[jira] [Comment Edited] (CASSANDRA-11119) Add bytes-to-compact estimate

["Jonathan Ellis (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-11119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15131501#comment-15131501 ] 

Jonathan Ellis edited comment on CASSANDRA-11119 at 2/11/16 5:01 PM:
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We can actually get pretty accurate with STCS thanks to the bucketing we do anyway to compute next-task-to-compact.

For LCS we're probably still looking at some pretty rough estimates.


was (Author: jbellis):
We can actually get pretty accurate with STCS thanks to HyperLogLog.

For LCS we're probably still looking at some pretty rough estimates.

> Add bytes-to-compact estimate
> -----------------------------
>
>                 Key: CASSANDRA-11119
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11119
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Compaction
>            Reporter: Jonathan Ellis
>             Fix For: 3.x
>
>
> Pending tasks is essentially useless at letting operators know how far behind compaction is.  For STCS, because compaction tasks can vary in size by several orders of magnitude, so "4 more tasks" is a very wide range.  For LCS, I think the problem is that we only look at first-order work (how much larger is level X than it "should" be?) and not cascading effects, particularly in L0 (if we push this into L1, how much does that push into L2 etc?).
> I propose adding an estimate of bytes-to-compact (and deprecating estimated tasks).  



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