11526252cc
Summary:
PinnableSlice
Summary:
Currently the point lookup values are copied to a string provided by the
user. This incures an extra memcpy cost. This patch allows doing point lookup
via a PinnableSlice which pins the source memory location (instead of
copying their content) and releases them after the content is consumed
by the user. The old API of Get(string) is translated to the new API
underneath.
Here is the summary for improvements:
value 100 byte: 1.8% regular, 1.2% merge values
value 1k byte: 11.5% regular, 7.5% merge values
value 10k byte: 26% regular, 29.9% merge values
The improvement for merge could be more if we extend this approach to
pin the merge output and delay the full merge operation until the user
actually needs it. We have put that for future work.
PS:
Sometimes we observe a small decrease in performance when switching from
t5452014 to this patch but with the old Get(string) API. The d
Closes https://github.com/facebook/rocksdb/pull/1756
Differential Revision: D4391738
Pulled By: maysamyabandeh
fbshipit-source-id: 6f3edd3
110 lines
4.3 KiB
C++
110 lines
4.3 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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// 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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//
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// An iterator yields a sequence of key/value pairs from a source.
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// The following class defines the interface. Multiple implementations
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// are provided by this library. In particular, iterators are provided
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// to access the contents of a Table or a DB.
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//
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// Multiple threads can invoke const methods on an Iterator without
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// external synchronization, but if any of the threads may call a
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// non-const method, all threads accessing the same Iterator must use
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// external synchronization.
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#ifndef STORAGE_ROCKSDB_INCLUDE_ITERATOR_H_
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#define STORAGE_ROCKSDB_INCLUDE_ITERATOR_H_
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#include <string>
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#include "rocksdb/cleanable.h"
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#include "rocksdb/slice.h"
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#include "rocksdb/status.h"
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namespace rocksdb {
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class Iterator : public Cleanable {
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public:
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Iterator() {}
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virtual ~Iterator() {}
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// An iterator is either positioned at a key/value pair, or
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// not valid. This method returns true iff the iterator is valid.
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virtual bool Valid() const = 0;
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// Position at the first key in the source. The iterator is Valid()
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// after this call iff the source is not empty.
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virtual void SeekToFirst() = 0;
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// Position at the last key in the source. The iterator is
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// Valid() after this call iff the source is not empty.
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virtual void SeekToLast() = 0;
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// Position at the first key in the source that at or past target
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// The iterator is Valid() after this call iff the source contains
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// an entry that comes at or past target.
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virtual void Seek(const Slice& target) = 0;
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// Position at the last key in the source that at or before target
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// The iterator is Valid() after this call iff the source contains
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// an entry that comes at or before target.
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virtual void SeekForPrev(const Slice& target) {}
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// Moves to the next entry in the source. After this call, Valid() is
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// true iff the iterator was not positioned at the last entry in the source.
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// REQUIRES: Valid()
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virtual void Next() = 0;
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// Moves to the previous entry in the source. After this call, Valid() is
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// true iff the iterator was not positioned at the first entry in source.
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// REQUIRES: Valid()
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virtual void Prev() = 0;
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// Return the key for the current entry. The underlying storage for
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// the returned slice is valid only until the next modification of
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// the iterator.
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// REQUIRES: Valid()
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virtual Slice key() const = 0;
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// Return the value for the current entry. The underlying storage for
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// the returned slice is valid only until the next modification of
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// the iterator.
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// REQUIRES: !AtEnd() && !AtStart()
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virtual Slice value() const = 0;
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// If an error has occurred, return it. Else return an ok status.
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// If non-blocking IO is requested and this operation cannot be
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// satisfied without doing some IO, then this returns Status::Incomplete().
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virtual Status status() const = 0;
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// Property "rocksdb.iterator.is-key-pinned":
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// If returning "1", this means that the Slice returned by key() is valid
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// as long as the iterator is not deleted.
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// It is guaranteed to always return "1" if
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// - Iterator created with ReadOptions::pin_data = true
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// - DB tables were created with
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// BlockBasedTableOptions::use_delta_encoding = false.
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// Property "rocksdb.iterator.super-version-number":
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// LSM version used by the iterator. The same format as DB Property
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// kCurrentSuperVersionNumber. See its comment for more information.
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virtual Status GetProperty(std::string prop_name, std::string* prop);
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private:
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// No copying allowed
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Iterator(const Iterator&);
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void operator=(const Iterator&);
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};
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// Return an empty iterator (yields nothing).
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extern Iterator* NewEmptyIterator();
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// Return an empty iterator with the specified status.
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extern Iterator* NewErrorIterator(const Status& status);
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} // namespace rocksdb
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#endif // STORAGE_ROCKSDB_INCLUDE_ITERATOR_H_
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