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sstables: add generation_generator

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to prepare for the uuid-based generation identifier, where we
will generate uuid-based generation idenfier if corresponding
option is enabled, otherwise an integer based id. to reduce the
repeatings, generation_generator is extracted out so it can be reused.

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
This commit is contained in:
Kefu Chai
2023-04-17 18:31:53 +08:00
parent b0ef053552
commit 6e82aa42d5
1 changed files with 31 additions and 0 deletions
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31
sstables/generation_type.hh
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@@ -13,7 +13,9 @@
#include <compare>
#include <limits>
#include <iostream>
#include <type_traits>
#include <boost/range/adaptors.hpp>
#include <seastar/core/smp.hh>
#include <seastar/core/sstring.hh>
namespace sstables {
@@ -56,6 +58,35 @@ Target generations_from_values(std::initializer_list<generation_type::int_t> val
}));
}
class sstable_generation_generator {
// We still want to do our best to keep the generation numbers shard-friendly.
// Each destination shard will manage its own generation counter.
//
// operator() is called by multiple shards in parallel when performing reshard,
// so we have to use atomic<> here.
using int_t = sstables::generation_type::int_t;
int_t _last_generation;
static int_t base_generation(int_t highest_generation) {
// get the base generation so we can increment it by smp::count without
// conflicting with other shards
return highest_generation - highest_generation % seastar::smp::count + seastar::this_shard_id();
}
public:
explicit sstable_generation_generator(int64_t last_generation)
: _last_generation(base_generation(last_generation)) {}
void update_known_generation(int64_t generation) {
if (generation > _last_generation) {
_last_generation = generation;
}
}
sstables::generation_type operator()() {
// each shard has its own "namespace" so we increment the generation id
// by smp::count to avoid name confliction of sstables
_last_generation += seastar::smp::count;
return sstables::generation_from_value(_last_generation);
}
};
} //namespace sstables
namespace std {