Dan Grahn created AVRO-2188:
-------------------------------

             Summary: SpecificDatumReader Corrupts Bytes Field When Using 
Next(R)
                 Key: AVRO-2188
                 URL: https://issues.apache.org/jira/browse/AVRO-2188
             Project: Avro
          Issue Type: Bug
          Components: java
    Affects Versions: 1.8.2
            Reporter: Dan Grahn


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.
{code:java}
DataFileWriter<MyData> writer;
final long offset = writer.sync();
writer.append(data);
{code}
 

 

When I am ready to read the data, that was the code that I initially used.
{code:java}
SpecificDatumReader<MyDat> reader;
reader.sync(offset);

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

 

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.
{code:java}
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;
}{code}
 

 

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

 

My schema has several string fields and a contents field which is bytes. It 
looks something like this.
{code:java}
{
  "title": "the title",
  "contents": "[base 64 file contents]"
}
{code}
 

 

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

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

 

 

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



--
This message was sent by Atlassian JIRA
(v7.6.3#76005)

Reply via email to