Todd Lipcon created KUDU-2017:
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Summary: Incorrect calculation determining performance improvement
for flush
Key: KUDU-2017
URL: https://issues.apache.org/jira/browse/KUDU-2017
Project: Kudu
Issue Type: Bug
Components: tablet
Affects Versions: 1.3.1
Reporter: Todd Lipcon
Assignee: Todd Lipcon
The code to calculate the MM "perf improvement score" for a flush had two bugs:
(1) we calculated {{threshold - current_usage}} instead of {{current_usage -
threshold}}, which resulted in a negative score
(2) we had an unsigned integer overflow, which resulted in the above negative
score becoming insanely large
These two wrongs "made a right" in which we'd still trigger flushes at the
flush threshold, which is why this went unnoticed for quite some time. However,
the flushing behavior is more aggressive than originally intended, and we would
lose the correct prioritization of flushing tablets that are farther above the
threshold.
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