There is a bug introduced in e74c3c8 (4.6.0) which makes memtable
reader skip one a range tombstone for a certain pattern of deletions
and under certain sequence of events.
_rt_stream contains the result of deoverlapping range tombstones which
had the same position, which were sipped from all the versions. The
result of deoverlapping may produce a range tombstone which starts
later, at the same position as a more recent tombstone which has not
been sipped from the partition version yet. If we consume the old
range tombstone from _rt_stream and then refresh the iterators, the
refresh will skip over the newer tombstone.
The fix is to drop the logic which drains _rt_stream so that
_rt_stream is always merged with partition versions.
For the problem to trigger, there have to be multiple MVCC versions
(at least 2) which contain deletions of the following form:
[a, c] @ t0
[a, b) @ t1, [b, d] @ t2
c > b
The proper sequence for such versions is (assuming d > c):
[a, b) @ t1,
[b, d] @ t2
Due to the bug, the reader will produce:
[a, b) @ t1,
[b, c] @ t0
The reader also needs to be preempted right before processing [b, d] @
t2 and iterators need to get invalidated so that
lsa_partition_reader::do_refresh_state() is called and it skips over
[b, d] @ t2. Otherwise, the reader will emit [b, d] @ t2 later. If it
does emit the proper range tombstone, it's possible that it will violate
fragment order in the stream if _rt_stream accumulated remainders
(possible with 3 MVCC versions).
The problem goes away once MVCC versions merge.
Fixes#10913Fixes#10830Closes#10914
a6aef60b93