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https://issues.apache.org/jira/browse/CASSANDRA-21147?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sam Lightfoot updated CASSANDRA-21147:
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Description:
We should support the customisable disk access mode for the cursor compaction
path as done for iterative compaction in order to enable direct IO support.
The core direct code already exists and simply needs to adopt the SSTableReader
disk access mode methods.
was:
If we use direct io to read SSTables during compaction, we can avoid polluting
the page cache with data we're about to delete. As another side effect, we
also evict pages to make room for whatever we're putting in. This unnecessary
churn leads to higher CPU overhead and can cause dips in client read latency,
as we're going to be evicting pages that could be used to serve those reads.
This is most notable with STCS as the SSTables get larger, potentially evicting
the entire hot dataset out of cache, but is affected by every compaction
strategy.
This is a follow up to be done after CASSANDRA-15452 since we will have an
internal buffer.
> Direct IO support for cursor compaction
> ----------------------------------------
>
> Key: CASSANDRA-21147
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21147
> Project: Apache Cassandra
> Issue Type: Improvement
> Components: Local/Compaction
> Reporter: Sam Lightfoot
> Assignee: Sam Lightfoot
> Priority: Normal
> Fix For: 5.x
>
>
> We should support the customisable disk access mode for the cursor compaction
> path as done for iterative compaction in order to enable direct IO support.
> The core direct code already exists and simply needs to adopt the
> SSTableReader disk access mode methods.
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