Scenario:
cache = [
row(pos=2, continuous=false),
row(pos=after(2), dummy=true)
]
Scanning read starts, starts populating [-inf, before(2)] from sstables.
row(pos=2) is evicted.
cache = [
row(pos=after(2), dummy=true)
]
Scanning read finishes reading from sstables.
Refreshes cache cursor via
partition_snapshot_row_cursor::maybe_refresh(), which calls
partition_snapshot_row_cursor::advance_to() because iterators are
invalidated. This advances the cursor to
after(2). no_clustering_row_between(2, after(2)) returns true, so
advance_to() returns true, and maybe_refresh() returns true. This is
interpreted by the cache reader as "the cursor has not moved forward",
so it marks the range as complete, without emitting the row with
pos=2. Also, it marks row(pos=after(2)) as continuous, so later reads
will also miss the row.
The bug is in advance_to(), which is using
no_clustering_row_between(a, b) to determine its result, which by
definition excludes the starting key.
Discovered by row_cache_test.cc::test_concurrent_reads_and_eviction
with reduced key range in the random_mutation_generator (1024 -> 16).
Fixes#11239Closes#11240
* github.com:scylladb/scylladb:
test: mvcc: Fix illegal use of maybe_refresh()
tests: row_cache_test: Add test_eviction_of_upper_bound_of_population_range()
tests: row_cache_test: Introduce one_shot mode to throttle
row_cache: Fix missing row if upper bound of population range is evicted and has adjacent dummy
d6c2f228e7