Summary:
This patch reverts "Replace std::priority_queue in MergingIterator
with custom heap" (commit commit b6655a679d)
as it causes db_stress failure.
Test Plan: ./db_stress --test_batches_snapshots=1 --threads=32 --write_buffer_size=4194304 --destroy_db_initially=0 --reopen=20 --readpercent=45 --prefixpercent=5 --writepercent=35 --delpercent=5 --iterpercent=10 --db=/tmp/rocksdb_crashtest_KdCI5F --max_key=100000000 --mmap_read=0 --block_size=16384 --cache_size=1048576 --open_files=500000 --verify_checksum=1 --sync=0 --progress_reports=0 --disable_wal=0 --disable_data_sync=1 --target_file_size_base=2097152 --target_file_size_multiplier=2 --max_write_buffer_number=3 --max_background_compactions=20 --max_bytes_for_level_base=10485760 --filter_deletes=0 --memtablerep=prefix_hash --prefix_size=7 --ops_per_thread=200 --kill_random_test=97
Reviewers: igor, anthony, lovro, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D41343
main
Yueh-Hsuan Chiang
10 years ago
parent
c0b23dd5b0
commit
b7a2369fb2
@ -1,140 +0,0 @@ |
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// Copyright (c) 2013, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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#pragma once |
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#include <algorithm> |
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#include <cstdint> |
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#include <functional> |
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#include "util/autovector.h" |
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namespace rocksdb { |
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// Binary heap implementation optimized for use in multi-way merge sort.
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// Comparison to std::priority_queue:
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// - In libstdc++, std::priority_queue::pop() usually performs just over logN
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// comparisons but never fewer.
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// - std::priority_queue does not have a replace-top operation, requiring a
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// pop+push. If the replacement element is the new top, this requires
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// around 2logN comparisons.
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// - This heap's pop() uses a "schoolbook" downheap which requires up to ~2logN
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// comparisons.
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// - This heap provides a replace_top() operation which requires [1, 2logN]
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// comparisons. When the replacement element is also the new top, this
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// takes just 1 or 2 comparisons.
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//
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// The last property can yield an order-of-magnitude performance improvement
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// when merge-sorting real-world non-random data. If the merge operation is
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// likely to take chunks of elements from the same input stream, only 1
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// comparison per element is needed. In RocksDB-land, this happens when
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// compacting a database where keys are not randomly distributed across L0
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// files but nearby keys are likely to be in the same L0 file.
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//
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// The container uses the same counterintuitive ordering as
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// std::priority_queue: the comparison operator is expected to provide the
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// less-than relation, but top() will return the maximum.
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template<typename T, typename Compare = std::less<T>> |
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class BinaryHeap { |
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public: |
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BinaryHeap() { } |
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explicit BinaryHeap(Compare cmp) : cmp_(std::move(cmp)) { } |
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void push(const T& value) { |
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data_.push_back(value); |
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upheap(data_.size() - 1); |
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} |
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void push(T&& value) { |
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data_.push_back(std::move(value)); |
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upheap(data_.size() - 1); |
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} |
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const T& top() const { |
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assert(!empty()); |
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return data_.front(); |
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} |
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void replace_top(const T& value) { |
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assert(!empty()); |
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data_.front() = value; |
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downheap(get_root()); |
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} |
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void replace_top(T&& value) { |
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assert(!empty()); |
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data_.front() = std::move(value); |
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downheap(get_root()); |
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} |
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void pop() { |
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assert(!empty()); |
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data_.front() = std::move(data_.back()); |
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data_.pop_back(); |
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if (!empty()) { |
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downheap(get_root()); |
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} |
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} |
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void swap(BinaryHeap &other) { |
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std::swap(cmp_, other.cmp_); |
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data_.swap(other.data_); |
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} |
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void clear() { |
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data_.clear(); |
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} |
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bool empty() const { |
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return data_.empty(); |
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} |
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private: |
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static inline size_t get_root() { return 0; } |
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static inline size_t get_parent(size_t index) { return (index - 1) / 2; } |
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static inline size_t get_left(size_t index) { return 2 * index + 1; } |
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static inline size_t get_right(size_t index) { return 2 * index + 2; } |
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void upheap(size_t index) { |
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T v = std::move(data_[index]); |
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while (index > get_root()) { |
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const size_t parent = get_parent(index); |
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if (!cmp_(data_[parent], v)) { |
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break; |
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} |
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data_[index] = std::move(data_[parent]); |
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index = parent; |
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} |
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data_[index] = std::move(v); |
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} |
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void downheap(size_t index) { |
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T v = std::move(data_[index]); |
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while (1) { |
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const size_t left_child = get_left(index); |
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if (get_left(index) >= data_.size()) { |
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break; |
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} |
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const size_t right_child = left_child + 1; |
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assert(right_child == get_right(index)); |
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size_t picked_child = left_child; |
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if (right_child < data_.size() && |
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cmp_(data_[left_child], data_[right_child])) { |
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picked_child = right_child; |
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} |
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if (!cmp_(v, data_[picked_child])) { |
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break; |
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} |
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data_[index] = std::move(data_[picked_child]); |
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index = picked_child; |
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} |
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data_[index] = std::move(v); |
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} |
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Compare cmp_; |
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autovector<T> data_; |
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}; |
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} // namespace rocksdb
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