Benedict Elliott Smith created CASSANDRA-15369:
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Summary: Fake row deletions and range tombstones, causing digest
mismatch and sstable growth
Key: CASSANDRA-15369
URL: https://issues.apache.org/jira/browse/CASSANDRA-15369
Project: Cassandra
Issue Type: Bug
Components: Consistency/Coordination, Local/Memtable, Local/SSTable
Reporter: Benedict Elliott Smith
As assessed in CASSANDRA-15363, we generate fake row deletions and fake
tombstone markers under various circumstances:
* If we perform a clustering key query (or select a compact column):
* Serving from a {{Memtable}}, we will generate fake row deletions
* Serving from an sstable, we will generate fake row tombstone markers
* If we perform a slice query, we will generate only fake row tombstone
markers for any range tombstone that begins or ends outside of the limit of the
requested slice
* If we perform a multi-slice or IN query, this will occur for each
slice/clustering
Unfortunately, these different behaviours can lead to very different data
stored in sstables until a full repair is run. When we read-repair, we only
send these fake deletions or range tombstones. A fake row deletion, clustering
RT and slice RT, each produces a different digest. So for each single point
lookup we can produce a digest mismatch twice, and until a full repair is run
we can encounter an unlimited number of digest mismatches across different
overlapping queries.
Relatedly, this seems a more problematic variant of our atomicity failures
caused by our monotonic reads, since RTs can have an atomic effect across (up
to) the entire partition, whereas the propagation may happen on an arbitrarily
small portion. If the RT exists on only one node, this could plausibly lead to
fairly problematic scenario if that node fails before the range can be
repaired.
At the very least, this behaviour can lead to an almost unlimited amount of
extraneous data being stored until the range is repaired and compaction happens
to overwrite the sub-range RTs and row deletions.
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