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

[GitBox <gi...@apache.org>]

mikemccand commented on code in PR #762:
URL: https://github.com/apache/lucene/pull/762#discussion_r844479016


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lucene/facet/src/java/org/apache/lucene/facet/taxonomy/directory/AlwaysRefreshDirectoryTaxonomyReader.java:
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@@ -0,0 +1,66 @@
+/*
+ * 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.index.DirectoryReader;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.util.IOUtils;
+
+/**
+ * A modified DirectoryTaxonomyReader that always recreates a new {@link
+ * AlwaysRefreshDirectoryTaxonomyReader} instance when {@link
+ * AlwaysRefreshDirectoryTaxonomyReader#doOpenIfChanged()} is called. This enables us to easily go
+ * forward or backward in time by re-computing the ordinal space during each refresh.

Review Comment:
   Hmm in the previous revision was this a test-only class?
   
   I'm nervous about making this available in the `facet` jar -- this class should only be used in exceptional cases, while most (normal) cases should use the normal `DTR` that optimizes the very common "refresh forward" case.  Can we maybe make `DTR` smarter to detect when a "roll backwards / revert" situation is happening on refresh?



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