bbeaudreault commented on a change in pull request #3271:
URL: https://github.com/apache/hadoop/pull/3271#discussion_r695662268
##########
File path: hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml
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@@ -4440,8 +4440,29 @@
<value>3000</value>
<description>
Base time window in ms for DFSClient retries. For each retry attempt,
- this value is extended linearly (e.g. 3000 ms for first attempt and
- first retry, 6000 ms for second retry, 9000 ms for third retry, etc.).
+ this value is extended exponentially based on
dfs.client.retry.window.multiplier.
+ </description>
+</property>
+
+<property>
+ <name>dfs.client.retry.window.multiplier</name>
+ <value>1</value>
+ <description>
+ Multiplier for extending the retry time window. For each retry attempt,
+ the retry time window is extended by multiplying
dfs.client.retry.window.base
+ by this multiplier raised to the power of the current failure count. The
default
+ value of 1 means the window will expand linearly (e.g. 3000 ms for first
attempt
+ and first retry, 6000 ms for second retry, 9000 ms for third retry, etc.).
+ </description>
+</property>
+
+<property>
+ <name>dfs.client.retry.window.max</name>
+ <value>2147483647</value>
Review comment:
Thanks so much for the review @Hexiaoqiao. The reason I chose this value
was that I wanted the changes in this PR to be totally transparent to existing
users -- so the backoff should work exactly as it does today for anyone who
upgrades. I don't know how people have tuned their backoffs today, so adding a
lower max might affect their configured backoffs. The default case will be
well-bounded by the default retries of 3. That said, I agree that there's very
little utility in waiting many minutes on a backoff. What if I put this to 30s?
Was this the only concern in terms of the default action? My test case
[testDefaultRetryPolicy](https://github.com/apache/hadoop/pull/3271/files#diff-ce7234e2a352097945c5348774888466b48f9574d4764d9415559d975d380884R47)
proves that the default case remains unchanged from trunk. The default case
was determined based on the [comment in
DFSInputStream](https://github.com/apache/hadoop/pull/3271/files#diff-f6cd7fbb9a909e1679c2d77df54b0b2fe661a66c8c89fb455fde313966d51a61L1018-L1026),
the old implementation details, and my own testing of the backoff policy prior
to this change.
I also created this spreadsheet that helped me to determine how different
multiplier values might affect the backoff:
https://docs.google.com/spreadsheets/d/1I9ejqDtJ6-krSh-YBt0qHTf3JwZu5zRlrOhbzY0kJAg/edit?usp=sharing
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