrNull(collectionName, true);
+    if (coll == null) {
+      throw new SolrException(
+          SolrException.ErrorCode.BAD_REQUEST,
+          "Could not find collection to add slices: " + collectionName);
+    }
     Collection<Slice> slices = coll.getRouter().getSearchSlices(shardKeys, params, coll);
     ClientUtils.addSlices(target, collectionName, slices, multiCollection);
   }