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From "Jeff Jirsa (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12682) Silent data corruption and corruption propagation in Cassandra
Date Fri, 22 Sep 2017 05:08:00 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12682?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16175926#comment-16175926
] 

Jeff Jirsa commented on CASSANDRA-12682:
----------------------------------------

[~aganesan] - thank you for the post. [~jasobrown] and I were actually discussing the acknowledgements
in [your paper|https://www.usenix.org/system/files/conference/fast17/fast17-ganesan.pdf] today
and it's a shame your ticket somehow went unnoticed. I'd like to blame it on the fact that
it happened during a busy time of the year for everyone last year (immediately after the 2016
Cassandra Summit), but the real answer is that JIRA is high noise, and it's easy to miss tickets
- for future reference, dev @ cassandra.apache.org is a much better place for feedback.

{quote}
 Also, the read repair or anti-entropy can propagate the corrupted data to other intact replicas
when the corrupted value is lexically greater
{quote}

If the table is uncompressed and crc check chance is less than 1, yes. The default config
in modern versions is compression enabled and crc check chance set to 1, so the default install
SHOULD protect against that ON THE READ PATH.

{quote}
Why does Cassandra not use the CRC and digests to verify the integrity of data in the SStables
on read? 
{quote}

It CAN for the compressed sstables, for uncompressed sstables we don't currently keep checksums
in small enough data chunks to make it viable at high request rates (we'd have to amend the
sstable format to embed checksums for the uncompressed sstables - which we could certainly
do)

{quote}
Are the digest.crc32 and CRC.db files ever used?
{quote}

There exists a tool that allows you to check the whole-file checksum, though it's only used
on operator demand (and it's probably likely that few operators really use it in practice)



> Silent data corruption and corruption propagation in Cassandra
> --------------------------------------------------------------
>
>                 Key: CASSANDRA-12682
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12682
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Aishwarya Ganesan
>            Priority: Critical
>              Labels: Correctness
>             Fix For: 4.x
>
>
> Corruptions in Cassandra's SSTable data can be silently returned to users if SSTable
compression is disabled. 
> Cassandra maintains a digest.crc32 and CRC.db in the sstable directory but fails to detect
the corruptions to SSTable Data.db. Without this, Cassandra is vulnerable to silent corruptions
resulting from underlying problems in disks and file systems atop them. Studies support the
need for end to end integrity:
> https://research.cs.wisc.edu/wind/Publications/zfs-corruption-fast10.pdf
> http://www.cs.toronto.edu/~bianca/papers/fast08.pdf
> In a small test case where the underlying disk/FS corrupts a particular block holding
the user data, Cassandra can silently return corrupted user data on a read request. Also,
the read repair or anti-entropy can propagate the corrupted data to other intact replicas
when the corrupted value is lexically greater. This is because a corruption doesn't change
the timestamps and timestamp conflicts are resolved by choosing the data with the highest
value. (We reproduced this scenario using our testing framework)
> Why does Cassandra not use the CRC and digests to verify the integrity of data in the
SStables on read? Are the digest.crc32 and CRC.db files ever used?



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