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https://issues.apache.org/jira/browse/CASSANDRA-6696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13986688#comment-13986688
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Marcus Eriksson commented on CASSANDRA-6696:
--------------------------------------------
Pushed a semi-working sstable-per vnode version here:
https://github.com/krummas/cassandra/commits/marcuse/6696-3 (by no means
review-ready)
* flushes to vnode-separate sstables, spread out over the disks available
* keeps the sstables separate during compaction, for STCS by grouping the
compactionbuckets by overlapping sstables, and with LCS by keeping a separate
manifest for every vnode.
Still quite broken, but i think good enough to evaluate if we want to go this
way, drawback is mainly that it takes a looong time to flush to 768 sstables
instead of one (768 = num_tokens=256 and rf = 3). Doing 768 parallel
compactions is also quite heavy.
Unless anyone has a brilliant idea how to make flushing and compaction less
heavy, I think we need some sort of balance here, maybe grouping the vnodes (8
or 16 vnodes per sstable perhaps?) so that we flush a more reasonable amout of
sstables, or even just going with the per-disk approach?
> Drive replacement in JBOD can cause data to reappear.
> ------------------------------------------------------
>
> Key: CASSANDRA-6696
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6696
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: sankalp kohli
> Assignee: Marcus Eriksson
> Fix For: 3.0
>
>
> In JBOD, when someone gets a bad drive, the bad drive is replaced with a new
> empty one and repair is run.
> This can cause deleted data to come back in some cases. Also this is true for
> corrupt stables in which we delete the corrupt stable and run repair.
> Here is an example:
> Say we have 3 nodes A,B and C and RF=3 and GC grace=10days.
> row=sankalp col=sankalp is written 20 days back and successfully went to all
> three nodes.
> Then a delete/tombstone was written successfully for the same row column 15
> days back.
> Since this tombstone is more than gc grace, it got compacted in Nodes A and B
> since it got compacted with the actual data. So there is no trace of this row
> column in node A and B.
> Now in node C, say the original data is in drive1 and tombstone is in drive2.
> Compaction has not yet reclaimed the data and tombstone.
> Drive2 becomes corrupt and was replaced with new empty drive.
> Due to the replacement, the tombstone in now gone and row=sankalp col=sankalp
> has come back to life.
> Now after replacing the drive we run repair. This data will be propagated to
> all nodes.
> Note: This is still a problem even if we run repair every gc grace.
>
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