Summary: In get operations, merge_operands is only used in few cases. Lazily initialize it can reduce average latency in some cases Test Plan: make all check Reviewers: haobo, kailiu, dhruba Reviewed By: haobo CC: igor, nkg-, leveldb Differential Revision: https://reviews.facebook.net/D14415 Conflicts: db/db_impl.cc db/memtable.cc
656 lines
24 KiB
C++
656 lines
24 KiB
C++
// 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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//
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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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//
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// The representation of a DBImpl consists of a set of Versions. The
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// newest version is called "current". Older versions may be kept
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// around to provide a consistent view to live iterators.
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//
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// Each Version keeps track of a set of Table files per level. The
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// entire set of versions is maintained in a VersionSet.
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//
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// Version,VersionSet are thread-compatible, but require external
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// synchronization on all accesses.
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#pragma once
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#include <map>
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#include <memory>
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#include <set>
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#include <vector>
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#include <deque>
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#include "db/dbformat.h"
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#include "db/version_edit.h"
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#include "port/port.h"
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#include "db/table_cache.h"
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namespace rocksdb {
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namespace log { class Writer; }
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class Compaction;
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class Iterator;
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class MemTable;
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class TableCache;
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class Version;
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class VersionSet;
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class MergeContext;
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// Return the smallest index i such that files[i]->largest >= key.
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// Return files.size() if there is no such file.
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// REQUIRES: "files" contains a sorted list of non-overlapping files.
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extern int FindFile(const InternalKeyComparator& icmp,
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const std::vector<FileMetaData*>& files,
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const Slice& key);
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// Returns true iff some file in "files" overlaps the user key range
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// [*smallest,*largest].
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// smallest==nullptr represents a key smaller than all keys in the DB.
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// largest==nullptr represents a key largest than all keys in the DB.
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// REQUIRES: If disjoint_sorted_files, files[] contains disjoint ranges
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// in sorted order.
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extern bool SomeFileOverlapsRange(
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const InternalKeyComparator& icmp,
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bool disjoint_sorted_files,
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const std::vector<FileMetaData*>& files,
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const Slice* smallest_user_key,
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const Slice* largest_user_key);
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class Version {
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public:
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// Append to *iters a sequence of iterators that will
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// yield the contents of this Version when merged together.
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// REQUIRES: This version has been saved (see VersionSet::SaveTo)
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void AddIterators(const ReadOptions&, const EnvOptions& soptions,
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std::vector<Iterator*>* iters);
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// Lookup the value for key. If found, store it in *val and
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// return OK. Else return a non-OK status. Fills *stats.
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// Uses *operands to store merge_operator operations to apply later
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// REQUIRES: lock is not held
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struct GetStats {
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FileMetaData* seek_file;
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int seek_file_level;
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};
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void Get(const ReadOptions&, const LookupKey& key, std::string* val,
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Status* status, MergeContext* merge_context,
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GetStats* stats, const Options& db_option, bool* value_found =
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nullptr);
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// Adds "stats" into the current state. Returns true if a new
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// compaction may need to be triggered, false otherwise.
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// REQUIRES: lock is held
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bool UpdateStats(const GetStats& stats);
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// Reference count management (so Versions do not disappear out from
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// under live iterators)
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void Ref();
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void Unref();
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void GetOverlappingInputs(
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int level,
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const InternalKey* begin, // nullptr means before all keys
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const InternalKey* end, // nullptr means after all keys
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std::vector<FileMetaData*>* inputs,
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int hint_index = -1, // index of overlap file
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int* file_index = nullptr); // return index of overlap file
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void GetOverlappingInputsBinarySearch(
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int level,
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const Slice& begin, // nullptr means before all keys
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const Slice& end, // nullptr means after all keys
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std::vector<FileMetaData*>* inputs,
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int hint_index, // index of overlap file
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int* file_index); // return index of overlap file
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void ExtendOverlappingInputs(
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int level,
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const Slice& begin, // nullptr means before all keys
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const Slice& end, // nullptr means after all keys
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std::vector<FileMetaData*>* inputs,
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unsigned int index); // start extending from this index
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// Returns true iff some file in the specified level overlaps
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// some part of [*smallest_user_key,*largest_user_key].
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// smallest_user_key==NULL represents a key smaller than all keys in the DB.
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// largest_user_key==NULL represents a key largest than all keys in the DB.
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bool OverlapInLevel(int level,
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const Slice* smallest_user_key,
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const Slice* largest_user_key);
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// Returns true iff the first or last file in inputs contains
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// an overlapping user key to the file "just outside" of it (i.e.
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// just after the last file, or just before the first file)
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// REQUIRES: "*inputs" is a sorted list of non-overlapping files
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bool HasOverlappingUserKey(const std::vector<FileMetaData*>* inputs,
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int level);
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// Return the level at which we should place a new memtable compaction
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// result that covers the range [smallest_user_key,largest_user_key].
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int PickLevelForMemTableOutput(const Slice& smallest_user_key,
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const Slice& largest_user_key);
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int NumFiles(int level) const { return files_[level].size(); }
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// Return a human readable string that describes this version's contents.
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std::string DebugString(bool hex = false) const;
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// Returns the version nuber of this version
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uint64_t GetVersionNumber() {
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return version_number_;
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}
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private:
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friend class Compaction;
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friend class VersionSet;
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friend class DBImpl;
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class LevelFileNumIterator;
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Iterator* NewConcatenatingIterator(const ReadOptions&,
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const EnvOptions& soptions,
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int level) const;
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bool PrefixMayMatch(const ReadOptions& options, const EnvOptions& soptions,
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const Slice& internal_prefix, Iterator* level_iter) const;
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VersionSet* vset_; // VersionSet to which this Version belongs
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Version* next_; // Next version in linked list
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Version* prev_; // Previous version in linked list
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int refs_; // Number of live refs to this version
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// List of files per level, files in each level are arranged
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// in increasing order of keys
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std::vector<FileMetaData*>* files_;
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// A list for the same set of files that are stored in files_,
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// but files in each level are now sorted based on file
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// size. The file with the largest size is at the front.
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// This vector stores the index of the file from files_.
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std::vector< std::vector<int> > files_by_size_;
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// An index into files_by_size_ that specifies the first
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// file that is not yet compacted
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std::vector<int> next_file_to_compact_by_size_;
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// Only the first few entries of files_by_size_ are sorted.
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// There is no need to sort all the files because it is likely
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// that on a running system, we need to look at only the first
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// few largest files because a new version is created every few
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// seconds/minutes (because of concurrent compactions).
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static const int number_of_files_to_sort_ = 50;
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// Next file to compact based on seek stats.
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FileMetaData* file_to_compact_;
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int file_to_compact_level_;
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// Level that should be compacted next and its compaction score.
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// Score < 1 means compaction is not strictly needed. These fields
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// are initialized by Finalize().
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// The most critical level to be compacted is listed first
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// These are used to pick the best compaction level
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std::vector<double> compaction_score_;
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std::vector<int> compaction_level_;
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double max_compaction_score_; // max score in l1 to ln-1
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int max_compaction_score_level_; // level on which max score occurs
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// The offset in the manifest file where this version is stored.
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uint64_t offset_manifest_file_;
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// A version number that uniquely represents this version. This is
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// used for debugging and logging purposes only.
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uint64_t version_number_;
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explicit Version(VersionSet* vset, uint64_t version_number = 0);
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~Version();
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// re-initializes the index that is used to offset into files_by_size_
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// to find the next compaction candidate file.
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void ResetNextCompactionIndex(int level) {
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next_file_to_compact_by_size_[level] = 0;
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}
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// No copying allowed
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Version(const Version&);
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void operator=(const Version&);
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};
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class VersionSet {
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public:
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VersionSet(const std::string& dbname,
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const Options* options,
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const EnvOptions& storage_options,
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TableCache* table_cache,
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const InternalKeyComparator*);
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~VersionSet();
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// Apply *edit to the current version to form a new descriptor that
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// is both saved to persistent state and installed as the new
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// current version. Will release *mu while actually writing to the file.
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// REQUIRES: *mu is held on entry.
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// REQUIRES: no other thread concurrently calls LogAndApply()
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Status LogAndApply(VersionEdit* edit, port::Mutex* mu,
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bool new_descriptor_log = false);
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// Recover the last saved descriptor from persistent storage.
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Status Recover();
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// Try to reduce the number of levels. This call is valid when
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// only one level from the new max level to the old
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// max level containing files.
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// For example, a db currently has 7 levels [0-6], and a call to
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// to reduce to 5 [0-4] can only be executed when only one level
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// among [4-6] contains files.
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Status ReduceNumberOfLevels(int new_levels, port::Mutex* mu);
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// Return the current version.
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Version* current() const { return current_; }
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// Return the current manifest file number
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uint64_t ManifestFileNumber() const { return manifest_file_number_; }
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// Allocate and return a new file number
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uint64_t NewFileNumber() { return next_file_number_++; }
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// Arrange to reuse "file_number" unless a newer file number has
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// already been allocated.
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// REQUIRES: "file_number" was returned by a call to NewFileNumber().
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void ReuseFileNumber(uint64_t file_number) {
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if (next_file_number_ == file_number + 1) {
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next_file_number_ = file_number;
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}
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}
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// Return the number of Table files at the specified level.
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int NumLevelFiles(int level) const;
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// Return the combined file size of all files at the specified level.
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int64_t NumLevelBytes(int level) const;
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// Return the last sequence number.
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uint64_t LastSequence() const { return last_sequence_; }
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// Set the last sequence number to s.
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void SetLastSequence(uint64_t s) {
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assert(s >= last_sequence_);
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last_sequence_ = s;
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}
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// Mark the specified file number as used.
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void MarkFileNumberUsed(uint64_t number);
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// Return the current log file number.
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uint64_t LogNumber() const { return log_number_; }
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// Return the log file number for the log file that is currently
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// being compacted, or zero if there is no such log file.
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uint64_t PrevLogNumber() const { return prev_log_number_; }
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int NumberLevels() const { return num_levels_; }
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// Pick level and inputs for a new compaction.
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// Returns nullptr if there is no compaction to be done.
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// Otherwise returns a pointer to a heap-allocated object that
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// describes the compaction. Caller should delete the result.
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Compaction* PickCompaction();
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// Return a compaction object for compacting the range [begin,end] in
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// the specified level. Returns nullptr if there is nothing in that
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// level that overlaps the specified range. Caller should delete
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// the result.
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Compaction* CompactRange(
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int level,
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const InternalKey* begin,
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const InternalKey* end);
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// Return the maximum overlapping data (in bytes) at next level for any
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// file at a level >= 1.
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int64_t MaxNextLevelOverlappingBytes();
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// Create an iterator that reads over the compaction inputs for "*c".
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// The caller should delete the iterator when no longer needed.
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Iterator* MakeInputIterator(Compaction* c);
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// Returns true iff some level needs a compaction because it has
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// exceeded its target size.
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bool NeedsSizeCompaction() const {
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// In universal compaction case, this check doesn't really
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// check the compaction condition, but checks num of files threshold
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// only. We are not going to miss any compaction opportunity
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// but it's likely that more compactions are scheduled but
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// ending up with nothing to do. We can improve it later.
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// TODO: improve this function to be accurate for universal
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// compactions.
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int num_levels_to_check =
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(options_->compaction_style != kCompactionStyleUniversal) ?
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NumberLevels() - 1 : 1;
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for (int i = 0; i < num_levels_to_check; i++) {
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if (current_->compaction_score_[i] >= 1) {
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return true;
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}
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}
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return false;
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}
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// Returns true iff some level needs a compaction.
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bool NeedsCompaction() const {
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return ((current_->file_to_compact_ != nullptr) ||
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NeedsSizeCompaction());
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}
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// Returns the maxmimum compaction score for levels 1 to max
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double MaxCompactionScore() const {
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return current_->max_compaction_score_;
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}
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// See field declaration
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int MaxCompactionScoreLevel() const {
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return current_->max_compaction_score_level_;
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}
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// Add all files listed in any live version to *live.
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void AddLiveFiles(std::vector<uint64_t>* live_list);
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// Add all files listed in the current version to *live.
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void AddLiveFilesCurrentVersion(std::set<uint64_t>* live);
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// Return the approximate offset in the database of the data for
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// "key" as of version "v".
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uint64_t ApproximateOffsetOf(Version* v, const InternalKey& key);
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// Return a human-readable short (single-line) summary of the number
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// of files per level. Uses *scratch as backing store.
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struct LevelSummaryStorage {
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char buffer[100];
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};
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struct FileSummaryStorage {
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char buffer[1000];
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};
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const char* LevelSummary(LevelSummaryStorage* scratch) const;
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// printf contents (for debugging)
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Status DumpManifest(Options& options, std::string& manifestFileName,
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bool verbose, bool hex = false);
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// Return a human-readable short (single-line) summary of the data size
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// of files per level. Uses *scratch as backing store.
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const char* LevelDataSizeSummary(LevelSummaryStorage* scratch) const;
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// Return a human-readable short (single-line) summary of files
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// in a specified level. Uses *scratch as backing store.
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const char* LevelFileSummary(FileSummaryStorage* scratch, int level) const;
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// Return the size of the current manifest file
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const uint64_t ManifestFileSize() { return current_->offset_manifest_file_; }
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// For the specfied level, pick a compaction.
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// Returns nullptr if there is no compaction to be done.
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// If level is 0 and there is already a compaction on that level, this
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// function will return nullptr.
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Compaction* PickCompactionBySize(int level, double score);
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// Pick files to compact in Universal mode
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Compaction* PickCompactionUniversal(int level, double score);
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// Pick Universal compaction to limit read amplification
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Compaction* PickCompactionUniversalReadAmp(int level, double score,
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unsigned int ratio, unsigned int num_files);
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// Pick Universal compaction to limit space amplification.
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Compaction* PickCompactionUniversalSizeAmp(int level, double score);
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// Free up the files that were participated in a compaction
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void ReleaseCompactionFiles(Compaction* c, Status status);
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// verify that the files that we started with for a compaction
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// still exist in the current version and in the same original level.
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// This ensures that a concurrent compaction did not erroneously
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// pick the same files to compact.
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bool VerifyCompactionFileConsistency(Compaction* c);
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// used to sort files by size
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typedef struct fsize {
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int index;
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FileMetaData* file;
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} Fsize;
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// Sort all files for this version based on their file size and
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// record results in files_by_size_. The largest files are listed first.
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void UpdateFilesBySize(Version *v);
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// Get the max file size in a given level.
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uint64_t MaxFileSizeForLevel(int level);
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double MaxBytesForLevel(int level);
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Status GetMetadataForFile(
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uint64_t number, int *filelevel, FileMetaData *metadata);
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void GetLiveFilesMetaData(
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std::vector<LiveFileMetaData> *metadata);
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void GetObsoleteFiles(std::vector<FileMetaData*>* files);
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private:
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class Builder;
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struct ManifestWriter;
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friend class Compaction;
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friend class Version;
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void Init(int num_levels);
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void Finalize(Version* v, std::vector<uint64_t>&);
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void GetRange(const std::vector<FileMetaData*>& inputs,
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InternalKey* smallest,
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InternalKey* largest);
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void GetRange2(const std::vector<FileMetaData*>& inputs1,
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const std::vector<FileMetaData*>& inputs2,
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InternalKey* smallest,
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InternalKey* largest);
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void ExpandWhileOverlapping(Compaction* c);
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void SetupOtherInputs(Compaction* c);
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// Save current contents to *log
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Status WriteSnapshot(log::Writer* log);
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void AppendVersion(Version* v);
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bool ManifestContains(const std::string& record) const;
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uint64_t ExpandedCompactionByteSizeLimit(int level);
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uint64_t MaxGrandParentOverlapBytes(int level);
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Env* const env_;
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const std::string dbname_;
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const Options* const options_;
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TableCache* const table_cache_;
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const InternalKeyComparator icmp_;
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uint64_t next_file_number_;
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uint64_t manifest_file_number_;
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uint64_t last_sequence_;
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uint64_t log_number_;
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uint64_t prev_log_number_; // 0 or backing store for memtable being compacted
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int num_levels_;
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// Opened lazily
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unique_ptr<log::Writer> descriptor_log_;
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Version dummy_versions_; // Head of circular doubly-linked list of versions.
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Version* current_; // == dummy_versions_.prev_
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// Per-level key at which the next compaction at that level should start.
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// Either an empty string, or a valid InternalKey.
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std::string* compact_pointer_;
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// Per-level target file size.
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uint64_t* max_file_size_;
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// Per-level max bytes
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uint64_t* level_max_bytes_;
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// record all the ongoing compactions for all levels
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std::vector<std::set<Compaction*> > compactions_in_progress_;
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// generates a increasing version number for every new version
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uint64_t current_version_number_;
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// Queue of writers to the manifest file
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std::deque<ManifestWriter*> manifest_writers_;
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// Store the manifest file size when it is checked.
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// Save us the cost of checking file size twice in LogAndApply
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uint64_t last_observed_manifest_size_;
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std::vector<FileMetaData*> obsolete_files_;
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// storage options for all reads and writes except compactions
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const EnvOptions& storage_options_;
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// storage options used for compactions. This is a copy of
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// storage_options_ but with readaheads set to readahead_compactions_.
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const EnvOptions storage_options_compactions_;
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// No copying allowed
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VersionSet(const VersionSet&);
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void operator=(const VersionSet&);
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// Return the total amount of data that is undergoing
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// compactions per level
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void SizeBeingCompacted(std::vector<uint64_t>&);
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// Returns true if any one of the parent files are being compacted
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bool ParentRangeInCompaction(const InternalKey* smallest,
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const InternalKey* largest, int level, int* index);
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// Returns true if any one of the specified files are being compacted
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bool FilesInCompaction(std::vector<FileMetaData*>& files);
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void LogAndApplyHelper(Builder*b, Version* v,
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VersionEdit* edit, port::Mutex* mu);
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};
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// A Compaction encapsulates information about a compaction.
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class Compaction {
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public:
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~Compaction();
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// Return the level that is being compacted. Inputs from "level"
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// will be merged.
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int level() const { return level_; }
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// Outputs will go to this level
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int output_level() const { return out_level_; }
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// Return the object that holds the edits to the descriptor done
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// by this compaction.
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VersionEdit* edit() { return edit_; }
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// "which" must be either 0 or 1
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int num_input_files(int which) const { return inputs_[which].size(); }
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// Return the ith input file at "level()+which" ("which" must be 0 or 1).
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FileMetaData* input(int which, int i) const { return inputs_[which][i]; }
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// Maximum size of files to build during this compaction.
|
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uint64_t MaxOutputFileSize() const { return max_output_file_size_; }
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// Whether compression will be enabled for compaction outputs
|
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bool enable_compression() const { return enable_compression_; }
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// Is this a trivial compaction that can be implemented by just
|
|
// moving a single input file to the next level (no merging or splitting)
|
|
bool IsTrivialMove() const;
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|
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// Add all inputs to this compaction as delete operations to *edit.
|
|
void AddInputDeletions(VersionEdit* edit);
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|
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// Returns true if the information we have available guarantees that
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// the compaction is producing data in "level+1" for which no data exists
|
|
// in levels greater than "level+1".
|
|
bool IsBaseLevelForKey(const Slice& user_key);
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|
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// Returns true iff we should stop building the current output
|
|
// before processing "internal_key".
|
|
bool ShouldStopBefore(const Slice& internal_key);
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|
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// Release the input version for the compaction, once the compaction
|
|
// is successful.
|
|
void ReleaseInputs();
|
|
|
|
void Summary(char* output, int len);
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|
|
|
// Return the score that was used to pick this compaction run.
|
|
double score() const { return score_; }
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|
|
|
// Is this compaction creating a file in the bottom most level?
|
|
bool BottomMostLevel() { return bottommost_level_; }
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|
|
|
// Does this compaction include all sst files?
|
|
bool IsFullCompaction() { return is_full_compaction_; }
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|
|
|
private:
|
|
friend class Version;
|
|
friend class VersionSet;
|
|
|
|
explicit Compaction(int level, int out_level, uint64_t target_file_size,
|
|
uint64_t max_grandparent_overlap_bytes, int number_levels,
|
|
bool seek_compaction = false, bool enable_compression = true);
|
|
|
|
int level_;
|
|
int out_level_; // levels to which output files are stored
|
|
uint64_t max_output_file_size_;
|
|
uint64_t maxGrandParentOverlapBytes_;
|
|
Version* input_version_;
|
|
VersionEdit* edit_;
|
|
int number_levels_;
|
|
|
|
bool seek_compaction_;
|
|
bool enable_compression_;
|
|
|
|
// Each compaction reads inputs from "level_" and "level_+1"
|
|
std::vector<FileMetaData*> inputs_[2]; // The two sets of inputs
|
|
|
|
// State used to check for number of of overlapping grandparent files
|
|
// (parent == level_ + 1, grandparent == level_ + 2)
|
|
std::vector<FileMetaData*> grandparents_;
|
|
size_t grandparent_index_; // Index in grandparent_starts_
|
|
bool seen_key_; // Some output key has been seen
|
|
uint64_t overlapped_bytes_; // Bytes of overlap between current output
|
|
// and grandparent files
|
|
int base_index_; // index of the file in files_[level_]
|
|
int parent_index_; // index of some file with same range in files_[level_+1]
|
|
double score_; // score that was used to pick this compaction.
|
|
|
|
// Is this compaction creating a file in the bottom most level?
|
|
bool bottommost_level_;
|
|
// Does this compaction include all sst files?
|
|
bool is_full_compaction_;
|
|
|
|
// level_ptrs_ holds indices into input_version_->levels_: our state
|
|
// is that we are positioned at one of the file ranges for each
|
|
// higher level than the ones involved in this compaction (i.e. for
|
|
// all L >= level_ + 2).
|
|
std::vector<size_t> level_ptrs_;
|
|
|
|
// mark (or clear) all files that are being compacted
|
|
void MarkFilesBeingCompacted(bool);
|
|
|
|
// Initialize whether compaction producing files at the bottommost level
|
|
void SetupBottomMostLevel(bool isManual);
|
|
|
|
// In case of compaction error, reset the nextIndex that is used
|
|
// to pick up the next file to be compacted from files_by_size_
|
|
void ResetNextCompactionIndex();
|
|
};
|
|
|
|
} // namespace rocksdb
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