Todd Lipcon created HDFS-4879:
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Summary: Add "blocked ArrayList" collection to avoid CMS full GCs
Key: HDFS-4879
URL: https://issues.apache.org/jira/browse/HDFS-4879
Project: Hadoop HDFS
Issue Type: Improvement
Components: namenode
Affects Versions: 2.0.4-alpha, 3.0.0
Reporter: Todd Lipcon
Assignee: Todd Lipcon
We recently saw an issue where a large deletion was issued which caused 25M
blocks to be collected during {{deleteInternal}}. Currently, the list of
collected blocks is an ArrayList, meaning that we had to allocate a contiguous
25M-entry array (~400MB). After a NN has been running for a long amount of
time, the old generation may become fragmented such that it's hard to find a
400MB contiguous chunk of heap.
In general, we should try to design the NN such that the only large objects are
long-lived and created at startup time. We can improve this particular case
(and perhaps some others) by introducing a new List implementation which is
made of a linked list of arrays, each of which is size-limited (eg to 1MB).
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