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  1. Cassandra
  2. CASSANDRA-14861

sstable min/max metadata can cause data loss

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    • Bug Category:
      Correctness - Transient Incorrect Response
    • Severity:
      Critical
    • Complexity:
      Challenging
    • Discovered By:
      Fuzz Test
    • Since Version:

      Description

      There’s a bug in the way we filter sstables in the read path that can cause sstables containing relevant range tombstones to be excluded from reads. This can cause data resurrection for an individual read, and if compaction timing is right, permanent resurrection via read repair.

      We track the min and max clustering values when writing an sstable so we can avoid reading from sstables that don’t contain the clustering values we’re looking for in a given read. The min max for each clustering column are updated for each row / RT marker we write. In the case of range tombstones markers though, we only update the min max for the clustering values they contain, which is almost never the full set of clustering values. This leaves a min/max that are above/below (respectively) the real ranges covered by the range tombstone contained in the sstable.

      For instance, assume we’re writing an sstable for a table with 3 clustering values. The current min clustering is 5:6:7. We write an RT marker for a range tombstone that deletes any row with the value 4 in the first clustering value so the open marker is [4:]. This would make the new min clustering 4:6:7 when it should really be 4:. If we do a read for clustering values of 4:5 and lower, we’ll exclude this sstable and it’s range tombstone, resurrecting any data there that this tombstone would have deleted.

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            • Assignee:
              bdeggleston Blake Eggleston
              Reporter:
              bdeggleston Blake Eggleston
              Authors:
              Blake Eggleston
              Reviewers:
              Benedict Elliott Smith, Sam Tunnicliffe
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              Dates

              • Created:
                Updated:
                Resolved: