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67f6da6466
In one of the longevity tests, we observed 1.3s reactor stall which came from repair_meta::get_full_row_hashes_source_op. It traced back to a call to std::unordered_set::insert() which triggered big memory allocation and reclaim. I measured std::unordered_set, absl::flat_hash_set, absl::node_hash_set and absl::btree_set. The absl::btree_set was the only one that seastar oversized allocation checker did not warn in my tests where around 300K repair hashes were inserted into the container. - unordered_set: hash_sets=295634, time=333029199 ns - flat_hash_set: hash_sets=295634, time=312484711 ns - node_hash_set: hash_sets=295634, time=346195835 ns - btree_set: hash_sets=295634, time=341379801 ns The btree_set is a bit slower than unordered_set but it does not have huge memory allocation. I do not measure real difference of total time to finish repair of the same dataset with unordered_set and btree_set. To fix, switch to absl btree_set container. Fixes #6190