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148 lines
5.5 KiB
148 lines
5.5 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 "leveldb/iterator.h"
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#include "leveldb/options.h"
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namespace leveldb {
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static const int kMajorVersion = 1;
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static const int kMinorVersion = 2;
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struct Options;
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struct ReadOptions;
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struct WriteOptions;
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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(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 NULL 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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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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// 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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// 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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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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// Possible extensions:
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// (1) Add a method to compact a range of keys
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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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}
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#endif // STORAGE_LEVELDB_INCLUDE_DB_H_
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