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108 lines
3.6 KiB
C++
108 lines
3.6 KiB
C++
/*
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* Copyright (C) 2020 ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include "dht/token.hh"
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namespace dht {
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inline sstring cpu_sharding_algorithm_name() {
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return "biased-token-round-robin";
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}
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std::vector<uint64_t> init_zero_based_shard_start(unsigned shards, unsigned sharding_ignore_msb_bits);
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unsigned shard_of(unsigned shard_count, unsigned sharding_ignore_msb_bits, const token& t);
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token token_for_next_shard(const std::vector<uint64_t>& shard_start, unsigned shard_count, unsigned sharding_ignore_msb_bits, const token& t, shard_id shard, unsigned spans);
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class sharder {
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protected:
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unsigned _shard_count;
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unsigned _sharding_ignore_msb_bits;
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std::vector<uint64_t> _shard_start;
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public:
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sharder(unsigned shard_count = smp::count, unsigned sharding_ignore_msb_bits = 0);
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virtual ~sharder() = default;
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/**
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* Calculates the shard that handles a particular token.
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*/
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virtual unsigned shard_of(const token& t) const;
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/**
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* Gets the first token greater than `t` that is in shard `shard`, and is a shard boundary (its first token).
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*
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* If the `spans` parameter is greater than zero, the result is the same as if the function
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* is called `spans` times, each time applied to its return value, but efficiently. This allows
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* selecting ranges that include multiple round trips around the 0..smp::count-1 shard span:
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*
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* token_for_next_shard(t, shard, spans) == token_for_next_shard(token_for_shard(t, shard, 1), spans - 1)
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*
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* On overflow, maximum_token() is returned.
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*/
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virtual token token_for_next_shard(const token& t, shard_id shard, unsigned spans = 1) const;
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/**
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* @return number of shards configured for this partitioner
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*/
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unsigned shard_count() const {
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return _shard_count;
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}
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unsigned sharding_ignore_msb() const {
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return _sharding_ignore_msb_bits;
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}
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bool operator==(const sharder& o) const {
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return _shard_count == o._shard_count && _sharding_ignore_msb_bits == o._sharding_ignore_msb_bits;
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}
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bool operator!=(const sharder& o) const {
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return !(*this == o);
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}
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};
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inline std::ostream& operator<<(std::ostream& os, const sharder& sharder) {
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os << "sharder[shard_count=" << sharder.shard_count()
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<< ", ignore_msb_bits="<< sharder.sharding_ignore_msb() << "]";
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return os;
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}
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/*
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* Finds the first token in token range (`start`, `end`] that belongs to shard shard_idx.
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*
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* If there is no token that belongs to shard shard_idx in this range,
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* `end` is returned.
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*
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* The first token means the one that appears first on the ring when going
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* from `start` to `end`.
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* 'first token' is not always the smallest.
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* For example, if in vnode (100, 10] only tokens 110 and 1 belong to
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* shard shard_idx then token 110 is the first because it appears first
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* when going from 100 to 10 on the ring.
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*/
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dht::token find_first_token_for_shard(
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const dht::sharder& sharder, dht::token start, dht::token end, size_t shard_idx);
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} //namespace dht
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