[GitHub] [lucene] zhaih commented on a change in pull request #762: LUCENE-10482 Allow users to create their own DirectoryTaxonomyReaders with empty taxoArrays instead of letting the taxoEpoch decide

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zhaih commented on a change in pull request #762:
URL: https://github.com/apache/lucene/pull/762#discussion_r840006141



##########
File path: lucene/facet/src/java/org/apache/lucene/facet/taxonomy/directory/DirectoryTaxonomyReader.java
##########
@@ -78,10 +78,20 @@
   private volatile TaxonomyIndexArrays taxoArrays;
 
   /**
-   * Called only from {@link #doOpenIfChanged()}. If the taxonomy has been recreated, you should
-   * pass {@code null} as the caches and parent/children arrays.
+   * Expert: Use this method to explicitly force the {@link DirectoryTaxonomyReader} to use specific
+   * parent/children arrays and caches.
+   *
+   * <p>Called from {@link #doOpenIfChanged()}. If the taxonomy has been recreated, you should pass
+   * {@code null} as the caches and parent/children arrays.
+   *
+   * @param indexReader An indexReader that is opened in the desired Directory
+   * @param taxoWriter The {@link DirectoryTaxonomyWriter} from which to obtain newly added
+   *     categories, in real-time.
+   * @param ordinalCache a FacetLabel to Integer ordinal mapping if it already exists
+   * @param categoryCache an ordinal to FacetLabel mapping if it already exists
+   * @param taxoArrays taxonomy arrays that store the parent, siblings, children information
    */
-  DirectoryTaxonomyReader(
+  public DirectoryTaxonomyReader(

Review comment:
       Do we really need to expose this constructor? This seems a bit too much if just for use cases of forcing recreating the taxoArrays? I'm worried about allowing users to pass in customized caching components from external will eventually cause some trouble.
   
   Why not utilizing `public DirectoryTaxonomyReader(Directory directory)` or `public DirectoryTaxonomyReader(DirectoryTaxonomyWriter taxoWriter)`? Or if we want we can easily add a version where you can pass in the `IndexReader`?

##########
File path: lucene/facet/src/test/org/apache/lucene/facet/taxonomy/directory/TestAlwaysRefreshDirectoryTaxonomyReader.java
##########
@@ -0,0 +1,95 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.facet.taxonomy.directory;
+
+import java.io.IOException;
+import org.apache.lucene.facet.FacetTestCase;
+import org.apache.lucene.facet.taxonomy.FacetLabel;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.util.IOUtils;
+import org.junit.Test;
+
+public class TestAlwaysRefreshDirectoryTaxonomyReader extends FacetTestCase {

Review comment:
       I think it might be just fine to put that `AlwaysRefreshDirectoryTaxonomyReader` into facet module? It is a valid use case. Then the test here won't seems that weird.

##########
File path: lucene/facet/src/test/org/apache/lucene/facet/taxonomy/directory/TestAlwaysRefreshDirectoryTaxonomyReader.java
##########
@@ -0,0 +1,95 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.facet.taxonomy.directory;
+
+import java.io.IOException;
+import org.apache.lucene.facet.FacetTestCase;
+import org.apache.lucene.facet.taxonomy.FacetLabel;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.util.IOUtils;
+import org.junit.Test;
+
+public class TestAlwaysRefreshDirectoryTaxonomyReader extends FacetTestCase {
+
+  @Test
+  /**
+   * Tests the expert constructors in {@link DirectoryTaxonomyReader} and checks the {@link
+   * DirectoryTaxonomyReader#getInternalIndexReader()} API. Also demonstrates the need for the
+   * constructor and the API.
+   *
+   * <p>It does not check whether the private taxoArrays were actually recreated or no. We are
+   * (correctly) hiding away that complexity away from the user.
+   */
+  public void testAlwaysRefreshDirectoryTaxonomyReader() throws IOException {
+    Directory dir = newDirectory();
+    DirectoryTaxonomyWriter tw = new DirectoryTaxonomyWriter(dir);
+    tw.addCategory(new FacetLabel("a"));
+    tw.commit();
+
+    DirectoryTaxonomyReader dtr1 = new AlwaysRefreshDirectoryTaxonomyReader(dir);
+    tw.addCategory(new FacetLabel("b"));
+    tw.commit();
+    DirectoryTaxonomyReader dtr2 = dtr1.doOpenIfChanged();

Review comment:
       +1 with Mike. I think we probably want to directly simulate the case where the taxonomy index are rolling back, which could be a bit complex...
   
   Another idea is we can assert that `taxoArray` is not initialized (maybe by creating a method returning `taxoArray == null`?), because for the cached init of `DTR` the `taxoArray` will be init'd when construction, but for uncached cases the `taxoArray` will remain `null` until being used.




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