Commit 6ccd317 introduced a bug in partition_entry::evict() where a
partition entry may be partially evicted if there are non-evictable
snapshots in it. Partially evicting some of the versions may violate
consistency of a snapshot which includes evicted versions. For one,
continuity flags are interpreted realtive to the merged view, not
within a version, so evicting from some of the versions may mark
reanges as continuous when before they were discontinuous. Also, range
tombtsones of the snapshot are taken from all versions, so we can't
partially evict some of them without marking all affected ranges as
discontinuous.
The fix is to revert back to full eviciton, and avoid moving
non-evictable snapshots to cache. When moving whole partition entry to
cache, we first create a neutral empty partition entry and then merge
the memtable entry into it just like we would if the entry already
existed.
Fixes#3215.
Tests: unit (release)
Message-Id: <1518710592-21925-2-git-send-email-tgrabiec@scylladb.com>
(cherry picked from commit b0b57b8143)
ef46067606