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Vlad and I were working on finding the root of the problems with refresh. We found that refresh was deleting existing sstable files because of a bug in a function that was supposed to return the maximum generation of a column family. The intention of this function is to get generation from last element of column_family::_sstables, which is of type std::map. However, we were incorrectly using std::map::end() to get last element, so garbage was being read instead of maximum generation. If the garbage value is lower than the minimum generation of a column family, then reshuffle_sstables() would set generation of all existing sstables to a lower value. That would confuse our mechanism used to delete sstables because sstables loaded at boot stage were touched. Solution to this problem is about using rbegin() instead of end() to get last element from column_family::_sstables. The other problem is that refresh will only load generations that are larger than or equal to X, so new sstables with lower generation will not be loaded. Solution is about creating a set with generation of live SSTables from all shards, and using this set to determine whether a generation is new or not. The last change was about providing an unused generation to reshuffle procedure by adding one to the maximum generation. That's important to prevent reshuffle from touching an existing SSTable. Tested 'refresh' under the following scenarios: 1) Existing generations: 1, 2, 3, 4. New ones: 5, 6. 2) Existing generations: 3, 4, 5, 6. New ones: 1, 2. 3) Existing generations: 1, 2, 3, 4. New ones: 7, 8. 4) No existing generation. No new generation. 5) No existing generation. New ones: 1, 2. I also had to adapt existing testcase for reshuffle procedure. Fixes #1073. Signed-off-by: Raphael Carvalho <raphaelsc@scylladb.com> Message-Id: <1c7b8b7f94163d5cd00d90247598dd7d26442e70.1458694985.git.raphaelsc@scylladb.com>