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From amansinha100 <...@git.apache.org>
Subject [GitHub] drill pull request #653: DRILL-4831: Running refresh table metadata concurre...
Date Thu, 17 Nov 2016 08:20:17 GMT
Github user amansinha100 commented on a diff in the pull request:

    https://github.com/apache/drill/pull/653#discussion_r88399778
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/Metadata.java
---
    @@ -495,31 +499,75 @@ private ParquetFileMetadata_v3 getParquetFileMetadata_v3(ParquetTableMetadata_v3
        * @param p
        * @throws IOException
        */
    -  private void writeFile(ParquetTableMetadata_v3 parquetTableMetadata, Path p) throws
IOException {
    +  private void writeFile(ParquetTableMetadata_v3 parquetTableMetadata, String path) throws
IOException {
         JsonFactory jsonFactory = new JsonFactory();
         jsonFactory.configure(Feature.AUTO_CLOSE_TARGET, false);
         jsonFactory.configure(JsonParser.Feature.AUTO_CLOSE_SOURCE, false);
         ObjectMapper mapper = new ObjectMapper(jsonFactory);
         SimpleModule module = new SimpleModule();
         module.addSerializer(ColumnMetadata_v3.class, new ColumnMetadata_v3.Serializer());
         mapper.registerModule(module);
    -    FSDataOutputStream os = fs.create(p);
    +
    +    // If multiple clients are updating metadata cache file concurrently, the cache file
    +    // can get corrupted. To prevent this, write to a unique temporary file and then
do
    +    // atomic rename.
    +    UUID randomUUID =  UUID.randomUUID();
    +    Path tmpPath = new Path(path, METADATA_FILENAME + "." + randomUUID);
    +
    +    FSDataOutputStream os = fs.create(tmpPath);
         mapper.writerWithDefaultPrettyPrinter().writeValue(os, parquetTableMetadata);
         os.flush();
         os.close();
    +
    +    // Use fileContext API as FileSystem rename is deprecated.
    +    FileContext fileContext = FileContext.getFileContext(tmpPath.toUri());
    +    Path finalPath = new Path(path, METADATA_FILENAME);
    +
    +    try {
    +      fileContext.rename(tmpPath, finalPath, Options.Rename.OVERWRITE);
    +    } catch (Exception e) {
    +      logger.info("Metadata cache file rename from {} to {} failed", tmpPath.toString(),
finalPath.toString(), e);
    +      throw new IOException("metadata cache file rename failed");
    +    } finally {
    +      if (fs.exists(tmpPath)) {
    +        fs.delete(tmpPath, false);
    +      }
    +    }
       }
     
    -  private void writeFile(ParquetTableMetadataDirs parquetTableMetadataDirs, Path p) throws
IOException {
    +  private void writeFile(ParquetTableMetadataDirs parquetTableMetadataDirs, String path)
throws IOException {
         JsonFactory jsonFactory = new JsonFactory();
         jsonFactory.configure(Feature.AUTO_CLOSE_TARGET, false);
         jsonFactory.configure(JsonParser.Feature.AUTO_CLOSE_SOURCE, false);
         ObjectMapper mapper = new ObjectMapper(jsonFactory);
         SimpleModule module = new SimpleModule();
         mapper.registerModule(module);
    -    FSDataOutputStream os = fs.create(p);
    +
    +    // If multiple clients are updating metadata cache file concurrently, the cache file
    +    // can get corrupted. To prevent this, write to a unique temporary file and then
do
    +    // atomic rename.
    +    UUID randomUUID = UUID.randomUUID();
    +    Path tmpPath = new Path(path, METADATA_DIRECTORIES_FILENAME + "." + randomUUID);
    +
    +    FSDataOutputStream os = fs.create(tmpPath);
         mapper.writerWithDefaultPrettyPrinter().writeValue(os, parquetTableMetadataDirs);
         os.flush();
         os.close();
    +
    +    // Use fileContext API as FileSystem rename is deprecated.
    +    FileContext fileContext = FileContext.getFileContext(tmpPath.toUri());
    --- End diff --
    
    The creation and renaming of the temp file is common to both writeFile() methods except
for the METADATA_FILENAME vs METADATA_DIRECTORIES_FILENAME...can you create utility methods
and call from both places. 


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