SOLR-15732 : queries to missing collection are slow

solr/CHANGES.txt

@@ -41,6 +41,8 @@ Bug Fixes
 
 * SOLR-15676: Fix PeerSync failure due to RealTimeGetComponent returning duplicates. (Ramsey Haddad, Christine Poerschke, David Smiley)
 
+* SOLR-15732: queries to missing collection are slow (noble)
+
 Build
 ---------------------
 

solr/core/src/java/org/apache/solr/servlet/HttpSolrCall.java

@@ -441,7 +441,10 @@ protected void extractRemotePath(String collectionName, String origCorename) thr
     } else {
       if (!retry) {
         // we couldn't find a core to work with, try reloading aliases & this collection
-        cores.getZkController().getZkStateReader().aliasesManager.update();
+        if(!cores.getZkController().getZkStateReader().aliasesManager.update()) {
+          //no change. go back
+          return;
+        }
         cores.getZkController().zkStateReader.forceUpdateCollection(collectionName);
         action = RETRY;
       }

solr/solrj/src/java/org/apache/solr/common/cloud/ZkStateReader.java

@@ -2269,7 +2269,12 @@ public boolean update() throws KeeperException, InterruptedException {
       log.debug("Checking ZK for most up to date Aliases {}", ALIASES);
       // Call sync() first to ensure the subsequent read (getData) is up to date.
       zkClient.getSolrZooKeeper().sync(ALIASES, null, null);
-      Stat stat = new Stat();
+      Stat stat = zkClient.exists(ALIASES, null, true);
+      if (stat.getVersion() <= aliases.getZNodeVersion()) {
+        //we already have the latest version.
+        return false;
+      }
+      stat = new Stat();
       final byte[] data = zkClient.getData(ALIASES, null, stat, true);
       return setIfNewer(Aliases.fromJSON(data, stat.getVersion()));
     }