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https://issues.apache.org/jira/browse/CASSANDRA-20692?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Ariel Weisberg updated CASSANDRA-20692:
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Bug Category: Parent values: Correctness(12982)Level 1 values:
Unrecoverable Corruption / Loss(13161)
Complexity: Low Hanging Fruit
Discovered By: Code Inspection
Severity: Critical
> Direct IO commit log does not flush data safely
> -----------------------------------------------
>
> Key: CASSANDRA-20692
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20692
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Local/Commit Log
> Reporter: Ariel Weisberg
> Priority: Urgent
> Fix For: 5.0.x, 5.x
>
>
> [~maxwellguo] spotted this a few days ago.
> The commit log is not safe as currently written with Direct IO. It writes to
> the file, but doesn't sync the metadata on flush. That means the commit log
> may claim it has flushed (and made durable) the data, but the filesystem
> journal has not been flushed so the file length could be wrong and could
> truncate the file on restart.
> Additionally Direct IO doesn't actually make data durable on disk (emit write
> barriers) it just flushes it to the cache of the disk. If the disk cache is
> volatile then it can lose metadata and data.
> It can probably be fixed pretty trivially by opening the file with {{D_SYNC}}
> because the commit log writes up to the entire segment when it flushes so
> there is no issue with needing to add buffering to avoid too many small
> writes.
> [~amit_pawar] [~jlewandowski] [~blambov]
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