Hadoop triggers a "soft" fd leak.
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Key: HADOOP-4346
URL: https://issues.apache.org/jira/browse/HADOOP-4346
Project: Hadoop Core
Issue Type: Bug
Components: io
Affects Versions: 0.17.0
Reporter: Raghu Angadi
Starting with Hadoop-0.17, most of the network I/O uses non-blocking NIO
channels. Normal blocking reads and writes are handled by Hadoop and use our
own cache of selectors. This cache suites well for Hadoop where I/O often
occurs on many short lived threads. Number of fds consumed is proportional to
number of threads currently blocked.
If blocking I/O is done using java.*, Sun's implementation uses internal
per-thread selectors. These selectors are closed using {{sun.misc.Cleaner}}.
Looks like this cleaning is kind of like finalizers and tied to GC. This is
pretty ill suited if we have many threads that are short lived. Until GC
happens, number of these selectors keeps growing. Each selector consumes 3 fds.
Though blocking read and write are handled by Hadoop, {{connect()}} is still
the default implementation that uses per-thread selector.
Koji helped a lot in tracking this. Some sections from 'jmap' output and other
info Koji collected led to this suspicion and will include that in the next
comment.
One solution might be to handle connect() also in Hadoop using our selectors.
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