diff options
Diffstat (limited to 'src/leveldb/db/version_set.h')
-rw-r--r-- | src/leveldb/db/version_set.h | 393 |
1 files changed, 393 insertions, 0 deletions
diff --git a/src/leveldb/db/version_set.h b/src/leveldb/db/version_set.h new file mode 100644 index 0000000000..69f3d70133 --- /dev/null +++ b/src/leveldb/db/version_set.h @@ -0,0 +1,393 @@ +// 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. +// +// The representation of a DBImpl consists of a set of Versions. The +// newest version is called "current". Older versions may be kept +// around to provide a consistent view to live iterators. +// +// Each Version keeps track of a set of Table files per level. The +// entire set of versions is maintained in a VersionSet. +// +// Version,VersionSet are thread-compatible, but require external +// synchronization on all accesses. + +#ifndef STORAGE_LEVELDB_DB_VERSION_SET_H_ +#define STORAGE_LEVELDB_DB_VERSION_SET_H_ + +#include <map> +#include <set> +#include <vector> + +#include "db/dbformat.h" +#include "db/version_edit.h" +#include "port/port.h" +#include "port/thread_annotations.h" + +namespace leveldb { + +namespace log { +class Writer; +} + +class Compaction; +class Iterator; +class MemTable; +class TableBuilder; +class TableCache; +class Version; +class VersionSet; +class WritableFile; + +// Return the smallest index i such that files[i]->largest >= key. +// Return files.size() if there is no such file. +// REQUIRES: "files" contains a sorted list of non-overlapping files. +int FindFile(const InternalKeyComparator& icmp, + const std::vector<FileMetaData*>& files, const Slice& key); + +// Returns true iff some file in "files" overlaps the user key range +// [*smallest,*largest]. +// smallest==nullptr represents a key smaller than all keys in the DB. +// largest==nullptr represents a key largest than all keys in the DB. +// REQUIRES: If disjoint_sorted_files, files[] contains disjoint ranges +// in sorted order. +bool SomeFileOverlapsRange(const InternalKeyComparator& icmp, + bool disjoint_sorted_files, + const std::vector<FileMetaData*>& files, + const Slice* smallest_user_key, + const Slice* largest_user_key); + +class Version { + public: + // Lookup the value for key. If found, store it in *val and + // return OK. Else return a non-OK status. Fills *stats. + // REQUIRES: lock is not held + struct GetStats { + FileMetaData* seek_file; + int seek_file_level; + }; + + // Append to *iters a sequence of iterators that will + // yield the contents of this Version when merged together. + // REQUIRES: This version has been saved (see VersionSet::SaveTo) + void AddIterators(const ReadOptions&, std::vector<Iterator*>* iters); + + Status Get(const ReadOptions&, const LookupKey& key, std::string* val, + GetStats* stats); + + // Adds "stats" into the current state. Returns true if a new + // compaction may need to be triggered, false otherwise. + // REQUIRES: lock is held + bool UpdateStats(const GetStats& stats); + + // Record a sample of bytes read at the specified internal key. + // Samples are taken approximately once every config::kReadBytesPeriod + // bytes. Returns true if a new compaction may need to be triggered. + // REQUIRES: lock is held + bool RecordReadSample(Slice key); + + // Reference count management (so Versions do not disappear out from + // under live iterators) + void Ref(); + void Unref(); + + void GetOverlappingInputs( + int level, + const InternalKey* begin, // nullptr means before all keys + const InternalKey* end, // nullptr means after all keys + std::vector<FileMetaData*>* inputs); + + // Returns true iff some file in the specified level overlaps + // some part of [*smallest_user_key,*largest_user_key]. + // smallest_user_key==nullptr represents a key smaller than all the DB's keys. + // largest_user_key==nullptr represents a key largest than all the DB's keys. + bool OverlapInLevel(int level, const Slice* smallest_user_key, + const Slice* largest_user_key); + + // Return the level at which we should place a new memtable compaction + // result that covers the range [smallest_user_key,largest_user_key]. + int PickLevelForMemTableOutput(const Slice& smallest_user_key, + const Slice& largest_user_key); + + int NumFiles(int level) const { return files_[level].size(); } + + // Return a human readable string that describes this version's contents. + std::string DebugString() const; + + private: + friend class Compaction; + friend class VersionSet; + + class LevelFileNumIterator; + + explicit Version(VersionSet* vset) + : vset_(vset), + next_(this), + prev_(this), + refs_(0), + file_to_compact_(nullptr), + file_to_compact_level_(-1), + compaction_score_(-1), + compaction_level_(-1) {} + + Version(const Version&) = delete; + Version& operator=(const Version&) = delete; + + ~Version(); + + Iterator* NewConcatenatingIterator(const ReadOptions&, int level) const; + + // Call func(arg, level, f) for every file that overlaps user_key in + // order from newest to oldest. If an invocation of func returns + // false, makes no more calls. + // + // REQUIRES: user portion of internal_key == user_key. + void ForEachOverlapping(Slice user_key, Slice internal_key, void* arg, + bool (*func)(void*, int, FileMetaData*)); + + VersionSet* vset_; // VersionSet to which this Version belongs + Version* next_; // Next version in linked list + Version* prev_; // Previous version in linked list + int refs_; // Number of live refs to this version + + // List of files per level + std::vector<FileMetaData*> files_[config::kNumLevels]; + + // Next file to compact based on seek stats. + FileMetaData* file_to_compact_; + int file_to_compact_level_; + + // Level that should be compacted next and its compaction score. + // Score < 1 means compaction is not strictly needed. These fields + // are initialized by Finalize(). + double compaction_score_; + int compaction_level_; +}; + +class VersionSet { + public: + VersionSet(const std::string& dbname, const Options* options, + TableCache* table_cache, const InternalKeyComparator*); + VersionSet(const VersionSet&) = delete; + VersionSet& operator=(const VersionSet&) = delete; + + ~VersionSet(); + + // Apply *edit to the current version to form a new descriptor that + // is both saved to persistent state and installed as the new + // current version. Will release *mu while actually writing to the file. + // REQUIRES: *mu is held on entry. + // REQUIRES: no other thread concurrently calls LogAndApply() + Status LogAndApply(VersionEdit* edit, port::Mutex* mu) + EXCLUSIVE_LOCKS_REQUIRED(mu); + + // Recover the last saved descriptor from persistent storage. + Status Recover(bool* save_manifest); + + // Return the current version. + Version* current() const { return current_; } + + // Return the current manifest file number + uint64_t ManifestFileNumber() const { return manifest_file_number_; } + + // Allocate and return a new file number + uint64_t NewFileNumber() { return next_file_number_++; } + + // Arrange to reuse "file_number" unless a newer file number has + // already been allocated. + // REQUIRES: "file_number" was returned by a call to NewFileNumber(). + void ReuseFileNumber(uint64_t file_number) { + if (next_file_number_ == file_number + 1) { + next_file_number_ = file_number; + } + } + + // Return the number of Table files at the specified level. + int NumLevelFiles(int level) const; + + // Return the combined file size of all files at the specified level. + int64_t NumLevelBytes(int level) const; + + // Return the last sequence number. + uint64_t LastSequence() const { return last_sequence_; } + + // Set the last sequence number to s. + void SetLastSequence(uint64_t s) { + assert(s >= last_sequence_); + last_sequence_ = s; + } + + // Mark the specified file number as used. + void MarkFileNumberUsed(uint64_t number); + + // Return the current log file number. + uint64_t LogNumber() const { return log_number_; } + + // Return the log file number for the log file that is currently + // being compacted, or zero if there is no such log file. + uint64_t PrevLogNumber() const { return prev_log_number_; } + + // Pick level and inputs for a new compaction. + // Returns nullptr if there is no compaction to be done. + // Otherwise returns a pointer to a heap-allocated object that + // describes the compaction. Caller should delete the result. + Compaction* PickCompaction(); + + // Return a compaction object for compacting the range [begin,end] in + // the specified level. Returns nullptr if there is nothing in that + // level that overlaps the specified range. Caller should delete + // the result. + Compaction* CompactRange(int level, const InternalKey* begin, + const InternalKey* end); + + // Return the maximum overlapping data (in bytes) at next level for any + // file at a level >= 1. + int64_t MaxNextLevelOverlappingBytes(); + + // Create an iterator that reads over the compaction inputs for "*c". + // The caller should delete the iterator when no longer needed. + Iterator* MakeInputIterator(Compaction* c); + + // Returns true iff some level needs a compaction. + bool NeedsCompaction() const { + Version* v = current_; + return (v->compaction_score_ >= 1) || (v->file_to_compact_ != nullptr); + } + + // Add all files listed in any live version to *live. + // May also mutate some internal state. + void AddLiveFiles(std::set<uint64_t>* live); + + // Return the approximate offset in the database of the data for + // "key" as of version "v". + uint64_t ApproximateOffsetOf(Version* v, const InternalKey& key); + + // Return a human-readable short (single-line) summary of the number + // of files per level. Uses *scratch as backing store. + struct LevelSummaryStorage { + char buffer[100]; + }; + const char* LevelSummary(LevelSummaryStorage* scratch) const; + + private: + class Builder; + + friend class Compaction; + friend class Version; + + bool ReuseManifest(const std::string& dscname, const std::string& dscbase); + + void Finalize(Version* v); + + void GetRange(const std::vector<FileMetaData*>& inputs, InternalKey* smallest, + InternalKey* largest); + + void GetRange2(const std::vector<FileMetaData*>& inputs1, + const std::vector<FileMetaData*>& inputs2, + InternalKey* smallest, InternalKey* largest); + + void SetupOtherInputs(Compaction* c); + + // Save current contents to *log + Status WriteSnapshot(log::Writer* log); + + void AppendVersion(Version* v); + + Env* const env_; + const std::string dbname_; + const Options* const options_; + TableCache* const table_cache_; + const InternalKeyComparator icmp_; + uint64_t next_file_number_; + uint64_t manifest_file_number_; + uint64_t last_sequence_; + uint64_t log_number_; + uint64_t prev_log_number_; // 0 or backing store for memtable being compacted + + // Opened lazily + WritableFile* descriptor_file_; + log::Writer* descriptor_log_; + Version dummy_versions_; // Head of circular doubly-linked list of versions. + Version* current_; // == dummy_versions_.prev_ + + // Per-level key at which the next compaction at that level should start. + // Either an empty string, or a valid InternalKey. + std::string compact_pointer_[config::kNumLevels]; +}; + +// A Compaction encapsulates information about a compaction. +class Compaction { + public: + ~Compaction(); + + // Return the level that is being compacted. Inputs from "level" + // and "level+1" will be merged to produce a set of "level+1" files. + int level() const { return level_; } + + // Return the object that holds the edits to the descriptor done + // by this compaction. + VersionEdit* edit() { return &edit_; } + + // "which" must be either 0 or 1 + int num_input_files(int which) const { return inputs_[which].size(); } + + // Return the ith input file at "level()+which" ("which" must be 0 or 1). + FileMetaData* input(int which, int i) const { return inputs_[which][i]; } + + // Maximum size of files to build during this compaction. + uint64_t MaxOutputFileSize() const { return max_output_file_size_; } + + // 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; + + // Add all inputs to this compaction as delete operations to *edit. + void AddInputDeletions(VersionEdit* edit); + + // Returns true if the information we have available guarantees that + // 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); + + // Returns true iff we should stop building the current output + // before processing "internal_key". + bool ShouldStopBefore(const Slice& internal_key); + + // Release the input version for the compaction, once the compaction + // is successful. + void ReleaseInputs(); + + private: + friend class Version; + friend class VersionSet; + + Compaction(const Options* options, int level); + + int level_; + uint64_t max_output_file_size_; + Version* input_version_; + VersionEdit edit_; + + // 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 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 + int64_t overlapped_bytes_; // Bytes of overlap between current output + // and grandparent files + + // State for implementing IsBaseLevelForKey + + // 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). + size_t level_ptrs_[config::kNumLevels]; +}; + +} // namespace leveldb + +#endif // STORAGE_LEVELDB_DB_VERSION_SET_H_ |