I ran into problems with post processing Flume avrodata files with Pig's AvroStorage loader. The loader will only read files with a .avro extension.
There's no section in the official AVRO spec, but the general consensus seems to be to use the ".avro" extension for writing avro data files. See AVRO-153 and Cloudera on AVRO Usage
Don't see it in Flume's Jira, but I can't be the first to raise this issue either. Any thoughts?