git-svn-id: https://leveldb.googlecode.com/svn/trunk@12 62dab493-f737-651d-591e-8d6aee1b9529
316 lines
10 KiB
C++
316 lines
10 KiB
C++
// 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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#ifndef STORAGE_LEVELDB_DB_VERSION_SET_H_
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#define STORAGE_LEVELDB_DB_VERSION_SET_H_
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#include <map>
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#include <set>
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#include <vector>
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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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namespace leveldb {
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// Grouping of constants. We may want to make some of these
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// parameters set via options.
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namespace config {
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static const int kNumLevels = 7;
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}
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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 TableBuilder;
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class TableCache;
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class Version;
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class VersionSet;
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class WritableFile;
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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&, std::vector<Iterator*>* iters);
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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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// Return a human readable string that describes this version's contents.
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std::string DebugString() const;
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private:
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friend class Compaction;
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friend class VersionSet;
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class LevelFileNumIterator;
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Iterator* NewConcatenatingIterator(const ReadOptions&, int level) 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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int refs_; // Number of live refs to this version
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MemTable* cleanup_mem_; // NULL, or table to delete when version dropped
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// List of files per level
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std::vector<FileMetaData*> files_[config::kNumLevels];
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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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double compaction_score_;
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int compaction_level_;
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explicit Version(VersionSet* vset)
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: vset_(vset), next_(NULL), refs_(0),
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cleanup_mem_(NULL),
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compaction_score_(-1),
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compaction_level_(-1) {
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}
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~Version();
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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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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. Iff Apply() returns OK, arrange to delete
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// cleanup_mem (if cleanup_mem != NULL) when it is no longer needed
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// by older versions.
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Status LogAndApply(VersionEdit* edit, MemTable* cleanup_mem);
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// Recover the last saved descriptor from persistent storage.
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Status Recover(uint64_t* log_number, SequenceNumber* last_sequence);
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// Save current contents to *log
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Status WriteSnapshot(log::Writer* log);
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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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// Return the number of Table files at the specified level.
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int NumLevelFiles(int level) const;
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// Pick level and inputs for a new compaction.
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// Returns NULL 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 NULL 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 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.
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bool NeedsCompaction() const { return current_->compaction_score_ >= 1; }
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// Add all files listed in any live version to *live.
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// May also mutate some internal state.
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void AddLiveFiles(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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// Register a reference to a large value with the specified
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// large_ref from the specified file number. Returns "true" if this
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// is the first recorded reference to the "large_ref" value in the
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// database, and false otherwise.
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bool RegisterLargeValueRef(const LargeValueRef& large_ref,
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uint64_t filenum,
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const InternalKey& internal_key);
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// Cleanup the large value reference state by eliminating any
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// references from files that are not includes in either "live_tables"
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// or "log_file".
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void CleanupLargeValueRefs(const std::set<uint64_t>& live_tables,
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uint64_t log_file_num);
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// Returns true if a large value with the given reference is live.
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bool LargeValueIsLive(const LargeValueRef& large_ref);
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private:
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class Builder;
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friend class Compaction;
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friend class Version;
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Status Finalize(Version* v);
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// Delete any old versions that are no longer needed.
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void MaybeDeleteOldVersions();
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struct BySmallestKey;
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Status SortLevel(Version* v, uint64_t level);
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void GetOverlappingInputs(
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int level,
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const InternalKey& begin,
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const InternalKey& end,
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std::vector<FileMetaData*>* inputs);
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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 SetupOtherInputs(Compaction* c);
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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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// Opened lazily
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WritableFile* descriptor_file_;
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log::Writer* descriptor_log_;
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// Versions are kept in a singly linked list that is never empty
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Version* current_; // Pointer to the last (newest) list entry
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Version* oldest_; // Pointer to the first (oldest) list entry
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// Map from large value reference to the set of <file numbers,internal_key>
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// values containing references to the value. We keep the
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// internal key as a std::string rather than as an InternalKey because
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// we want to be able to easily use a set.
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typedef std::set<std::pair<uint64_t, std::string> > LargeReferencesSet;
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typedef std::map<LargeValueRef, LargeReferencesSet> LargeValueMap;
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LargeValueMap large_value_refs_;
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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_[config::kNumLevels];
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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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};
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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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// and "level+1" will be merged to produce a set of "level+1" files.
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int level() const { return 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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// Is this a trivial compaction that can be implemented by just
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// moving a single input file to the next level (no merging or splitting)
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bool IsTrivialMove() const;
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// Add all inputs to this compaction as delete operations to *edit.
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void AddInputDeletions(VersionEdit* edit);
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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
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// in levels greater than "level+1".
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bool IsBaseLevelForKey(const Slice& user_key);
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// Returns true iff we should stop building the current output
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// before processing "key".
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bool ShouldStopBefore(const InternalKey& key);
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// Release the input version for the compaction, once the compaction
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// is successful.
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void ReleaseInputs();
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private:
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friend class Version;
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friend class VersionSet;
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explicit Compaction(int level);
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int level_;
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uint64_t max_output_file_size_;
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Version* input_version_;
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VersionEdit edit_;
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// Each compaction reads inputs from "level_" and "level_+1"
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std::vector<FileMetaData*> inputs_[2]; // The two sets of inputs
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// State used to check for number of of overlapping grandparent files
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// (parent == level_ + 1, grandparent == level_ + 2)
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std::vector<FileMetaData*> grandparents_;
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int grandparent_index_; // Index in grandparent_starts_
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int output_start_; // Index in grandparent_starts_ where output started
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// State for implementing IsBaseLevelForKey
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// level_ptrs_ holds indices into input_version_->levels_: our state
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// is that we are positioned at one of the file ranges for each
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// higher level than the ones involved in this compaction (i.e. for
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// all L >= level_ + 2).
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int level_ptrs_[config::kNumLevels];
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};
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}
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#endif // STORAGE_LEVELDB_DB_VERSION_SET_H_
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