jay vyas created MAPREDUCE-5511: ----------------------------------- Summary: Multifilewc and the mapred.* API: Is the use of getPos() valid? Key: MAPREDUCE-5511 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5511 Project: Hadoop Map/Reduce Issue Type: Bug Components: examples Reporter: jay vyas Priority: Minor
The MultiFileWordCount class in the hadoop examples libraries uses a record reader which switches between files. This behaviour can cause the RawLocalFileSystem to break in a concurrent environment because of the way buffering works (in RawLocalFileSystem, switching between streams results in a temproraily "null" inner stream, and that inner stream is called by the getPos() implementation in the custom RecordReader for MultiFileWordCount). There are basically 2 ways to handle this: 1) Wrap the getPos() implementation in the object returned by open() in the RawLocalFileSystem to cache the value of getPos() everytime it is called, so that calls to getPos() can return a valid long even if underlying stream is null. OR 2) Update the RecordReader in multifilewc to not rely on the inner input stream and cache the position / return 0 if the stream cannot return a valid value. The final question here is: Is the RecordReader for MultiFileWordCount doing the right thing ? Or is it breaking the contract of getPos()... and really... what SHOULD getPos() return if the underlying stream has already been consumed? -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira