rocksdb/db/memtablelist.h

// Copyright (c) 2012 Facebook.

#ifndef STORAGE_LEVELDB_DB_MEMTABLELIST_H_
#define STORAGE_LEVELDB_DB_MEMTABLELIST_H_

#include <string>
#include <list>
#include "leveldb/db.h"
#include "db/dbformat.h"
#include "db/skiplist.h"
#include "util/arena.h"
#include "memtable.h"

namespace leveldb {

class InternalKeyComparator;
class Mutex;
class MemTableListIterator;

//
// This class stores refeernces to all the immutable memtables.
// The memtables are flushed to L0 as soon as possible and in
// any order. If there are more than one immutable memtable, their
// flushes can occur concurrently.  However, they are 'committed'
// to the manifest in FIFO order to maintain correctness and
// recoverability from a crash.
//
class MemTableList {
 public:
  // A list of memtables.
  MemTableList() : size_(0), num_flush_not_started_(0),
    commit_in_progress_(false) {
    imm_flush_needed.Release_Store(nullptr);
  }
  ~MemTableList() {};

  // so that backgrund threads can detect non-nullptr pointer to
  // determine whether this is anything more to start flushing.
  port::AtomicPointer imm_flush_needed;

  // Increase reference count on all underling memtables
  void RefAll();

  // Drop reference count on all underling memtables
  void UnrefAll();

  // Returns the total number of memtables in the list
  int size();

  // Returns true if there is at least one memtable on which flush has
  // not yet started.
  bool IsFlushPending();

  // Returns the earliest memtable that needs to be flushed.
  // Returns null, if no such memtable exist.
  MemTable* PickMemtableToFlush();

  // Commit a successful flush in the manifest file
  Status InstallMemtableFlushResults(MemTable* m,
                      VersionSet* vset, Status flushStatus,
                      port::Mutex* mu, Logger* info_log,
                      uint64_t file_number,
                      std::set<uint64_t>& pending_outputs);

  // New memtables are inserted at the front of the list.
  // Takes ownership of the referenced held on *m by the caller of Add().
  void Add(MemTable* m);

  // Returns an estimate of the number of bytes of data in use.
  size_t ApproximateMemoryUsage();

  // Search all the memtables starting from the most recent one.
  // Return the most recent value found, if any.
  bool Get(const LookupKey& key, std::string* value, Status* s,
           const Options& options);

  // Returns the list of underlying memtables.
  void GetMemTables(std::vector<MemTable*>* list);

  // Copying allowed
  // MemTableList(const MemTableList&);
  // void operator=(const MemTableList&);

 private:
  std::list<MemTable*> memlist_;
  int size_;

  // the number of elements that still need flushing
  int num_flush_not_started_;

  // committing in progress
  bool commit_in_progress_;

};

}  // namespace leveldb

#endif  // STORAGE_LEVELDB_DB_MEMTABLELIST_H_