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256 lines
11 KiB
256 lines
11 KiB
// 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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#ifndef STORAGE_LEVELDB_INCLUDE_DB_H_
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#define STORAGE_LEVELDB_INCLUDE_DB_H_
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#include <stdint.h>
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#include <stdio.h>
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#include <memory>
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#include <vector>
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#include "leveldb/iterator.h"
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#include "leveldb/options.h"
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#include "leveldb/types.h"
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#include "leveldb/transaction_log_iterator.h"
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namespace leveldb {
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using std::unique_ptr;
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// Update Makefile if you change these
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static const int kMajorVersion = 2;
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static const int kMinorVersion = 0;
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struct Options;
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struct ReadOptions;
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struct WriteOptions;
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struct FlushOptions;
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class WriteBatch;
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// Abstract handle to particular state of a DB.
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// A Snapshot is an immutable object and can therefore be safely
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// accessed from multiple threads without any external synchronization.
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class Snapshot {
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protected:
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virtual ~Snapshot();
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};
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// A range of keys
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struct Range {
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Slice start; // Included in the range
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Slice limit; // Not included in the range
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Range() { }
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Range(const Slice& s, const Slice& l) : start(s), limit(l) { }
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};
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// A DB is a persistent ordered map from keys to values.
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// A DB is safe for concurrent access from multiple threads without
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// any external synchronization.
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class DB {
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public:
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// Open the database with the specified "name".
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// Stores a pointer to a heap-allocated database in *dbptr and returns
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// OK on success.
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// Stores nullptr in *dbptr and returns a non-OK status on error.
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// Caller should delete *dbptr when it is no longer needed.
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static Status Open(const Options& options,
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const std::string& name,
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DB** dbptr);
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// Open the database for read only. All DB interfaces
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// that modify data, like put/delete, will return error.
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// If the db is opened in read only mode, then no compactions
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// will happen.
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static Status OpenForReadOnly(const Options& options,
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const std::string& name, DB** dbptr,
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bool error_if_log_file_exist = false);
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DB() { }
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virtual ~DB();
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// Set the database entry for "key" to "value". Returns OK on success,
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// and a non-OK status on error.
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// Note: consider setting options.sync = true.
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virtual Status Put(const WriteOptions& options,
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const Slice& key,
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const Slice& value) = 0;
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// Remove the database entry (if any) for "key". Returns OK on
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// success, and a non-OK status on error. It is not an error if "key"
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// did not exist in the database.
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// Note: consider setting options.sync = true.
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virtual Status Delete(const WriteOptions& options, const Slice& key) = 0;
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// Merge the database entry for "key" with "value". Returns OK on success,
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// and a non-OK status on error. The semantics of this operation is
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// determined by the user provided merge_operator when opening DB.
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// Note: consider setting options.sync = true.
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virtual Status Merge(const WriteOptions& options,
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const Slice& key,
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const Slice& value) = 0;
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// Apply the specified updates to the database.
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// Returns OK on success, non-OK on failure.
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// Note: consider setting options.sync = true.
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virtual Status Write(const WriteOptions& options, WriteBatch* updates) = 0;
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// If the database contains an entry for "key" store the
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// corresponding value in *value and return OK.
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//
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// If there is no entry for "key" leave *value unchanged and return
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// a status for which Status::IsNotFound() returns true.
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//
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// May return some other Status on an error.
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virtual Status Get(const ReadOptions& options,
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const Slice& key, std::string* value) = 0;
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// If keys[i] does not exist in the database, then the i'th returned
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// status will be one for which Status::IsNotFound() is true, and
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// (*values)[i] will be set to some arbitrary value (often ""). Otherwise,
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// the i'th returned status will have Status::ok() true, and (*values)[i]
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// will store the value associated with keys[i].
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//
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// (*values) will always be resized to be the same size as (keys).
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// Similarly, the number of returned statuses will be the number of keys.
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// Note: keys will not be "de-duplicated". Duplicate keys will return
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// duplicate values in order.
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virtual std::vector<Status> MultiGet(const ReadOptions& options,
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const std::vector<Slice>& keys,
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std::vector<std::string>* values) = 0;
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// If the key definitely does not exist in the database, then this method
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// returns false. Otherwise return true. This check is potentially
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// lighter-weight than invoking DB::Get(). No IO is performed
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virtual bool KeyMayExist(const Slice& key) = 0;
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// Return a heap-allocated iterator over the contents of the database.
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// The result of NewIterator() is initially invalid (caller must
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// call one of the Seek methods on the iterator before using it).
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//
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// Caller should delete the iterator when it is no longer needed.
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// The returned iterator should be deleted before this db is deleted.
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virtual Iterator* NewIterator(const ReadOptions& options) = 0;
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// Return a handle to the current DB state. Iterators created with
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// this handle will all observe a stable snapshot of the current DB
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// state. The caller must call ReleaseSnapshot(result) when the
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// snapshot is no longer needed.
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virtual const Snapshot* GetSnapshot() = 0;
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// Release a previously acquired snapshot. The caller must not
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// use "snapshot" after this call.
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virtual void ReleaseSnapshot(const Snapshot* snapshot) = 0;
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// DB implementations can export properties about their state
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// via this method. If "property" is a valid property understood by this
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// DB implementation, fills "*value" with its current value and returns
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// true. Otherwise returns false.
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//
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//
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// Valid property names include:
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//
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// "leveldb.num-files-at-level<N>" - return the number of files at level <N>,
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// where <N> is an ASCII representation of a level number (e.g. "0").
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// "leveldb.stats" - returns a multi-line string that describes statistics
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// about the internal operation of the DB.
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// "leveldb.sstables" - returns a multi-line string that describes all
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// of the sstables that make up the db contents.
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virtual bool GetProperty(const Slice& property, std::string* value) = 0;
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// For each i in [0,n-1], store in "sizes[i]", the approximate
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// file system space used by keys in "[range[i].start .. range[i].limit)".
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//
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// Note that the returned sizes measure file system space usage, so
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// if the user data compresses by a factor of ten, the returned
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// sizes will be one-tenth the size of the corresponding user data size.
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//
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// The results may not include the sizes of recently written data.
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virtual void GetApproximateSizes(const Range* range, int n,
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uint64_t* sizes) = 0;
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// Compact the underlying storage for the key range [*begin,*end].
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// In particular, deleted and overwritten versions are discarded,
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// and the data is rearranged to reduce the cost of operations
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// needed to access the data. This operation should typically only
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// be invoked by users who understand the underlying implementation.
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//
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// begin==nullptr is treated as a key before all keys in the database.
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// end==nullptr is treated as a key after all keys in the database.
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// Therefore the following call will compact the entire database:
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// db->CompactRange(nullptr, nullptr);
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// Note that after the entire database is compacted, all data are pushed
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// down to the last level containing any data. If the total data size
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// after compaction is reduced, that level might not be appropriate for
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// hosting all the files. In this case, client could set reduce_level
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// to true, to move the files back to the minimum level capable of holding
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// the data set.
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virtual void CompactRange(const Slice* begin, const Slice* end,
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bool reduce_level = false) = 0;
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// Number of levels used for this DB.
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virtual int NumberLevels() = 0;
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// Maximum level to which a new compacted memtable is pushed if it
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// does not create overlap.
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virtual int MaxMemCompactionLevel() = 0;
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// Number of files in level-0 that would stop writes.
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virtual int Level0StopWriteTrigger() = 0;
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// Flush all mem-table data.
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virtual Status Flush(const FlushOptions& options) = 0;
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// Prevent file deletions. Compactions will continue to occur,
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// but no obsolete files will be deleted. Calling this multiple
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// times have the same effect as calling it once.
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virtual Status DisableFileDeletions() = 0;
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// Allow compactions to delete obselete files.
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virtual Status EnableFileDeletions() = 0;
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// Retrieve the list of all files in the database. The files are
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// relative to the dbname and are not absolute paths. This list
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// can be used to generate a backup. The valid size of the manifest
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// file is returned in manifest_file_size. The manifest file is
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// an ever growing file, but only the portion specified
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// by manifest_file_size is valid for this snapshot.
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virtual Status GetLiveFiles(std::vector<std::string>&,
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uint64_t* manifest_file_size) = 0;
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// The sequence number of the most recent transaction.
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virtual SequenceNumber GetLatestSequenceNumber() = 0;
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// Return's an iterator for all writes since the sequence number
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// Status::ok if iterator is valid.
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// The iterator internally holds references to the available log files.
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// It automatically takes care of closing a file with no-updates left, and
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// opening the next one.
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// If the sequence number is non existent. it returns an iterator at a seq_no
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// just greater than the requested seq_no.
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// Must set WAL_ttl_seconds to a large value to use this api.
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// else the WAL files will get
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// cleared aggressively and the iterator might keep getting invalid before
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// an update is read.
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virtual Status GetUpdatesSince(SequenceNumber seq_number,
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unique_ptr<TransactionLogIterator>* iter) = 0;
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private:
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// No copying allowed
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DB(const DB&);
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void operator=(const DB&);
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};
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// Destroy the contents of the specified database.
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// Be very careful using this method.
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Status DestroyDB(const std::string& name, const Options& options);
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// If a DB cannot be opened, you may attempt to call this method to
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// resurrect as much of the contents of the database as possible.
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// Some data may be lost, so be careful when calling this function
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// on a database that contains important information.
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Status RepairDB(const std::string& dbname, const Options& options);
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_INCLUDE_DB_H_
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