rocksdb/include/rocksdb/iterator.h
Islam AbdelRahman d719b095dc Introduce PinnedIteratorsManager (Reduce PinData() overhead / Refactor PinData)
Summary:
While trying to reuse PinData() / ReleasePinnedData() .. to optimize away some memcpys I realized that there is a significant overhead for using PinData() / ReleasePinnedData if they were called many times.
This diff refactor the pinning logic by introducing PinnedIteratorsManager a centralized component that will be created once and will be notified whenever we need to Pin an Iterator. This implementation have much less overhead than the original implementation

Test Plan:
make check -j64
COMPILE_WITH_ASAN=1 make check -j64

Reviewers: yhchiang, sdong, andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D56493
2016-04-26 12:41:07 -07:00

126 lines
4.6 KiB
C++

// Copyright (c) 2011-present, 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.
//
// An iterator yields a sequence of key/value pairs from a source.
// The following class defines the interface. Multiple implementations
// are provided by this library. In particular, iterators are provided
// to access the contents of a Table or a DB.
//
// Multiple threads can invoke const methods on an Iterator without
// external synchronization, but if any of the threads may call a
// non-const method, all threads accessing the same Iterator must use
// external synchronization.
#ifndef STORAGE_ROCKSDB_INCLUDE_ITERATOR_H_
#define STORAGE_ROCKSDB_INCLUDE_ITERATOR_H_
#include <string>
#include "rocksdb/slice.h"
#include "rocksdb/status.h"
namespace rocksdb {
class Cleanable {
public:
Cleanable();
~Cleanable();
// Clients are allowed to register function/arg1/arg2 triples that
// will be invoked when this iterator is destroyed.
//
// Note that unlike all of the preceding methods, this method is
// not abstract and therefore clients should not override it.
typedef void (*CleanupFunction)(void* arg1, void* arg2);
void RegisterCleanup(CleanupFunction function, void* arg1, void* arg2);
protected:
struct Cleanup {
CleanupFunction function;
void* arg1;
void* arg2;
Cleanup* next;
};
Cleanup cleanup_;
};
class Iterator : public Cleanable {
public:
Iterator() {}
virtual ~Iterator() {}
// An iterator is either positioned at a key/value pair, or
// not valid. This method returns true iff the iterator is valid.
virtual bool Valid() const = 0;
// Position at the first key in the source. The iterator is Valid()
// after this call iff the source is not empty.
virtual void SeekToFirst() = 0;
// Position at the last key in the source. The iterator is
// Valid() after this call iff the source is not empty.
virtual void SeekToLast() = 0;
// Position at the first key in the source that at or past target
// The iterator is Valid() after this call iff the source contains
// an entry that comes at or past target.
virtual void Seek(const Slice& target) = 0;
// Moves to the next entry in the source. After this call, Valid() is
// true iff the iterator was not positioned at the last entry in the source.
// REQUIRES: Valid()
virtual void Next() = 0;
// Moves to the previous entry in the source. After this call, Valid() is
// true iff the iterator was not positioned at the first entry in source.
// REQUIRES: Valid()
virtual void Prev() = 0;
// Return the key for the current entry. The underlying storage for
// the returned slice is valid only until the next modification of
// the iterator.
// REQUIRES: Valid()
virtual Slice key() const = 0;
// Return the value for the current entry. The underlying storage for
// the returned slice is valid only until the next modification of
// the iterator.
// REQUIRES: !AtEnd() && !AtStart()
virtual Slice value() const = 0;
// If an error has occurred, return it. Else return an ok status.
// If non-blocking IO is requested and this operation cannot be
// satisfied without doing some IO, then this returns Status::Incomplete().
virtual Status status() const = 0;
// Property "rocksdb.iterator.is-key-pinned":
// If returning "1", this means that the Slice returned by key() is valid
// as long as the iterator is not deleted.
// It is guaranteed to always return "1" if
// - Iterator created with ReadOptions::pin_data = true
// - DB tables were created with
// BlockBasedTableOptions::use_delta_encoding = false.
// Property "rocksdb.iterator.super-version-number":
// LSM version used by the iterator. The same format as DB Property
// kCurrentSuperVersionNumber. See its comment for more information.
virtual Status GetProperty(std::string prop_name, std::string* prop);
private:
// No copying allowed
Iterator(const Iterator&);
void operator=(const Iterator&);
};
// Return an empty iterator (yields nothing).
extern Iterator* NewEmptyIterator();
// Return an empty iterator with the specified status.
extern Iterator* NewErrorIterator(const Status& status);
} // namespace rocksdb
#endif // STORAGE_ROCKSDB_INCLUDE_ITERATOR_H_