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rocksdb/db/version_set.h

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// 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"
namespace leveldb {
// Grouping of constants. We may want to make some of these
// parameters set via options.
namespace config {
static const int kNumLevels = 7;
}
namespace log { class Writer; }
class Compaction;
class Iterator;
class MemTable;
class TableBuilder;
class TableCache;
class Version;
class VersionSet;
class WritableFile;
class Version {
public:
// 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);
// Reference count management (so Versions do not disappear out from
// under live iterators)
void Ref();
void Unref();
// Return a human readable string that describes this version's contents.
std::string DebugString() const;
private:
friend class Compaction;
friend class VersionSet;
class LevelFileNumIterator;
Iterator* NewConcatenatingIterator(const ReadOptions&, int level) const;
VersionSet* vset_; // VersionSet to which this Version belongs
Version* next_; // Next version in linked list
int refs_; // Number of live refs to this version
MemTable* cleanup_mem_; // NULL, or table to delete when version dropped
// List of files per level
std::vector<FileMetaData*> files_[config::kNumLevels];
// 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_;
explicit Version(VersionSet* vset)
: vset_(vset), next_(NULL), refs_(0),
cleanup_mem_(NULL),
compaction_score_(-1),
compaction_level_(-1) {
}
~Version();
// No copying allowed
Version(const Version&);
void operator=(const Version&);
};
class VersionSet {
public:
VersionSet(const std::string& dbname,
const Options* options,
TableCache* table_cache,
const InternalKeyComparator*);
~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. Iff Apply() returns OK, arrange to delete
// cleanup_mem (if cleanup_mem != NULL) when it is no longer needed
// by older versions.
Status LogAndApply(VersionEdit* edit, MemTable* cleanup_mem);
// Recover the last saved descriptor from persistent storage.
Status Recover(uint64_t* log_number, SequenceNumber* last_sequence);
// Save current contents to *log
Status WriteSnapshot(log::Writer* log);
// 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_++; }
// Return the number of Table files at the specified level.
int NumLevelFiles(int level) const;
// Pick level and inputs for a new compaction.
// Returns NULL 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 NULL 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 { return current_->compaction_score_ >= 1; }
// 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);
// Register a reference to a large value with the specified
// large_ref from the specified file number. Returns "true" if this
// is the first recorded reference to the "large_ref" value in the
// database, and false otherwise.
bool RegisterLargeValueRef(const LargeValueRef& large_ref,
uint64_t filenum,
const InternalKey& internal_key);
// Cleanup the large value reference state by eliminating any
// references from files that are not includes in either "live_tables"
// or "log_file".
void CleanupLargeValueRefs(const std::set<uint64_t>& live_tables,
uint64_t log_file_num);
// Returns true if a large value with the given reference is live.
bool LargeValueIsLive(const LargeValueRef& large_ref);
private:
class Builder;
friend class Compaction;
friend class Version;
Status Finalize(Version* v);
// Delete any old versions that are no longer needed.
void MaybeDeleteOldVersions();
struct BySmallestKey;
Status SortLevel(Version* v, uint64_t level);
void GetOverlappingInputs(
int level,
const InternalKey& begin,
const InternalKey& end,
std::vector<FileMetaData*>* inputs);
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);
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_;
// Opened lazily
WritableFile* descriptor_file_;
log::Writer* descriptor_log_;
// Versions are kept in a singly linked list that is never empty
Version* current_; // Pointer to the last (newest) list entry
Version* oldest_; // Pointer to the first (oldest) list entry
// Map from large value reference to the set of <file numbers,internal_key>
// values containing references to the value. We keep the
// internal key as a std::string rather than as an InternalKey because
// we want to be able to easily use a set.
typedef std::set<std::pair<uint64_t, std::string> > LargeReferencesSet;
typedef std::map<LargeValueRef, LargeReferencesSet> LargeValueMap;
LargeValueMap large_value_refs_;
// 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];
// No copying allowed
VersionSet(const VersionSet&);
void operator=(const VersionSet&);
};
// 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 "key".
bool ShouldStopBefore(const InternalKey& key);
// Release the input version for the compaction, once the compaction
// is successful.
void ReleaseInputs();
private:
friend class Version;
friend class VersionSet;
explicit Compaction(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 of overlapping grandparent files
// (parent == level_ + 1, grandparent == level_ + 2)
std::vector<FileMetaData*> grandparents_;
int 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).
int level_ptrs_[config::kNumLevels];
};
}
#endif // STORAGE_LEVELDB_DB_VERSION_SET_H_