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https://issues.apache.org/jira/browse/CASSANDRA-1658?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12932372#action_12932372
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Peter Schuller commented on CASSANDRA-1658:
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I didn't think of that; that we can actually make the transition sequential in
terms of sstable coverage. That's great.
The only case I can think of where it might not be advantageous would be use of
the OPP on a terribly un-even workload where a gradual transition from 0-100%
in terms of the node's ring segment might imply very uneven jumps in the number
of requests going to the new cold sstable at any given moment. (Not that I'm
using this as an argument against the idea, just pointing it out.)
> support incremental sstable switching
> -------------------------------------
>
> Key: CASSANDRA-1658
> URL: https://issues.apache.org/jira/browse/CASSANDRA-1658
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Peter Schuller
> Priority: Minor
>
> I have been thinking about how to minimize the impact of compaction further
> beyond CASSANDRA-1470. 1470 deals with the impact of the compaction process
> itself in that it avoids going through the buffer cache; however, once
> compaction is complete you are still switching to new sstables which will
> imply cold reads.
> Instead of switching all at once, one could keep both the old and new
> sstables around for a bit and incrementally switch over traffic to the new
> sstables.
> A given request would go to the new or old sstable depending on e.g. the hash
> of the row key couple with the point in time relative to compaction
> completion and relative to the intended target sstable switch-over.
> In terms of end-user configuration/mnemonics, one would specify, for a given
> column family, something like "sstable transition period per gb of data" or
> similar. The "per gb of data" would refer to the size of the newly written
> sstable after a compaction. So; for a major compaction you would wait for a
> very significant period of time since the entire database just went cold. For
> a minor compaction, you would only wait for a short period of time.
> The result should be a reasonable negative impact on e.g. disk space usage,
> but hopefully a very significant impact in terms of making the sstable
> transition as smooth as possible for the node.
> I like this because it feels pretty simple, is not relying on OS specific
> features or otherwise rely on specific support from the OS other than a "well
> functioning cache mechanism", and does not imply something hugely significant
> like writing our own page cache layer. The performance w.r.t. CPU should be
> very small, but the improvement in terms of disk I/O should be very
> significant for workloads where it matters.
> The feature would be optional and per-sstable (or possibly global for the
> node).
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