Sam Lightfoot created CASSANDRA-21094:
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Summary: Use POSIX_FADV_SEQUENTIAL for SSTable reads during
compaction and streaming
Key: CASSANDRA-21094
URL: https://issues.apache.org/jira/browse/CASSANDRA-21094
Project: Apache Cassandra
Issue Type: Improvement
Components: Local/Compaction
Reporter: Sam Lightfoot
Assignee: Sam Lightfoot
Fix For: 5.x
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.
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