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https://issues.apache.org/jira/browse/CASSANDRA-6245?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13805772#comment-13805772
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Jonathan Ellis commented on CASSANDRA-6245:
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Isn't "don't copy sstables over a soon-to-be-used sequence number" a pretty
straightforward extension of the "don't copy sstables over existing in-use
sequence numbers?"
> "nodetool refresh" design is unsafe
> -----------------------------------
>
> Key: CASSANDRA-6245
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6245
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: Robert Coli
> Priority: Minor
>
> CASSANDRA-2991 added a "nodetool refresh" feature by which Cassandra is able
> to discover non-live SSTables in the datadir and make them live.
> It does this by :
> 1) looking for SSTable files in the data dir
> 2) renaming SSTables it finds into the current SSTable id sequence
> This implementation is exposed to a race with a chance of silent data loss.
> 1) Node's SSTable id sequence is on sstable #2, the next table to flush will
> get "2" as its numeric part
> 2) Copy SSTable with "2" as its numeric part into data dir
> 3) nodetool flush
> 4) notice that your "2" SSTable has been silently overwritten by a
> just-flushed "2" SSTable
> 5) nodetool refresh would still succeed, but would now be a no-op
> A simple solution would be to create a subdirectory of the datadir called
> "refresh/" to serve as the location to refresh from.
> Alternately/additionally, there is probably not really a compelling reason
> for Cassandra to completely ignore existing files at write time.. a check for
> existing files at a given index and inflating the index to avoid overwriting
> them them seems trivial and inexpensive. I will gladly file a JIRA for this
> change in isolation if there is interest.
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