[ 
https://issues.apache.org/jira/browse/SOLR-9269?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15387962#comment-15387962
 ] 

ASF GitHub Bot commented on SOLR-9269:
--------------------------------------

Github user dsmiley commented on a diff in the pull request:

    https://github.com/apache/lucene-solr/pull/52#discussion_r71736862
  
    --- 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 --
    
    The "static synchronized" concerns me for the methods in this class.  This 
will lock this operation for the whole JVM!  Perhaps we can modify the code in 
this class to be tolerant of concurrent invocations.  e.g. If we fail to delete 
a file and the exception is a FileNotFoundException then move on.  There is 
similar code in Lucene.


> Ability to create/delete/list snapshots for a solr core
> -------------------------------------------------------
>
>                 Key: SOLR-9269
>                 URL: https://issues.apache.org/jira/browse/SOLR-9269
>             Project: Solr
>          Issue Type: Sub-task
>          Components: SolrCloud
>            Reporter: Hrishikesh Gadre
>            Assignee: David Smiley
>         Attachments: SOLR-9269.patch
>
>
> Support snapshot create/delete/list functionality @ the Solr core level. 
> Please refer to parent JIRA for more details.



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