Xingxing Di created FLUME-3308:
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Summary: TailDirSource will write an empty position json file
Key: FLUME-3308
URL: https://issues.apache.org/jira/browse/FLUME-3308
Project: Flume
Issue Type: Bug
Components: Sinks+Sources
Affects Versions: 1.8.0
Environment: Flume 1.8, TailDirSource
Reporter: Xingxing Di
We found TailDirSource has a critical issue while writing position json file:
1.In the "process" method, existingInodes.clear() then existingInodes.addAll()
is not safe, in positionWriter thread will read an empty existingInodes with
no lock ( just after clear() executed and addAll() method not called yet), this
will cause an empty json string.
2.The FileWriter is not atomic, the position json file is over 5M in our
case(which is big), after we fix the above issue, we still read an empty
position json file occasionally.
If flume was restarted and read an empty position json file, flume will tail
all files from begining, which is critical!
So we make a little change :
# Add lock for existingInodes list, and in positionWriter thread we make a
copy of existingInodes everytime.
# We replace FileWriter with an AtomicFileWriter.
Later i will make PR to share this.
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