9fad3e21eb
Summary: When reseek happens in merging iterator, reseeking a child iterator can be avoided if: (1) the iterator represents imutable data (2) reseek() to a larger key than the current key (3) the current key of the child iterator is larger than the seek key because it is guaranteed that the result will fall into the same position. This optimization will be useful for use cases where users keep seeking to keys nearby in ascending order. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5286 Differential Revision: D15283635 Pulled By: siying fbshipit-source-id: 35f79ffd5ce3609146faa8cd55f2bfd733502f83
121 lines
3.3 KiB
C++
121 lines
3.3 KiB
C++
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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//
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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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#pragma once
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#include <set>
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#include "table/internal_iterator.h"
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namespace rocksdb {
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// A internal wrapper class with an interface similar to Iterator that caches
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// the valid() and key() results for an underlying iterator.
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// This can help avoid virtual function calls and also gives better
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// cache locality.
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template <class TValue = Slice>
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class IteratorWrapperBase {
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public:
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IteratorWrapperBase() : iter_(nullptr), valid_(false) {}
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explicit IteratorWrapperBase(InternalIteratorBase<TValue>* _iter)
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: iter_(nullptr) {
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Set(_iter);
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}
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~IteratorWrapperBase() {}
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InternalIteratorBase<TValue>* iter() const { return iter_; }
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// Set the underlying Iterator to _iter and return
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// previous underlying Iterator.
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InternalIteratorBase<TValue>* Set(InternalIteratorBase<TValue>* _iter) {
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InternalIteratorBase<TValue>* old_iter = iter_;
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iter_ = _iter;
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if (iter_ == nullptr) {
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valid_ = false;
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} else {
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Update();
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}
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return old_iter;
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}
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void DeleteIter(bool is_arena_mode) {
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if (iter_) {
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if (!is_arena_mode) {
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delete iter_;
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} else {
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iter_->~InternalIteratorBase<TValue>();
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}
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}
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}
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// Iterator interface methods
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bool Valid() const { return valid_; }
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Slice key() const { assert(Valid()); return key_; }
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TValue value() const {
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assert(Valid());
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return iter_->value();
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}
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// Methods below require iter() != nullptr
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Status status() const { assert(iter_); return iter_->status(); }
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void Next() {
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assert(iter_);
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valid_ = iter_->NextAndGetResult(&key_);
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assert(!valid_ || iter_->status().ok());
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}
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void Prev() { assert(iter_); iter_->Prev(); Update(); }
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void Seek(const Slice& k) {
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TEST_SYNC_POINT("IteratorWrapper::Seek:0");
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assert(iter_);
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iter_->Seek(k);
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Update();
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}
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void SeekForPrev(const Slice& k) {
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assert(iter_);
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iter_->SeekForPrev(k);
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Update();
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}
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void SeekToFirst() { assert(iter_); iter_->SeekToFirst(); Update(); }
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void SeekToLast() { assert(iter_); iter_->SeekToLast(); Update(); }
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void SetPinnedItersMgr(PinnedIteratorsManager* pinned_iters_mgr) {
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assert(iter_);
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iter_->SetPinnedItersMgr(pinned_iters_mgr);
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}
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bool IsKeyPinned() const {
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assert(Valid());
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return iter_->IsKeyPinned();
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}
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bool IsValuePinned() const {
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assert(Valid());
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return iter_->IsValuePinned();
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}
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private:
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void Update() {
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valid_ = iter_->Valid();
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if (valid_) {
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key_ = iter_->key();
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assert(iter_->status().ok());
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}
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}
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InternalIteratorBase<TValue>* iter_;
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bool valid_;
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Slice key_;
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};
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using IteratorWrapper = IteratorWrapperBase<Slice>;
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class Arena;
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// Return an empty iterator (yields nothing) allocated from arena.
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template <class TValue = Slice>
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extern InternalIteratorBase<TValue>* NewEmptyInternalIterator(Arena* arena);
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} // namespace rocksdb
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