Equality comparator may be much cheaper than the fully fledged
trichotomic comparator, especially if the component types are byte order
equal but not byte order comparable.
clustering_row can stores quite a lot of data internally which makes its
move constructor not exactly cheap.
If possible it is better to move mutation_fragment around as it keeps
everything externally. This also avoids some cases when clustering row
would be extracted from mutation_fragment only to be made to create
another mutation_fragment later.
cache_streamed_mutation assumed that at least one clustering range was
specified. That was wrong since the readers are allowed to query just
for a static row (e.g. counter update that modifies only static
columns).
Fixes#2604.
Message-Id: <20170725131220.17467-1-pdziepak@scylladb.com>
This streamed mutation populates cache with
the rows requested by the read. It takes whatever
it can find in the cache and fetches the remainings
from underlying source.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
[tgrabiec:
- fixed maybe_add_to_cache_and_update_continuity() leaking entries if
the key already exists in the snapshot
- fixed a problem where population race could result in a read
missing some rows, because cache_streamed_mutation was advancing
the cursor, then deferring, and then checking continuity. We
should check continuity atomically with advancing.
- fixed rows_handle.maybe_refresh() being accessed outside of update
section in read_from_underlying() (undefined behavior)
- fixed a problem in start_reading_from_underlying() where we would
use incorrect start if lower_bound ended with a range tombstone
starting before a key.
- range tombstone trimming in add_to_buffer() could create a
tombstone which has too low start bound if last_rt.end was a
prefix and had inclusive end. invert_kind(end_kind) should be used
instead of unconditional inc_start.
- range tombstone trimming incorrectly assumed it is fine to trim
the tombstone from underlying to the previous fragment's end and
emit such tombstone. That would mean the stream can't emit any
fragments which start before previous tombstone's end. Solve with
range_tombstone_stream.
- split add_to_buffer() into overloads for clustering_row, and
range_tombstone. Better than wrapping into mutation_fragment
before the call and having add_to_buffer() rediscover the
information.
- changed maybe_add_to_cache_and_update_continuity() to not set
continuity to false for existing entries, it's not necessary
- moved range tombstone trimming to range_tombstone class
- moved range tombstone slicing code to range_tombstone_list and partition_snapshot
- can_populate::can_use_cache was unused, dropped
- dropped assumption that dummy entries are only at the end
- renamed maybe_add_to_cache_and_update_continuity() to maybe_add_to_cache()
- dropped no longer needed lower_bound class
- extracted row_handle to a seaparate patch
- made the copy-from-cache loop preemptable
- split maybe_add_next_to_buffer_and_update_continuity(bool)
- dropped cache_populator
- replaced "underlying" class with use of read_context
- replaced can_populate class with a function
- simplified lsa_manager methods to avoid moves
]
