mirror of https://github.com/facebook/rocksdb.git
93 lines
3.7 KiB
C++
93 lines
3.7 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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#pragma once
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#include <algorithm>
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#include "db/version_edit.h"
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namespace ROCKSDB_NAMESPACE {
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// We boost files that are closer to TTL limit. This boosting could be
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// through FileMetaData.compensated_file_size but this compensated size
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// is widely used as something similar to file size so dramatically boost
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// the value might cause unintended consequences.
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//
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// This boosting algorithm can go very fancy, but here we use a simple
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// formula which can satisify:
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// (1) Different levels are triggered slightly differently to avoid
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// too many cascading cases
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// (2) Files in the same level get boosting more when TTL gets closer.
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//
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// Don't do any boosting before TTL has past by half. This is to make
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// sure lower write amp for most of the case. And all levels should be
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// fully boosted when total TTL compaction threshold triggers.
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// Differientiate boosting ranges of each level by 1/2. This will make
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// range for each level exponentially increasing. We could do it by
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// having them to be equal, or go even fancier. We can adjust it after
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// we observe the behavior in production.
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// The threshold starting boosting:
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// +------------------------------------------------------------------ +
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// ^ ^ ^ ^ ^ ^
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// Age 0 ... | | second last level thresold
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// | |
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// | third last level
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// |
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// forth last level
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//
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// We arbitrarily set with 0 when a file is aged boost_age_start and
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// grow linearly. The ratio is arbitrarily set so that when the next level
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// starts to boost, the previous level's boosting amount is 16.
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class FileTtlBooster {
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public:
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FileTtlBooster(uint64_t current_time, uint64_t ttl, int num_non_empty_levels,
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int level)
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: current_time_(current_time) {
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if (ttl == 0 || level == 0 || level >= num_non_empty_levels - 1) {
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enabled_ = false;
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boost_age_start_ = 0;
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boost_step_ = 1;
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} else {
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enabled_ = true;
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uint64_t all_boost_start_age = ttl / 2;
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uint64_t all_boost_age_range = (ttl / 32) * 31 - all_boost_start_age;
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uint64_t boost_age_range =
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all_boost_age_range >> (num_non_empty_levels - level - 1);
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boost_age_start_ = all_boost_start_age + boost_age_range;
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const uint64_t kBoostRatio = 16;
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// prevent 0 value to avoid divide 0 error.
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boost_step_ = std::max(boost_age_range / kBoostRatio, uint64_t{1});
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}
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}
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uint64_t GetBoostScore(FileMetaData* f) {
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if (!enabled_) {
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return 1;
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}
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uint64_t oldest_ancester_time = f->TryGetOldestAncesterTime();
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if (oldest_ancester_time >= current_time_) {
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return 1;
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}
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uint64_t age = current_time_ - oldest_ancester_time;
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if (age > boost_age_start_) {
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// Use integer just for convenience.
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// We could make all file_to_order double if we want.
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// Technically this can overflow if users override timing and
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// give a very high current time. Ignore the case for simplicity.
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// Boosting is addition to current value, so +1. This will effectively
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// make boosting to kick in after the first boost_step_ is reached.
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return (age - boost_age_start_) / boost_step_ + 1;
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}
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return 1;
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}
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private:
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bool enabled_;
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uint64_t current_time_;
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uint64_t boost_age_start_;
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uint64_t boost_step_;
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};
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} // namespace ROCKSDB_NAMESPACE
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