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diff --git a/src/leveldb/db/version_set.h b/src/leveldb/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 {
+
+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.
+extern 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==NULL represents a key smaller than all keys in the DB.
+// largest==NULL represents a key largest than all keys in the DB.
+// REQUIRES: If disjoint_sorted_files, files[] contains disjoint ranges
+//           in sorted order.
+extern 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:
+  // 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);
+
+  // 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;
+  };
+  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);
+
+  // Reference count management (so Versions do not disappear out from
+  // under live iterators)
+  void Ref();
+  void Unref();
+
+  void GetOverlappingInputs(
+      int level,
+      const InternalKey* begin,         // NULL means before all keys
+      const InternalKey* end,           // NULL 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==NULL represents a key smaller than all keys in the DB.
+  // largest_user_key==NULL represents a key largest than all keys in the DB.
+  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;
+  Iterator* NewConcatenatingIterator(const ReadOptions&, int level) const;
+
+  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_;
+
+  explicit Version(VersionSet* vset)
+      : vset_(vset), next_(this), prev_(this), refs_(0),
+        file_to_compact_(NULL),
+        file_to_compact_level_(-1),
+        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.  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);
+
+  // Recover the last saved descriptor from persistent storage.
+  Status Recover();
+
+  // 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 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 {
+    Version* v = current_;
+    return (v->compaction_score_ >= 1) || (v->file_to_compact_ != NULL);
+  }
+
+  // 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;
+
+  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];
+
+  // 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 "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;
+
+  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_;
+  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_