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31909515b3
Currently, the sstable_set in a table is copied before every change to allow accessing the unchanged version by existing sstable readers. This patch changes the sstable_set to a structure that keeps all its versions that are referenced somewhere and provides a way of getting a reference to an immutable version of the set. Each sstable in the set is associated with the versions it is alive in, and is removed when all such versions don't have references anymore. To avoid copying, the object holding all sstables in the set version is changed to a new structure, sstable_list, which was previously an alias for std::unordered_set<shared_sstable>, and which implements most of the methods of an unordered_set, but its iterator uses the actual set with all sstables from all referenced versions and iterates over those sstables that belong to the captured version. The methods that modify the sets contents give strong exception guarantee by trying to insert new sstables to its containers, and erasing them in the case of an caught exception. To release shared_sstables as soon as possible (i.e. when all references to versions that contain them die), each time a version is removed, all sstables that were referenced exclusively by this version are erased. We are able to find these sstables efficiently by storing, for each version, all sstables that were added and erased in it, and, when a version is removed, merging it with the next one. When a version that adds an sstable gets merged with a version that removes it, this sstable is erased. Fixes #2622 Signed-off-by: Wojciech Mitros wojciech.mitros@scylladb.com Closes #8111 * github.com:scylladb/scylla: sstables: add test for checking the latency of updating the sstable_set in a table sstables: move column_family_test class from test/boost to test/lib sstables: use fast copying of the sstable_set instead of rebuilding it sstables: replace the sstable_set with a versioned structure sstables: remove potential ub sstables: make sstable_set constructor less error-prone