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  1. Avro
  2. AVRO-2188

SpecificDatumReader Corrupts Bytes Field When Using Next(R)

    Details

    • Type: Bug
    • Status: Open
    • Priority: Minor
    • Resolution: Unresolved
    • Affects Version/s: 1.8.2
    • Fix Version/s: None
    • Component/s: java
    • Labels:
      None

      Description

      I am loading large sets of data into Avro files and cataloging them for quick access. My code for the load looks a bit like this.

      DataFileWriter<MyData> writer;
      final long offset = writer.sync();
      writer.append(data);
      

       

       

      When I am ready to read the data, that was the code that I initially used.

      SpecificDatumReader<MyDat> reader;
      reader.sync(offset);
      
      while (reader.hasNext()) {
        MyData data = reader.next();
        if (matchesId(data)) return data;
      }
      

       

       

      This worked for the majority of cases. But a few of them had a problem with the call to sync. In these cases a call to "reader.tell()" indicated that the sync was actually PAST the offset. This meant that I would never retrieve the file that I wanted.

      In order to work around this issue, I implemented a simple reversal algorithm which works roughly like this.

      SpecificDatumReader<MyDat> reader;
      reader.sync(offset);
      
      long reversal = 10;
      while (reader.tell() >= offset) {
        reader.sync(offset - reversal);
        reversal *= 2;
      }
      
      while (reader.hasNext()) {
        MyData data = reader.next();
        if (matchesId(data)) return data;
      }

       

       

      This works correctly in, what I believe, are all cases. Now I am SURE that I am doing something wrong, since this process seems like an extremely convoluted way to retrieve data. However, the issue is what happened next.

      To see if performance could be improved, I changed my last loop to this.

      MyData data;
      while (reader.hasNext()) {
        data = reader.next(data);
        if (matchesId(data)) return data;
      }

       

       

      My schema has several string fields and a contents field which is bytes. It looks something like this.

      {
        "title": "the title",
        "contents": "[base 64 file contents]"
      }
      

       

       

      Once I made the change for performance, I started seeing data returned like this.

       

      {
        "title": "the title",
        "contents": "[file contents][fragment of contents from previous file]"
      }
      

       

       

       

      I'm thinking that this is because the byte array is being reused. Any ideas on this?

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            • Assignee:
              Unassigned
              Reporter:
              dgrahn Dan Grahn
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              • Created:
                Updated: