Wei-Chiu Chuang created HDFS-16233:
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Summary: Do not use exception handler to implement copy-on-write
for EnumCounters
Key: HDFS-16233
URL: https://issues.apache.org/jira/browse/HDFS-16233
Project: Hadoop HDFS
Issue Type: Bug
Components: namenode
Reporter: Wei-Chiu Chuang
Attachments: Screen Shot 2021-09-22 at 1.59.59 PM.png
HDFS-14547 saves the NameNode heap space occupied by EnumCounters by
essentially implementing a copy-on-write strategy.
At beginning, all EnumCounters refers to the same ConstEnumCounters to save
heap space. When it is modified, an exception is thrown and the exception
handler converts ConstEnumCounters to EnumCounters object and updates it.
Using exception handler to perform anything more than occasional is bad for
performance.
Propose: use instanceof keyword to detect the type of object and do COW
accordingly.
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