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https://issues.apache.org/jira/browse/CASSANDRA-19987?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jon Haddad updated CASSANDRA-19987:
-----------------------------------
Description:
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.
This is a follow up to be done after CASSANDRA-15452 since we will have an
internal buffer.
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.
> Use direct IO for compaction reads
> ----------------------------------
>
> Key: CASSANDRA-19987
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19987
> Project: Cassandra
> Issue Type: Improvement
> Components: Local/Compaction
> Reporter: Jon Haddad
> Priority: Normal
>
> 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.
> This is a follow up to be done after CASSANDRA-15452 since we will have an
> internal buffer.
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