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https://issues.apache.org/jira/browse/CASSANDRA-9013?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Björn Hegerfors updated CASSANDRA-9013:
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Attachment: cassandra-2.0-CASSANDRA-9013.txt
> Add new option making DTCS unify larger time windows sooner
> -----------------------------------------------------------
>
> Key: CASSANDRA-9013
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9013
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Björn Hegerfors
> Assignee: Björn Hegerfors
> Priority: Minor
> Attachments: cassandra-2.0-CASSANDRA-9013.txt
>
>
> In my very long post on CASSANDRA-6602, I mentioned a more aggressive
> windowing strategy, which looks for opportunities to compact into larger
> SSTables sooner. The original approach was that when we have min_threshold
> windows of the same size and another one of the same size appears next to
> them, those windows (not including the newest addition) merge. This new
> approach doesn't wait for a (min_threshold+1)th one. As soon as min_threshold
> windows of one size are created, they merge at once. The only exception is
> the "incoming window", which stays outside of merging with other windows
> until it is no longer the incoming window.
> This does mean that occasionally more than min_threshold SSTables, not all of
> similar size get compacted, intentionally. For example, let's say
> min_threshold is 4, then if we have 3 windows size 16, 3 windows size 4 and
> just get a 4th size 1 window that isn't the incoming window, we immediately
> merge all of those into a size 64 window. Typically we expect one SSTable to
> be in each window with a file size corresponding to the window size in some
> unit of measure. So we merge roughly 10 SSTables in that scenario.
> These bigger compactions happen rarely, about as often as a similar thing
> happens in STCS (on occasion the number of SSTables gets very small). This
> tweak to DTCS is meant to mimic that behavior in STCS. It has been observed
> that DTCS typically has 50% to 100% more SSTables than STCS, so this is a way
> to counter that.
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