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From gparai <...@git.apache.org>
Subject [GitHub] drill pull request #653: DRILL-4831: Running refresh table metadata concurre...
Date Wed, 16 Nov 2016 19:05:05 GMT
Github user gparai commented on a diff in the pull request:

    https://github.com/apache/drill/pull/653#discussion_r88292269
  
    --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/store/parquet/Metadata.java
---
    @@ -495,31 +499,65 @@ 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, new String(METADATA_FILENAME + "." + randomUUID));
    --- End diff --
    
    We can avoid creating the additional string. 
    Path tmpPath = new Path(path, METADATA_FILENAME + "." + randomUUID); 


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