Github user hgadre commented on a diff in the pull request:
https://github.com/apache/lucene-solr/pull/52#discussion_r71828065
--- Diff:
solr/core/src/java/org/apache/solr/core/snapshots/SolrSnapshotManager.java ---
@@ -0,0 +1,132 @@
+/*
+ * 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.solr.core.snapshots;
+
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexCommit;
+import org.apache.lucene.store.Directory;
+import
org.apache.solr.core.snapshots.SolrSnapshotMetaDataManager.SnapshotMetaData;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * This class provides functionality required to handle the data files
corresponding to Solr snapshots.
+ */
+public class SolrSnapshotManager {
+ private static final Logger log =
LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+
+ /**
+ * This method deletes index files of the {@linkplain IndexCommit} for
the specified generation number.
+ *
+ * @param dir The index directory storing the snapshot.
+ * @param gen The generation number for the {@linkplain IndexCommit}
+ * @throws IOException in case of I/O errors.
+ */
+ public static synchronized void deleteIndexFiles ( Directory dir,
Collection<SnapshotMetaData> snapshots, long gen ) throws IOException {
+ List<IndexCommit> commits = DirectoryReader.listCommits(dir);
+ Map<String, Integer> refCounts = buildRefCounts(snapshots,commits);
+ for (IndexCommit ic : commits) {
+ if (ic.getGeneration() == gen) {
+ deleteIndexFiles(dir,refCounts, ic);
+ break;
+ }
+ }
+ }
+
+ /**
+ * This method deletes all files not corresponding to a configured
snapshot in the specified index directory.
+ *
+ * @param dir The index directory to search for.
+ * @throws IOException in case of I/O errors.
+ */
+ public static synchronized void deleteNonSnapshotIndexFiles (Directory
dir, Collection<SnapshotMetaData> snapshots) throws IOException {
+ List<IndexCommit> commits = DirectoryReader.listCommits(dir);
+ Map<String, Integer> refCounts = buildRefCounts(snapshots, commits);
+ Set<Long> snapshotGenNumbers = snapshots.stream()
+
.map(SnapshotMetaData::getGenerationNumber)
+ .collect(Collectors.toSet());
+ for (IndexCommit ic : commits) {
+ if (!snapshotGenNumbers.contains(ic.getGeneration())) {
+ deleteIndexFiles(dir,refCounts, ic);
+ }
+ }
+ }
+
+ /**
+ * This method computes reference count for the index files by taking
into consideration
+ * (a) configured snapshots and (b) files sharing between two or more
{@linkplain IndexCommit} instances.
+ *
+ * @param snapshots A collection of user configured snapshots
+ * @param commits A list of {@linkplain IndexCommit} instances
+ * @return A map containing reference count for each index file referred
in one of the {@linkplain IndexCommit} instances.
+ * @throws IOException in case of I/O error.
+ */
+ public static Map<String, Integer> buildRefCounts
(Collection<SnapshotMetaData> snapshots, List<IndexCommit> commits) throws
IOException {
+ Map<String, Integer> result = new HashMap<>();
+ Map<Long, IndexCommit> commitsByGen = commits.stream().collect(
+ Collectors.toMap(IndexCommit::getGeneration, Function.identity()));
+
+ for(SnapshotMetaData md : snapshots) {
+ IndexCommit ic = commitsByGen.get(md.getGenerationNumber());
+ if (ic != null) {
+ Collection<String> fileNames = ic.getFileNames();
+ for(String fileName : fileNames) {
+ int refCount = result.getOrDefault(fileName, 0);
+ result.put(fileName, refCount+1);
+ }
+ }
+ }
+
+ return result;
+ }
+
+ /**
+ * This method deletes the index files associated with specified
<code>indexCommit</code> provided they
+ * are not referred by some other {@linkplain IndexCommit}.
+ *
+ * @param dir The index directory containing the {@linkplain
IndexCommit} to be deleted.
+ * @param refCounts A map containing reference counts for each file
associated with every {@linkplain IndexCommit}
+ * in the specified directory.
+ * @param indexCommit The {@linkplain IndexCommit} whose files need to
be deleted.
+ * @throws IOException in case of I/O errors.
+ */
+ private static synchronized void deleteIndexFiles ( Directory dir,
Map<String, Integer> refCounts, IndexCommit indexCommit ) throws IOException {
--- End diff --
Good catch! I was mainly concerned about concurrent deletion of files e.g.
due to simultaneous invocation of restore functionality. But after reviewing
ReplicationHandler code and more thinking, I don't think we need to worry about
it. Hence removed the synchronization.
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