Investigate whether the array that holds TIP references can be removed
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Key: HADOOP-3116
URL: https://issues.apache.org/jira/browse/HADOOP-3116
Project: Hadoop Core
Issue Type: Improvement
Components: mapred
Affects Versions: 0.17.0
Reporter: Devaraj Das
Fix For: 0.18.0
The array that holds the references to TIPs is required now only to serve the
clients (web UI via JSPs and JobClient APIs, that traverse the array and create
the output). The array can now be removed since HADOOP-2119 introduces some
datastructures for running/non-running TIPs and we could probably add some more
if required (e.g., for completed TIPs). That way, we will gain when we have
large jobs (many tasks) in the sense that we don't have to go through the big
array every time a client request is made. We could instead iterate over the
datastructures. Also, we should do these traversals without locking the
JobTracker to avoid cases where long traversal leads to loss of heartbeats,
etc. Some staleness at the client side (in favor of improving the JobTracker's
performance) is probably okay.
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