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From Jeff Jirsa <jji...@gmail.com>
Subject Re: TWCS decommission and cleanups
Date Wed, 15 Nov 2017 16:17:28 GMT
It does the right thing - sstables sent to other nodes maintain their min/max timestamps so
they’ll go to the right buckets

The bucket is selected using the timestamp of the newest cell in the sstable

If you run a major compaction, you would undo the same bucketing 

Cleanup works by compacting an sstable with itself and excluding any partition no longer owned
- it makes a new sstable, the original is deleted when the new one is finished


-- 
Jeff Jirsa
 

> On Nov 15, 2017, at 7:57 AM, Benjamin Heiskell <bheiskell@datto.com> wrote:
> 
> Hello all,
> 
> How does TWCS work when decommissioning a node? Does the data distribute across the other
nodes to the current time window's sstable (like read-repairs)? Or will it compact into the
sstables for the prior windows? If that's how it works, how does it decide what sstable to
compact with? E.g.., if I ran a major compaction on one node (pushing everything into a few
sstables), then decommissioned it, what would you expect to see on other nodes? Would the
data distribute across all sstables based on the row's timestamp?
> 
> I'm also a little unclear on how cleanups work. If I run a nodetool cleanup, will that
actually re-write the old, but not completely expired sstables of prior time windows? Or are
those sstables truly immutable?
> 
> I've read through the documentation (http://cassandra.apache.org/doc/latest/operating/compaction.html#time-window-compactionstrategy)
and a few other resources (http://thelastpickle.com/blog/2016/12/08/TWCS-part1.html), but
I still don't have a clear understanding of how it works.
> 
> Any clarification would be greatly appreciated. Thanks!
> Ben

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