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Matt Kapilevich commented on CASSANDRA-6269:
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Perhaps a better and more flexible way would be to add
"max_sstables_to_read_from_L0" option on a CF. Default can be Integer.MAX_VALUE
(uncapped), and for our use-case, we'd set it to zero. But in general, I think
this option can benefit a lot of folks for whom availability is more important
than consistency. It would give a way to have predictable read performance.
> Add ability to ignore L0 on CF level
> ------------------------------------
>
> Key: CASSANDRA-6269
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6269
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Matt Kapilevich
> Attachments: L0-vs-availability.png
>
>
> One of our CF's is written to only from a batch process. We use Cassandra's
> bulk-load utility to load the data. When the load happens, the number of
> tables in L0 increases, and then comes back down as they are compacted. While
> the number of tables in L0 is high, there's increased load on the node, and
> read availability suffers, since L0 is unsorted, and therefore lookups
> against L0 are inefficient.
> This all works-as-designed, and issues around L0 are known.
> I think it would be a great addition to disable reading from L0, settable on
> CF-level, as one of Leveled Compaction options. In our case, because the data
> is written by a batch process, we are fine waiting a little longer while L0
> is compacted away. However, the decrease in availability rate while this is
> happening is an issue for us.
> I would propose to add "disable_reads_from_L0" parameter to
> compaction_strategy_options, with default being false. In cases when
> availability is much more important than consistency, like ours, user can set
> it to true.
> I've attached a graph that shows the relationship between our availability
> rate and number of tables in L0.
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