rocksdb/include/rocksdb/db.h

// Copyright (c) 2013, Facebook, Inc.  All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
// 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.

#ifndef STORAGE_ROCKSDB_INCLUDE_DB_H_
#define STORAGE_ROCKSDB_INCLUDE_DB_H_

#include <stdint.h>
#include <stdio.h>
#include <memory>
#include <vector>
#include <string>
#include <unordered_map>
#include "rocksdb/immutable_options.h"
#include "rocksdb/iterator.h"
#include "rocksdb/listener.h"
#include "rocksdb/metadata.h"
#include "rocksdb/options.h"
#include "rocksdb/snapshot.h"
#include "rocksdb/thread_status.h"
#include "rocksdb/transaction_log.h"
#include "rocksdb/types.h"
#include "rocksdb/version.h"

#ifdef _WIN32
// Windows API macro interference
#undef DeleteFile
#endif


namespace rocksdb {

struct Options;
struct DBOptions;
struct ColumnFamilyOptions;
struct ReadOptions;
struct WriteOptions;
struct FlushOptions;
struct CompactionOptions;
struct CompactRangeOptions;
struct TableProperties;
struct ExternalSstFileInfo;
class WriteBatch;
class Env;
class EventListener;

using std::unique_ptr;

class ColumnFamilyHandle {
 public:
  virtual ~ColumnFamilyHandle() {}
  virtual const std::string& GetName() const = 0;
  virtual uint32_t GetID() const = 0;
};
extern const std::string kDefaultColumnFamilyName;

struct ColumnFamilyDescriptor {
  std::string name;
  ColumnFamilyOptions options;
  ColumnFamilyDescriptor()
      : name(kDefaultColumnFamilyName), options(ColumnFamilyOptions()) {}
  ColumnFamilyDescriptor(const std::string& _name,
                         const ColumnFamilyOptions& _options)
      : name(_name), options(_options) {}
};

static const int kMajorVersion = __ROCKSDB_MAJOR__;
static const int kMinorVersion = __ROCKSDB_MINOR__;

// A range of keys
struct Range {
  Slice start;          // Included in the range
  Slice limit;          // Not included in the range

  Range() { }
  Range(const Slice& s, const Slice& l) : start(s), limit(l) { }
};

// A collections of table properties objects, where
//  key: is the table's file name.
//  value: the table properties object of the given table.
typedef std::unordered_map<std::string, std::shared_ptr<const TableProperties>>
    TablePropertiesCollection;

// A DB is a persistent ordered map from keys to values.
// A DB is safe for concurrent access from multiple threads without
// any external synchronization.
class DB {
 public:
  // Open the database with the specified "name".
  // Stores a pointer to a heap-allocated database in *dbptr and returns
  // OK on success.
  // Stores nullptr in *dbptr and returns a non-OK status on error.
  // Caller should delete *dbptr when it is no longer needed.
  static Status Open(const Options& options,
                     const std::string& name,
                     DB** dbptr);

  // Open the database for read only. All DB interfaces
  // that modify data, like put/delete, will return error.
  // If the db is opened in read only mode, then no compactions
  // will happen.
  //
  // Not supported in ROCKSDB_LITE, in which case the function will
  // return Status::NotSupported.
  static Status OpenForReadOnly(const Options& options,
      const std::string& name, DB** dbptr,
      bool error_if_log_file_exist = false);

  // Open the database for read only with column families. When opening DB with
  // read only, you can specify only a subset of column families in the
  // database that should be opened. However, you always need to specify default
  // column family. The default column family name is 'default' and it's stored
  // in rocksdb::kDefaultColumnFamilyName
  //
  // Not supported in ROCKSDB_LITE, in which case the function will
  // return Status::NotSupported.
  static Status OpenForReadOnly(
      const DBOptions& db_options, const std::string& name,
      const std::vector<ColumnFamilyDescriptor>& column_families,
      std::vector<ColumnFamilyHandle*>* handles, DB** dbptr,
      bool error_if_log_file_exist = false);

  // Open DB with column families.
  // db_options specify database specific options
  // column_families is the vector of all column families in the database,
  // containing column family name and options. You need to open ALL column
  // families in the database. To get the list of column families, you can use
  // ListColumnFamilies(). Also, you can open only a subset of column families
  // for read-only access.
  // The default column family name is 'default' and it's stored
  // in rocksdb::kDefaultColumnFamilyName.
  // If everything is OK, handles will on return be the same size
  // as column_families --- handles[i] will be a handle that you
  // will use to operate on column family column_family[i]
  static Status Open(const DBOptions& db_options, const std::string& name,
                     const std::vector<ColumnFamilyDescriptor>& column_families,
                     std::vector<ColumnFamilyHandle*>* handles, DB** dbptr);

  // ListColumnFamilies will open the DB specified by argument name
  // and return the list of all column families in that DB
  // through column_families argument. The ordering of
  // column families in column_families is unspecified.
  static Status ListColumnFamilies(const DBOptions& db_options,
                                   const std::string& name,
                                   std::vector<std::string>* column_families);

  DB() { }
  virtual ~DB();

  // Create a column_family and return the handle of column family
  // through the argument handle.
  virtual Status CreateColumnFamily(const ColumnFamilyOptions& options,
                                    const std::string& column_family_name,
                                    ColumnFamilyHandle** handle);

  // Drop a column family specified by column_family handle. This call
  // only records a drop record in the manifest and prevents the column
  // family from flushing and compacting.
  virtual Status DropColumnFamily(ColumnFamilyHandle* column_family);

  // Set the database entry for "key" to "value".
  // If "key" already exists, it will be overwritten.
  // Returns OK on success, and a non-OK status on error.
  // Note: consider setting options.sync = true.
  virtual Status Put(const WriteOptions& options,
                     ColumnFamilyHandle* column_family, const Slice& key,
                     const Slice& value) = 0;
  virtual Status Put(const WriteOptions& options, const Slice& key,
                     const Slice& value) {
    return Put(options, DefaultColumnFamily(), key, value);
  }

  // Remove the database entry (if any) for "key".  Returns OK on
  // success, and a non-OK status on error.  It is not an error if "key"
  // did not exist in the database.
  // Note: consider setting options.sync = true.
  virtual Status Delete(const WriteOptions& options,
                        ColumnFamilyHandle* column_family,
                        const Slice& key) = 0;
  virtual Status Delete(const WriteOptions& options, const Slice& key) {
    return Delete(options, DefaultColumnFamily(), key);
  }

  // Remove the database entry for "key". Requires that the key exists
  // and was not overwritten. Returns OK on success, and a non-OK status
  // on error.  It is not an error if "key" did not exist in the database.
  //
  // If a key is overwritten (by calling Put() multiple times), then the result
  // of calling SingleDelete() on this key is undefined.  SingleDelete() only
  // behaves correctly if there has been only one Put() for this key since the
  // previous call to SingleDelete() for this key.
  //
  // This feature is currently an experimental performance optimization
  // for a very specific workload.  It is up to the caller to ensure that
  // SingleDelete is only used for a key that is not deleted using Delete() or
  // written using Merge().  Mixing SingleDelete operations with Deletes and
  // Merges can result in undefined behavior.
  //
  // Note: consider setting options.sync = true.
  virtual Status SingleDelete(const WriteOptions& options,
                              ColumnFamilyHandle* column_family,
                              const Slice& key) = 0;
  virtual Status SingleDelete(const WriteOptions& options, const Slice& key) {
    return SingleDelete(options, DefaultColumnFamily(), key);
  }

  // Merge the database entry for "key" with "value".  Returns OK on success,
  // and a non-OK status on error. The semantics of this operation is
  // determined by the user provided merge_operator when opening DB.
  // Note: consider setting options.sync = true.
  virtual Status Merge(const WriteOptions& options,
                       ColumnFamilyHandle* column_family, const Slice& key,
                       const Slice& value) = 0;
  virtual Status Merge(const WriteOptions& options, const Slice& key,
                       const Slice& value) {
    return Merge(options, DefaultColumnFamily(), key, value);
  }

  // Apply the specified updates to the database.
  // If `updates` contains no update, WAL will still be synced if
  // options.sync=true.
  // Returns OK on success, non-OK on failure.
  // Note: consider setting options.sync = true.
  virtual Status Write(const WriteOptions& options, WriteBatch* updates) = 0;

  // If the database contains an entry for "key" store the
  // corresponding value in *value and return OK.
  //
  // If there is no entry for "key" leave *value unchanged and return
  // a status for which Status::IsNotFound() returns true.
  //
  // May return some other Status on an error.
  virtual Status Get(const ReadOptions& options,
                     ColumnFamilyHandle* column_family, const Slice& key,
                     std::string* value) = 0;
  virtual Status Get(const ReadOptions& options, const Slice& key, std::string* value) {
    return Get(options, DefaultColumnFamily(), key, value);
  }

  // If keys[i] does not exist in the database, then the i'th returned
  // status will be one for which Status::IsNotFound() is true, and
  // (*values)[i] will be set to some arbitrary value (often ""). Otherwise,
  // the i'th returned status will have Status::ok() true, and (*values)[i]
  // will store the value associated with keys[i].
  //
  // (*values) will always be resized to be the same size as (keys).
  // Similarly, the number of returned statuses will be the number of keys.
  // Note: keys will not be "de-duplicated". Duplicate keys will return
  // duplicate values in order.
  virtual std::vector<Status> MultiGet(
      const ReadOptions& options,
      const std::vector<ColumnFamilyHandle*>& column_family,
      const std::vector<Slice>& keys, std::vector<std::string>* values) = 0;
  virtual std::vector<Status> MultiGet(const ReadOptions& options,
                                       const std::vector<Slice>& keys,
                                       std::vector<std::string>* values) {
    return MultiGet(options, std::vector<ColumnFamilyHandle*>(
                                 keys.size(), DefaultColumnFamily()),
                    keys, values);
  }

  // If the key definitely does not exist in the database, then this method
  // returns false, else true. If the caller wants to obtain value when the key
  // is found in memory, a bool for 'value_found' must be passed. 'value_found'
  // will be true on return if value has been set properly.
  // This check is potentially lighter-weight than invoking DB::Get(). One way
  // to make this lighter weight is to avoid doing any IOs.
  // Default implementation here returns true and sets 'value_found' to false
  virtual bool KeyMayExist(const ReadOptions& /*options*/,
                           ColumnFamilyHandle* /*column_family*/,
                           const Slice& /*key*/, std::string* /*value*/,
                           bool* value_found = nullptr) {
    if (value_found != nullptr) {
      *value_found = false;
    }
    return true;
  }
  virtual bool KeyMayExist(const ReadOptions& options, const Slice& key,
                           std::string* value, bool* value_found = nullptr) {
    return KeyMayExist(options, DefaultColumnFamily(), key, value, value_found);
  }

  // Return a heap-allocated iterator over the contents of the database.
  // The result of NewIterator() is initially invalid (caller must
  // call one of the Seek methods on the iterator before using it).
  //
  // Caller should delete the iterator when it is no longer needed.
  // The returned iterator should be deleted before this db is deleted.
  virtual Iterator* NewIterator(const ReadOptions& options,
                                ColumnFamilyHandle* column_family) = 0;
  virtual Iterator* NewIterator(const ReadOptions& options) {
    return NewIterator(options, DefaultColumnFamily());
  }
  // Returns iterators from a consistent database state across multiple
  // column families. Iterators are heap allocated and need to be deleted
  // before the db is deleted
  virtual Status NewIterators(
      const ReadOptions& options,
      const std::vector<ColumnFamilyHandle*>& column_families,
      std::vector<Iterator*>* iterators) = 0;

  // Return a handle to the current DB state.  Iterators created with
  // this handle will all observe a stable snapshot of the current DB
  // state.  The caller must call ReleaseSnapshot(result) when the
  // snapshot is no longer needed.
  //
  // nullptr will be returned if the DB fails to take a snapshot or does
  // not support snapshot.
  virtual const Snapshot* GetSnapshot() = 0;

  // Release a previously acquired snapshot.  The caller must not
  // use "snapshot" after this call.
  virtual void ReleaseSnapshot(const Snapshot* snapshot) = 0;

  // DB implementations can export properties about their state
  // via this method.  If "property" is a valid property understood by this
  // DB implementation, fills "*value" with its current value and returns
  // true.  Otherwise returns false.
  //
  //
  // Valid property names include:
  //
  //  "rocksdb.num-files-at-level<N>" - return the number of files at level <N>,
  //     where <N> is an ASCII representation of a level number (e.g. "0").
  //  "rocksdb.stats" - returns a multi-line string that describes statistics
  //     about the internal operation of the DB.
  //  "rocksdb.sstables" - returns a multi-line string that describes all
  //     of the sstables that make up the db contents.
  //  "rocksdb.cfstats"
  //  "rocksdb.dbstats"
  //  "rocksdb.num-immutable-mem-table"
  //  "rocksdb.mem-table-flush-pending"
  //  "rocksdb.compaction-pending" - 1 if at least one compaction is pending
  //  "rocksdb.background-errors" - accumulated number of background errors
  //  "rocksdb.cur-size-active-mem-table"
  //  "rocksdb.size-all-mem-tables"
  //  "rocksdb.num-entries-active-mem-table"
  //  "rocksdb.num-entries-imm-mem-tables"
  //  "rocksdb.num-deletes-active-mem-table"
  //  "rocksdb.num-deletes-imm-mem-tables"
  //  "rocksdb.estimate-num-keys" - estimated keys in the column family
  //  "rocksdb.estimate-table-readers-mem" - estimated memory used for reding
  //      SST tables, that is not counted as a part of block cache.
  //  "rocksdb.is-file-deletions-enabled"
  //  "rocksdb.num-snapshots"
  //  "rocksdb.oldest-snapshot-time"
  //  "rocksdb.num-live-versions" - `version` is an internal data structure.
  //      See version_set.h for details. More live versions often mean more SST
  //      files are held from being deleted, by iterators or unfinished
  //      compactions.
  //  "rocksdb.estimate-live-data-size"
  //  "rocksdb.total-sst-files-size" - total size of all used sst files, this
  //      may slow down online queries if there are too many files.
  //  "rocksdb.base-level"
  //  "rocksdb.estimate-pending-compaction-bytes" - estimated total number of
  //      bytes compaction needs to rewrite the data to get all levels down
  //      to under target size. Not valid for other compactions than
  //      level-based.
  //  "rocksdb.aggregated-table-properties" - returns a string representation
  //      of the aggregated table properties of the target column family.
  //  "rocksdb.aggregated-table-properties-at-level<N>", same as the previous
  //      one but only returns the aggregated table properties of the specified
  //      level "N" at the target column family.
  //  "rocksdb.num-running-compactions" - the number of currently running
  //      compacitons.
  //  "rocksdb.num-running-flushes" - the number of currently running flushes.
#ifndef ROCKSDB_LITE
  struct Properties {
    static const std::string kNumFilesAtLevelPrefix;
    static const std::string kStats;
    static const std::string kSSTables;
    static const std::string kCFStats;
    static const std::string kDBStats;
    static const std::string kNumImmutableMemTable;
    static const std::string kMemTableFlushPending;
    static const std::string kNumRunningFlushes;
    static const std::string kCompactionPending;
    static const std::string kNumRunningCompactions;
    static const std::string kBackgroundErrors;
    static const std::string kCurSizeActiveMemTable;
    static const std::string kCurSizeAllMemTables;
    static const std::string kSizeAllMemTables;
    static const std::string kNumEntriesActiveMemTable;
    static const std::string kNumEntriesImmMemTables;
    static const std::string kNumDeletesActiveMemTable;
    static const std::string kNumDeletesImmMemTables;
    static const std::string kEstimateNumKeys;
    static const std::string kEstimateTableReadersMem;
    static const std::string kIsFileDeletionsEnabled;
    static const std::string kNumSnapshots;
    static const std::string kOldestSnapshotTime;
    static const std::string kNumLiveVersions;
    static const std::string kEstimateLiveDataSize;
    static const std::string kTotalSstFilesSize;
    static const std::string kEstimatePendingCompactionBytes;
    static const std::string kAggregatedTableProperties;
    static const std::string kAggregatedTablePropertiesAtLevel;
  };
#endif /* ROCKSDB_LITE */

  virtual bool GetProperty(ColumnFamilyHandle* column_family,
                           const Slice& property, std::string* value) = 0;
  virtual bool GetProperty(const Slice& property, std::string* value) {
    return GetProperty(DefaultColumnFamily(), property, value);
  }

  // Similar to GetProperty(), but only works for a subset of properties whose
  // return value is an integer. Return the value by integer. Supported
  // properties:
  //  "rocksdb.num-immutable-mem-table"
  //  "rocksdb.mem-table-flush-pending"
  //  "rocksdb.compaction-pending"
  //  "rocksdb.background-errors"
  //  "rocksdb.cur-size-active-mem-table"
  //  "rocksdb.cur-size-all-mem-tables"
  //  "rocksdb.size-all-mem-tables"
  //  "rocksdb.num-entries-active-mem-table"
  //  "rocksdb.num-entries-imm-mem-tables"
  //  "rocksdb.num-deletes-active-mem-table"
  //  "rocksdb.num-deletes-imm-mem-tables"
  //  "rocksdb.estimate-num-keys"
  //  "rocksdb.estimate-table-readers-mem"
  //  "rocksdb.is-file-deletions-enabled"
  //  "rocksdb.num-snapshots"
  //  "rocksdb.oldest-snapshot-time"
  //  "rocksdb.num-live-versions"
  //  "rocksdb.estimate-live-data-size"
  //  "rocksdb.total-sst-files-size"
  //  "rocksdb.base-level"
  //  "rocksdb.estimate-pending-compaction-bytes"
  //  "rocksdb.num-running-compactions"
  //  "rocksdb.num-running-flushes"
  virtual bool GetIntProperty(ColumnFamilyHandle* column_family,
                              const Slice& property, uint64_t* value) = 0;
  virtual bool GetIntProperty(const Slice& property, uint64_t* value) {
    return GetIntProperty(DefaultColumnFamily(), property, value);
  }

  // Same as GetIntProperty(), but this one returns the aggregated int
  // property from all column families.
  virtual bool GetAggregatedIntProperty(const Slice& property,
                                        uint64_t* value) = 0;

  // For each i in [0,n-1], store in "sizes[i]", the approximate
  // file system space used by keys in "[range[i].start .. range[i].limit)".
  //
  // Note that the returned sizes measure file system space usage, so
  // if the user data compresses by a factor of ten, the returned
  // sizes will be one-tenth the size of the corresponding user data size.
  //
  // If include_memtable is set to true, then the result will also
  // include those recently written data in the mem-tables if
  // the mem-table type supports it.
  virtual void GetApproximateSizes(ColumnFamilyHandle* column_family,
                                   const Range* range, int n, uint64_t* sizes,
                                   bool include_memtable = false) = 0;
  virtual void GetApproximateSizes(const Range* range, int n, uint64_t* sizes,
                                   bool include_memtable = false) {
    GetApproximateSizes(DefaultColumnFamily(), range, n, sizes,
                        include_memtable);
  }

  // Compact the underlying storage for the key range [*begin,*end].
  // The actual compaction interval might be superset of [*begin, *end].
  // In particular, deleted and overwritten versions are discarded,
  // and the data is rearranged to reduce the cost of operations
  // needed to access the data.  This operation should typically only
  // be invoked by users who understand the underlying implementation.
  //
  // begin==nullptr is treated as a key before all keys in the database.
  // end==nullptr is treated as a key after all keys in the database.
  // Therefore the following call will compact the entire database:
  //    db->CompactRange(options, nullptr, nullptr);
  // Note that after the entire database is compacted, all data are pushed
  // down to the last level containing any data. If the total data size after
  // compaction is reduced, that level might not be appropriate for hosting all
  // the files. In this case, client could set options.change_level to true, to
  // move the files back to the minimum level capable of holding the data set
  // or a given level (specified by non-negative options.target_level).
  virtual Status CompactRange(const CompactRangeOptions& options,
                              ColumnFamilyHandle* column_family,
                              const Slice* begin, const Slice* end) = 0;
  virtual Status CompactRange(const CompactRangeOptions& options,
                              const Slice* begin, const Slice* end) {
    return CompactRange(options, DefaultColumnFamily(), begin, end);
  }

#if defined(__GNUC__) || defined(__clang__)
  __attribute__((deprecated))
#elif _WIN32
  __declspec(deprecated)
#endif
   virtual Status
      CompactRange(ColumnFamilyHandle* column_family, const Slice* begin,
                   const Slice* end, bool change_level = false,
                   int target_level = -1, uint32_t target_path_id = 0) {
    CompactRangeOptions options;
    options.change_level = change_level;
    options.target_level = target_level;
    options.target_path_id = target_path_id;
    return CompactRange(options, column_family, begin, end);
  }
#if defined(__GNUC__) || defined(__clang__)
  __attribute__((deprecated))
#elif _WIN32
  __declspec(deprecated)
#endif
    virtual Status
      CompactRange(const Slice* begin, const Slice* end,
                   bool change_level = false, int target_level = -1,
                   uint32_t target_path_id = 0) {
    CompactRangeOptions options;
    options.change_level = change_level;
    options.target_level = target_level;
    options.target_path_id = target_path_id;
    return CompactRange(options, DefaultColumnFamily(), begin, end);
  }

  virtual Status SetOptions(
      ColumnFamilyHandle* /*column_family*/,
      const std::unordered_map<std::string, std::string>& /*new_options*/) {
    return Status::NotSupported("Not implemented");
  }
  virtual Status SetOptions(
      const std::unordered_map<std::string, std::string>& new_options) {
    return SetOptions(DefaultColumnFamily(), new_options);
  }

  // CompactFiles() inputs a list of files specified by file numbers and
  // compacts them to the specified level. Note that the behavior is different
  // from CompactRange() in that CompactFiles() performs the compaction job
  // using the CURRENT thread.
  //
  // @see GetDataBaseMetaData
  // @see GetColumnFamilyMetaData
  virtual Status CompactFiles(
      const CompactionOptions& compact_options,
      ColumnFamilyHandle* column_family,
      const std::vector<std::string>& input_file_names,
      const int output_level, const int output_path_id = -1) = 0;

  virtual Status CompactFiles(
      const CompactionOptions& compact_options,
      const std::vector<std::string>& input_file_names,
      const int output_level, const int output_path_id = -1) {
    return CompactFiles(compact_options, DefaultColumnFamily(),
                        input_file_names, output_level, output_path_id);
  }

  // This function will wait until all currently running background processes
  // finish. After it returns, no background process will be run until
  // UnblockBackgroundWork is called
  virtual Status PauseBackgroundWork() = 0;
  virtual Status ContinueBackgroundWork() = 0;

  // Number of levels used for this DB.
  virtual int NumberLevels(ColumnFamilyHandle* column_family) = 0;
  virtual int NumberLevels() { return NumberLevels(DefaultColumnFamily()); }

  // Maximum level to which a new compacted memtable is pushed if it
  // does not create overlap.
  virtual int MaxMemCompactionLevel(ColumnFamilyHandle* column_family) = 0;
  virtual int MaxMemCompactionLevel() {
    return MaxMemCompactionLevel(DefaultColumnFamily());
  }

  // Number of files in level-0 that would stop writes.
  virtual int Level0StopWriteTrigger(ColumnFamilyHandle* column_family) = 0;
  virtual int Level0StopWriteTrigger() {
    return Level0StopWriteTrigger(DefaultColumnFamily());
  }

  // Get DB name -- the exact same name that was provided as an argument to
  // DB::Open()
  virtual const std::string& GetName() const = 0;

  // Get Env object from the DB
  virtual Env* GetEnv() const = 0;

  // Get DB Options that we use.  During the process of opening the
  // column family, the options provided when calling DB::Open() or
  // DB::CreateColumnFamily() will have been "sanitized" and transformed
  // in an implementation-defined manner.
  virtual const Options& GetOptions(ColumnFamilyHandle* column_family)
      const = 0;
  virtual const Options& GetOptions() const {
    return GetOptions(DefaultColumnFamily());
  }

  virtual const DBOptions& GetDBOptions() const = 0;

  // Flush all mem-table data.
  virtual Status Flush(const FlushOptions& options,
                       ColumnFamilyHandle* column_family) = 0;
  virtual Status Flush(const FlushOptions& options) {
    return Flush(options, DefaultColumnFamily());
  }

  // Sync the wal. Note that Write() followed by SyncWAL() is not exactly the
  // same as Write() with sync=true: in the latter case the changes won't be
  // visible until the sync is done.
  // Currently only works if allow_mmap_writes = false in Options.
  virtual Status SyncWAL() = 0;

  // The sequence number of the most recent transaction.
  virtual SequenceNumber GetLatestSequenceNumber() const = 0;

#ifndef ROCKSDB_LITE

  // Prevent file deletions. Compactions will continue to occur,
  // but no obsolete files will be deleted. Calling this multiple
  // times have the same effect as calling it once.
  virtual Status DisableFileDeletions() = 0;

  // Allow compactions to delete obsolete files.
  // If force == true, the call to EnableFileDeletions() will guarantee that
  // file deletions are enabled after the call, even if DisableFileDeletions()
  // was called multiple times before.
  // If force == false, EnableFileDeletions will only enable file deletion
  // after it's been called at least as many times as DisableFileDeletions(),
  // enabling the two methods to be called by two threads concurrently without
  // synchronization -- i.e., file deletions will be enabled only after both
  // threads call EnableFileDeletions()
  virtual Status EnableFileDeletions(bool force = true) = 0;

  // GetLiveFiles followed by GetSortedWalFiles can generate a lossless backup

  // Retrieve the list of all files in the database. The files are
  // relative to the dbname and are not absolute paths. The valid size of the
  // manifest file is returned in manifest_file_size. The manifest file is an
  // ever growing file, but only the portion specified by manifest_file_size is
  // valid for this snapshot.
  // Setting flush_memtable to true does Flush before recording the live files.
  // Setting flush_memtable to false is useful when we don't want to wait for
  // flush which may have to wait for compaction to complete taking an
  // indeterminate time.
  //
  // In case you have multiple column families, even if flush_memtable is true,
  // you still need to call GetSortedWalFiles after GetLiveFiles to compensate
  // for new data that arrived to already-flushed column families while other
  // column families were flushing
  virtual Status GetLiveFiles(std::vector<std::string>&,
                              uint64_t* manifest_file_size,
                              bool flush_memtable = true) = 0;

  // Retrieve the sorted list of all wal files with earliest file first
  virtual Status GetSortedWalFiles(VectorLogPtr& files) = 0;

  // Sets iter to an iterator that is positioned at a write-batch containing
  // seq_number. If the sequence number is non existent, it returns an iterator
  // at the first available seq_no after the requested seq_no
  // Returns Status::OK if iterator is valid
  // Must set WAL_ttl_seconds or WAL_size_limit_MB to large values to
  // use this api, else the WAL files will get
  // cleared aggressively and the iterator might keep getting invalid before
  // an update is read.
  virtual Status GetUpdatesSince(
      SequenceNumber seq_number, unique_ptr<TransactionLogIterator>* iter,
      const TransactionLogIterator::ReadOptions&
          read_options = TransactionLogIterator::ReadOptions()) = 0;

// Windows API macro interference
#undef DeleteFile
  // Delete the file name from the db directory and update the internal state to
  // reflect that. Supports deletion of sst and log files only. 'name' must be
  // path relative to the db directory. eg. 000001.sst, /archive/000003.log
  virtual Status DeleteFile(std::string name) = 0;

  // Returns a list of all table files with their level, start key
  // and end key
  virtual void GetLiveFilesMetaData(
      std::vector<LiveFileMetaData>* /*metadata*/) {}

  // Obtains the meta data of the specified column family of the DB.
  // Status::NotFound() will be returned if the current DB does not have
  // any column family match the specified name.
  //
  // If cf_name is not specified, then the metadata of the default
  // column family will be returned.
  virtual void GetColumnFamilyMetaData(ColumnFamilyHandle* /*column_family*/,
                                       ColumnFamilyMetaData* /*metadata*/) {}

  // Get the metadata of the default column family.
  void GetColumnFamilyMetaData(
      ColumnFamilyMetaData* metadata) {
    GetColumnFamilyMetaData(DefaultColumnFamily(), metadata);
  }

  // Load table file located at "file_path" into "column_family", a pointer to
  // ExternalSstFileInfo can be used instead of "file_path" to do a blind add
  // that wont need to read the file, move_file can be set to true to
  // move the file instead of copying it.
  //
  // Current Requirements:
  // (1) Key range in loaded table file don't overlap with
  //     existing keys or tombstones in DB.
  // (2) No other writes happen during AddFile call, otherwise
  //     DB may get corrupted.
  // (3) No snapshots are held.
  virtual Status AddFile(ColumnFamilyHandle* column_family,
                         const std::string& file_path,
                         bool move_file = false) = 0;
  virtual Status AddFile(const std::string& file_path, bool move_file = false) {
    return AddFile(DefaultColumnFamily(), file_path, move_file);
  }

  // Load table file with information "file_info" into "column_family"
  virtual Status AddFile(ColumnFamilyHandle* column_family,
                         const ExternalSstFileInfo* file_info,
                         bool move_file = false) = 0;
  virtual Status AddFile(const ExternalSstFileInfo* file_info,
                         bool move_file = false) {
    return AddFile(DefaultColumnFamily(), file_info, move_file);
  }

#endif  // ROCKSDB_LITE

  // Sets the globally unique ID created at database creation time by invoking
  // Env::GenerateUniqueId(), in identity. Returns Status::OK if identity could
  // be set properly
  virtual Status GetDbIdentity(std::string& identity) const = 0;

  // Returns default column family handle
  virtual ColumnFamilyHandle* DefaultColumnFamily() const = 0;

#ifndef ROCKSDB_LITE
  virtual Status GetPropertiesOfAllTables(ColumnFamilyHandle* column_family,
                                          TablePropertiesCollection* props) = 0;
  virtual Status GetPropertiesOfAllTables(TablePropertiesCollection* props) {
    return GetPropertiesOfAllTables(DefaultColumnFamily(), props);
  }
  virtual Status GetPropertiesOfTablesInRange(
      ColumnFamilyHandle* column_family, const Range* range, std::size_t n,
      TablePropertiesCollection* props) = 0;
#endif  // ROCKSDB_LITE

  // Needed for StackableDB
  virtual DB* GetRootDB() { return this; }

 private:
  // No copying allowed
  DB(const DB&);
  void operator=(const DB&);
};

// Destroy the contents of the specified database.
// Be very careful using this method.
Status DestroyDB(const std::string& name, const Options& options);

#ifndef ROCKSDB_LITE
// If a DB cannot be opened, you may attempt to call this method to
// resurrect as much of the contents of the database as possible.
// Some data may be lost, so be careful when calling this function
// on a database that contains important information.
Status RepairDB(const std::string& dbname, const Options& options);
#endif

}  // namespace rocksdb

#endif  // STORAGE_ROCKSDB_INCLUDE_DB_H_