SOLR-13475: Null Pointer Exception when querying collection through collection alias.

solr/CHANGES.txt

@@ -93,6 +93,11 @@ New Features
 * SOLR-12304: The MoreLikeThisComponent now supports the mlt.interestingTerms parameter.  Previously this option was
   unique to the MLT handler.   (Alessandro Benedetti via David Smiley)
 
+Bug Fixes
+----------------------
+
+* SOLR-13475: Null Pointer Exception when querying collection through collection alias. (Jörn Franke, ab)
+
 Other Changes
 ----------------------
 

solr/core/src/java/org/apache/solr/cloud/api/collections/CreateAliasCmd.java

@@ -85,6 +85,9 @@ public class CreateAliasCmd extends AliasCmd {
 
   private void callCreatePlainAlias(ZkNodeProps message, String aliasName, ZkStateReader zkStateReader) {
     final List<String> canonicalCollectionList = parseCollectionsParameter(message.get("collections"));
+    if (canonicalCollectionList.isEmpty()) {
+      throw new SolrException(BAD_REQUEST, "'collections' parameter doesn't contain any collection names.");
+    }
     final String canonicalCollectionsString = StrUtils.join(canonicalCollectionList, ',');
     validateAllCollectionsExistAndNoDuplicates(canonicalCollectionList, zkStateReader);
     zkStateReader.aliasesManager
@@ -101,6 +104,7 @@ public class CreateAliasCmd extends AliasCmd {
     if (colls instanceof List) return (List<String>) colls;
     return StrUtils.splitSmart(colls.toString(), ",", true).stream()
         .map(String::trim)
+        .filter(s -> !s.isEmpty())
         .collect(Collectors.toList());
   }
 

solr/core/src/java/org/apache/solr/cloud/api/collections/CreateCollectionCmd.java

@@ -329,8 +329,10 @@ public class CreateCollectionCmd implements OverseerCollectionMessageHandler.Cmd
         }
       }
 
-      // create an alias pointing to the new collection
+      // create an alias pointing to the new collection, if different from the collectionName
-      ocmh.zkStateReader.aliasesManager.applyModificationAndExportToZk(a -> a.cloneWithCollectionAlias(alias, collectionName));
+      if (!alias.equals(collectionName)) {
+        ocmh.zkStateReader.aliasesManager.applyModificationAndExportToZk(a -> a.cloneWithCollectionAlias(alias, collectionName));
+      }
 
     } catch (SolrException ex) {
       throw ex;

solr/core/src/java/org/apache/solr/cloud/api/collections/DeleteCollectionCmd.java

@@ -25,6 +25,7 @@ import static org.apache.solr.common.params.CommonAdminParams.ASYNC;
 import static org.apache.solr.common.params.CommonParams.NAME;
 
 import java.lang.invoke.MethodHandles;
+import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
@@ -75,7 +76,7 @@ public class DeleteCollectionCmd implements OverseerCollectionMessageHandler.Cmd
       zkStateReader.aliasesManager.update(); // aliases may have been stale; get latest from ZK
     }
 
-    String aliasReference = checkAliasReference(zkStateReader, extCollection);
+    List<String> aliasReferences = checkAliasReference(zkStateReader, extCollection);
 
     Aliases aliases = zkStateReader.getAliases();
     String collection = aliases.resolveSimpleAlias(extCollection);
@@ -135,9 +136,14 @@ public class DeleteCollectionCmd implements OverseerCollectionMessageHandler.Cmd
       // wait for a while until we don't see the collection
       zkStateReader.waitForState(collection, 60, TimeUnit.SECONDS, (liveNodes, collectionState) -> collectionState == null);
 
-      // we can delete any remaining unique alias
+      // we can delete any remaining unique aliases
-      if (aliasReference != null) {
+      if (!aliasReferences.isEmpty()) {
-        ocmh.zkStateReader.aliasesManager.applyModificationAndExportToZk(a -> a.cloneWithCollectionAlias(aliasReference, null));
+        ocmh.zkStateReader.aliasesManager.applyModificationAndExportToZk(a -> {
+          for (String alias : aliasReferences) {
+            a = a.cloneWithCollectionAlias(alias, null);
+          }
+          return a;
+        });
       }
 
 //      TimeOut timeout = new TimeOut(60, TimeUnit.SECONDS, timeSource);
@@ -178,23 +184,29 @@ public class DeleteCollectionCmd implements OverseerCollectionMessageHandler.Cmd
     }
   }
 
-  // it's ok if a collection is referenced either by none or exactly by a single alias.
+  // This method returns the single collection aliases to delete, if present, or null
-  // This method returns the single alias to delete, if present, or null
+  private List<String> checkAliasReference(ZkStateReader zkStateReader, String extCollection) throws Exception {
-  private String checkAliasReference(ZkStateReader zkStateReader, String extCollection) throws Exception {
+    Aliases aliases = zkStateReader.getAliases();
-    List<String> aliases = referencedByAlias(extCollection, zkStateReader.getAliases());
+    List<String> aliasesRefs = referencedByAlias(extCollection, aliases);
-    if (aliases.size() > 1) {
+    List<String> aliasesToDelete = new ArrayList<>();
+    if (aliasesRefs.size() > 0) {
       zkStateReader.aliasesManager.update(); // aliases may have been stale; get latest from ZK
-      aliases = referencedByAlias(extCollection, zkStateReader.getAliases());
+      aliases = zkStateReader.getAliases();
-      if (aliases.size() > 1) {
+      aliasesRefs = referencedByAlias(extCollection, aliases);
-        throw new SolrException(SolrException.ErrorCode.SERVER_ERROR,
+      if (aliasesRefs.size() > 0) {
-            "Collection : " + extCollection + " is part of aliases: " + aliases + ", remove or modify the aliases before removing this collection.");
+        for (String alias : aliasesRefs) {
+          // for back-compat in 8.x we don't automatically remove other
+          // aliases that point only to this collection
+          if (!extCollection.equals(alias)) {
+            throw new SolrException(SolrException.ErrorCode.SERVER_ERROR,
+                "Collection : " + extCollection + " is part of aliases: " + aliasesRefs + ", remove or modify the aliases before removing this collection.");
+          } else {
+            aliasesToDelete.add(alias);
+          }
+        }
       }
     }
-    if (!aliases.isEmpty()) {
+    return aliasesToDelete;
-      return aliases.get(0);
-    } else {
-      return null;
-    }
   }
 
   public static List<String> referencedByAlias(String extCollection, Aliases aliases) throws IllegalArgumentException {

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

@@ -543,9 +543,19 @@ public class AliasIntegrationTest extends SolrCloudTestCase {
         .commit(cluster.getSolrClient(), "collection2");
 
     ///////////////
+    // make sure there's only one level of alias
+    CollectionAdminRequest.deleteAlias("collection1").process(cluster.getSolrClient());
     CollectionAdminRequest.createAlias("testalias1", "collection1").process(cluster.getSolrClient());
 
-    // ensure that the alias has been registered
+    // verify proper resolution on the server-side
+    ZkStateReader zkStateReader = cluster.getSolrClient().getZkStateReader();
+    zkStateReader.aliasesManager.update();
+    Aliases aliases = zkStateReader.getAliases();
+    List<String> collections = aliases.resolveAliases("testalias1");
+    assertEquals(collections.toString(), 1, collections.size());
+    assertTrue(collections.contains("collection1"));
+
+    // ensure that the alias is visible in the API
     assertEquals("collection1",
         new CollectionAdminRequest.ListAliases().process(cluster.getSolrClient()).getAliases().get("testalias1"));
 

solr/solr-ref-guide/src/collections-api.adoc

@@ -121,8 +121,8 @@ The name of the collection with which all replicas of this collection must be co
 See <<colocating-collections.adoc#colocating-collections, Colocating collections>> for more details.
 
 `alias`::
-Starting with version 8.1 when a collection is created additionally an alias (by default with the same name) is created
+Starting with version 8.1 when a collection is created additionally an alias can be created
-that points to this collection. This parameter allows changing the name of this alias, effectively combining
+that points to this collection. This parameter allows specifying the name of this alias, effectively combining
 this operation with <<createalias, CREATEALIAS>>
 
 Collections are first created in read-write mode but can be put in `readOnly`

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

@@ -248,11 +248,15 @@ public class Aliases {
     for (int i = 0; i < level1.size(); i++) {
       String level1Alias = level1.get(i);
       List<String> level2 = collectionAliasListMap.get(level1Alias);
-      if (level2 == null && uniqueResult != null) {
+      if (level2 == null) {
-        uniqueResult.add(level1Alias);
+        // will copy all level1alias-es so far on lazy init
+        if (uniqueResult != null) {
+          uniqueResult.add(level1Alias);
+        }
       } else {
         if (uniqueResult == null) { // lazy init
           uniqueResult = new LinkedHashSet<>(level1.size());
+          // add all level1Alias-es so far
           uniqueResult.addAll(level1.subList(0, i));
         }
         uniqueResult.addAll(level2);
@@ -294,6 +298,7 @@ public class Aliases {
           entry.setValue(Collections.unmodifiableList(list));
         }
       }
+      newColAliases.entrySet().removeIf(entry -> entry.getValue().isEmpty());
     } else {
       newColProperties = this.collectionAliasProperties;// no changes
       // java representation is a list, so split before adding to maintain consistency