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From "Stefan Podkowinski (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (CASSANDRA-13024) Droppable Tombstone Ratio Calculation
Date Fri, 09 Dec 2016 14:51:59 GMT

     [ https://issues.apache.org/jira/browse/CASSANDRA-13024?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Stefan Podkowinski updated CASSANDRA-13024:
-------------------------------------------
    Component/s: Compaction

> Droppable Tombstone Ratio Calculation
> -------------------------------------
>
>                 Key: CASSANDRA-13024
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13024
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Compaction
>            Reporter: Stefan Podkowinski
>
> Whenever no sstables can be compacted in a standard way, we currently try to compact
sstables that would make worthwhile candidates by evaluation {{sstable.getEstimatedDroppableTombstoneRatio(gcBefore)
<= tombstoneThreshold}}. You can find out more on how this is supposed to work and the
various settings options by reading "[About Deletes and Tombstones in Cassandra|http://thelastpickle.com/blog/2016/07/27/about-deletes-and-tombstones.html#single-sstable-compaction]"
by [~arodrime]. 
> The bad news is that currently the ratio value will vary to a great degree depending
on the data model and type of deletes, as the ratio will be created based on the number of
tombstones and number of _columns_. Any kind of tombstone will be counted here, no matter
if on column or partition level, which will give you very different ratios based on the number
of columns in your table and how you delete the data. 
> Considering a 0.20 default threshold for finding sstables with enough droppable tombstones,
it only takes 3 columns in your table to never hit the threshold at all when using partition
tombstones.



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