[jira] [Updated] (CASSANDRA-9829) Dynamically adjust LCS level sizes

["C. Scott Andreas (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CASSANDRA-9829?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

C. Scott Andreas updated CASSANDRA-9829:
----------------------------------------
    Component/s: Compaction

> Dynamically adjust LCS level sizes
> ----------------------------------
>
>                 Key: CASSANDRA-9829
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9829
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Compaction
>            Reporter: Jonathan Ellis
>            Priority: Major
>              Labels: compaction, lcs, performance
>             Fix For: 4.x
>
>
> LCS works best when the top level is full.  Then 90% of reads can be served from a single sstable.  By contrast if the top level is only 10% full then 90% of reads will be served from two.  This results in worse performance as well as confused users.
> To address this, we can adjust the ideal top level size to how much data is actually in it (and set each corresponding lower level to 1/10 of the next one above).
> (This is an idea [from rocksdb|https://www.reddit.com/r/IAmA/comments/3de3cv/we_are_rocksdb_engineering_team_ask_us_anything/ct4asen].)



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