Revision 0bb555630f5e85a1471843f8dc0dabec297c1c49 authored by Siying Dong on 08 April 2019, 20:24:29 UTC, committed by Facebook Github Bot on 08 April 2019, 20:32:06 UTC
Summary: Create new function NPHash64() and GetSliceNPHash64(), which are currently implemented using murmurhash. Replace the current direct call of murmurhash() to use the new functions if the hash results are not used in on-disk format. This will make it easier to try out or switch to alternative functions in the uses where data format compatibility doesn't need to be considered. This part shouldn't have any performance impact. Also, the sharded cache hash function is changed to the new format, because it falls into this categoery. It doesn't show visible performance impact in db_bench results. CPU showed by perf is increased from about 0.2% to 0.4% in an extreme benchmark setting (4KB blocks, no-compression, everything cached in block cache). We've known that the current hash function used, our own Hash() has serious hash quality problem. It can generate a lots of conflicts with similar input. In this use case, it means extra lock contention for reads from the same file. This slight CPU regression is worthy to me to counter the potential bad performance with hot keys. And hopefully this will get further improved in the future with a better hash function. cache_test's condition is relaxed a little bit to. The new hash is slightly more skewed in this use case, but I manually checked the data and see the hash results are still in a reasonable range. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5155 Differential Revision: D14834821 Pulled By: siying fbshipit-source-id: ec9a2c0a2f8ae4b54d08b13a5c2e9cc97aa80cb5
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db_iter.h
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root directory).
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#pragma once
#include <stdint.h>
#include <string>
#include "db/db_impl.h"
#include "db/dbformat.h"
#include "db/range_del_aggregator.h"
#include "options/cf_options.h"
#include "rocksdb/db.h"
#include "rocksdb/iterator.h"
#include "util/arena.h"
#include "util/autovector.h"
namespace rocksdb {
class Arena;
class DBIter;
// Return a new iterator that converts internal keys (yielded by
// "*internal_iter") that were live at the specified "sequence" number
// into appropriate user keys.
extern Iterator* NewDBIterator(
Env* env, const ReadOptions& read_options,
const ImmutableCFOptions& cf_options,
const MutableCFOptions& mutable_cf_options,
const Comparator* user_key_comparator, InternalIterator* internal_iter,
const SequenceNumber& sequence, uint64_t max_sequential_skip_in_iterations,
ReadCallback* read_callback, DBImpl* db_impl = nullptr,
ColumnFamilyData* cfd = nullptr, bool allow_blob = false);
// A wrapper iterator which wraps DB Iterator and the arena, with which the DB
// iterator is supposed be allocated. This class is used as an entry point of
// a iterator hierarchy whose memory can be allocated inline. In that way,
// accessing the iterator tree can be more cache friendly. It is also faster
// to allocate.
class ArenaWrappedDBIter : public Iterator {
public:
virtual ~ArenaWrappedDBIter();
// Get the arena to be used to allocate memory for DBIter to be wrapped,
// as well as child iterators in it.
virtual Arena* GetArena() { return &arena_; }
virtual ReadRangeDelAggregator* GetRangeDelAggregator();
// Set the internal iterator wrapped inside the DB Iterator. Usually it is
// a merging iterator.
virtual void SetIterUnderDBIter(InternalIterator* iter);
virtual bool Valid() const override;
virtual void SeekToFirst() override;
virtual void SeekToLast() override;
virtual void Seek(const Slice& target) override;
virtual void SeekForPrev(const Slice& target) override;
virtual void Next() override;
virtual void Prev() override;
virtual Slice key() const override;
virtual Slice value() const override;
virtual Status status() const override;
virtual Status Refresh() override;
bool IsBlob() const;
virtual Status GetProperty(std::string prop_name, std::string* prop) override;
void Init(Env* env, const ReadOptions& read_options,
const ImmutableCFOptions& cf_options,
const MutableCFOptions& mutable_cf_options,
const SequenceNumber& sequence,
uint64_t max_sequential_skip_in_iterations, uint64_t version_number,
ReadCallback* read_callback, DBImpl* db_impl, ColumnFamilyData* cfd,
bool allow_blob, bool allow_refresh);
void StoreRefreshInfo(const ReadOptions& read_options, DBImpl* db_impl,
ColumnFamilyData* cfd, ReadCallback* read_callback,
bool allow_blob) {
read_options_ = read_options;
db_impl_ = db_impl;
cfd_ = cfd;
read_callback_ = read_callback;
allow_blob_ = allow_blob;
}
private:
DBIter* db_iter_;
Arena arena_;
uint64_t sv_number_;
ColumnFamilyData* cfd_ = nullptr;
DBImpl* db_impl_ = nullptr;
ReadOptions read_options_;
ReadCallback* read_callback_;
bool allow_blob_ = false;
bool allow_refresh_ = true;
};
// Generate the arena wrapped iterator class.
// `db_impl` and `cfd` are used for reneweal. If left null, renewal will not
// be supported.
extern ArenaWrappedDBIter* NewArenaWrappedDbIterator(
Env* env, const ReadOptions& read_options,
const ImmutableCFOptions& cf_options,
const MutableCFOptions& mutable_cf_options, const SequenceNumber& sequence,
uint64_t max_sequential_skip_in_iterations, uint64_t version_number,
ReadCallback* read_callback, DBImpl* db_impl = nullptr,
ColumnFamilyData* cfd = nullptr, bool allow_blob = false,
bool allow_refresh = true);
} // namespace rocksdb
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