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Posted to commits@cassandra.apache.org by "C. Scott Andreas (JIRA)" <ji...@apache.org> on 2018/11/18 18:29:03 UTC
[jira] [Updated] (CASSANDRA-6441) Explore merging memtables
directly with L1
[ https://issues.apache.org/jira/browse/CASSANDRA-6441?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
C. Scott Andreas updated CASSANDRA-6441:
----------------------------------------
Component/s: Compaction
> Explore merging memtables directly with L1
> ------------------------------------------
>
> Key: CASSANDRA-6441
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6441
> Project: Cassandra
> Issue Type: Improvement
> Components: Compaction
> Reporter: Jonathan Ellis
> Priority: Minor
> Labels: compaction
> Fix For: 4.x
>
>
> Currently, memtables flush to L0 and are then compacted with L1, so you automatically have 100% write amplification for unique cells right off the bat.
> http://dl.acm.org/citation.cfm?id=2213862 suggests splitting the memtable into pieces corresponding to the ranges of the sstables in L1 and turning the flush + compact into a single write -- that is, we'd "compact" the data in the L1 sstable with the corresponding data in the memtable.
> This would add some complexity around blocking memtable sections until the corresponding L1 piece is no longer involved in its own compaction with L2, and probably a "panic dump" to the old L0 behavior if we run low on memory. But in theory it sounds like a promising optimization.
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