[jira] [Commented] (KUDU-2017) Incorrect calculation determining performance improvement for flush

["Todd Lipcon (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KUDU-2017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16013289#comment-16013289 ] 

Todd Lipcon commented on KUDU-2017:
-----------------------------------

Credit to [~adar] and [~danburkert] for finding this

> 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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