fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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251 lines
9.0 KiB
251 lines
9.0 KiB
// 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 "table/block_based/block_based_table_reader.h"
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#include "table/block_based/block_based_table_reader_impl.h"
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#include "table/block_based/block_prefetcher.h"
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#include "table/block_based/reader_common.h"
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namespace ROCKSDB_NAMESPACE {
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// Iterates over the contents of BlockBasedTable.
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class BlockBasedTableIterator : public InternalIteratorBase<Slice> {
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// compaction_readahead_size: its value will only be used if for_compaction =
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// true
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// @param read_options Must outlive this iterator.
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public:
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BlockBasedTableIterator(
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const BlockBasedTable* table, const ReadOptions& read_options,
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const InternalKeyComparator& icomp,
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std::unique_ptr<InternalIteratorBase<IndexValue>>&& index_iter,
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bool check_filter, bool need_upper_bound_check,
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const SliceTransform* prefix_extractor, TableReaderCaller caller,
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size_t compaction_readahead_size = 0, bool allow_unprepared_value = false)
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: table_(table),
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read_options_(read_options),
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icomp_(icomp),
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user_comparator_(icomp.user_comparator()),
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index_iter_(std::move(index_iter)),
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pinned_iters_mgr_(nullptr),
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prefix_extractor_(prefix_extractor),
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lookup_context_(caller),
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block_prefetcher_(compaction_readahead_size),
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allow_unprepared_value_(allow_unprepared_value),
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block_iter_points_to_real_block_(false),
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check_filter_(check_filter),
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need_upper_bound_check_(need_upper_bound_check) {}
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~BlockBasedTableIterator() {}
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void Seek(const Slice& target) override;
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void SeekForPrev(const Slice& target) override;
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void SeekToFirst() override;
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void SeekToLast() override;
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void Next() final override;
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bool NextAndGetResult(IterateResult* result) override;
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void Prev() override;
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bool Valid() const override {
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return !is_out_of_bound_ &&
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(is_at_first_key_from_index_ ||
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(block_iter_points_to_real_block_ && block_iter_.Valid()));
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}
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Slice key() const override {
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assert(Valid());
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if (is_at_first_key_from_index_) {
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return index_iter_->value().first_internal_key;
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} else {
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return block_iter_.key();
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}
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}
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Slice user_key() const override {
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assert(Valid());
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if (is_at_first_key_from_index_) {
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return ExtractUserKey(index_iter_->value().first_internal_key);
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} else {
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return block_iter_.user_key();
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}
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}
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bool PrepareValue() override {
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assert(Valid());
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if (!is_at_first_key_from_index_) {
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return true;
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}
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return const_cast<BlockBasedTableIterator*>(this)
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->MaterializeCurrentBlock();
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}
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Slice value() const override {
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// PrepareValue() must have been called.
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assert(!is_at_first_key_from_index_);
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assert(Valid());
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return block_iter_.value();
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}
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Status status() const override {
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// Prefix index set status to NotFound when the prefix does not exist
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if (!index_iter_->status().ok() && !index_iter_->status().IsNotFound()) {
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return index_iter_->status();
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} else if (block_iter_points_to_real_block_) {
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return block_iter_.status();
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} else {
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return Status::OK();
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}
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}
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inline IterBoundCheck UpperBoundCheckResult() override {
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if (is_out_of_bound_) {
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return IterBoundCheck::kOutOfBound;
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} else if (block_upper_bound_check_ ==
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BlockUpperBound::kUpperBoundBeyondCurBlock) {
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assert(!is_out_of_bound_);
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return IterBoundCheck::kInbound;
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} else {
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return IterBoundCheck::kUnknown;
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}
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}
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void SetPinnedItersMgr(PinnedIteratorsManager* pinned_iters_mgr) override {
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pinned_iters_mgr_ = pinned_iters_mgr;
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}
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bool IsKeyPinned() const override {
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// Our key comes either from block_iter_'s current key
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// or index_iter_'s current *value*.
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return pinned_iters_mgr_ && pinned_iters_mgr_->PinningEnabled() &&
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((is_at_first_key_from_index_ && index_iter_->IsValuePinned()) ||
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(block_iter_points_to_real_block_ && block_iter_.IsKeyPinned()));
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}
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bool IsValuePinned() const override {
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assert(!is_at_first_key_from_index_);
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assert(Valid());
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// BlockIter::IsValuePinned() is always true. No need to check
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return pinned_iters_mgr_ && pinned_iters_mgr_->PinningEnabled() &&
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block_iter_points_to_real_block_;
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}
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void ResetDataIter() {
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if (block_iter_points_to_real_block_) {
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if (pinned_iters_mgr_ != nullptr && pinned_iters_mgr_->PinningEnabled()) {
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block_iter_.DelegateCleanupsTo(pinned_iters_mgr_);
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}
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block_iter_.Invalidate(Status::OK());
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block_iter_points_to_real_block_ = false;
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}
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block_upper_bound_check_ = BlockUpperBound::kUnknown;
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}
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void SavePrevIndexValue() {
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if (block_iter_points_to_real_block_) {
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// Reseek. If they end up with the same data block, we shouldn't re-fetch
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// the same data block.
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prev_block_offset_ = index_iter_->value().handle.offset();
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}
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}
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private:
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enum class IterDirection {
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kForward,
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kBackward,
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};
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// This enum indicates whether the upper bound falls into current block
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// or beyond.
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// +-------------+
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// | cur block | <-- (1)
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// +-------------+
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// <-- (2)
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// --- <boundary key> ---
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// <-- (3)
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// +-------------+
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// | next block | <-- (4)
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// ......
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//
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// When the block is smaller than <boundary key>, kUpperBoundInCurBlock
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// is the value to use. The examples are (1) or (2) in the graph. It means
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// all keys in the next block or beyond will be out of bound. Keys within
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// the current block may or may not be out of bound.
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// When the block is larger or equal to <boundary key>,
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// kUpperBoundBeyondCurBlock is to be used. The examples are (3) and (4)
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// in the graph. It means that all keys in the current block is within the
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// upper bound and keys in the next block may or may not be within the uppder
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// bound.
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// If the boundary key hasn't been checked against the upper bound,
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// kUnknown can be used.
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enum class BlockUpperBound {
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kUpperBoundInCurBlock,
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kUpperBoundBeyondCurBlock,
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kUnknown,
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};
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const BlockBasedTable* table_;
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const ReadOptions& read_options_;
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const InternalKeyComparator& icomp_;
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UserComparatorWrapper user_comparator_;
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std::unique_ptr<InternalIteratorBase<IndexValue>> index_iter_;
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PinnedIteratorsManager* pinned_iters_mgr_;
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DataBlockIter block_iter_;
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const SliceTransform* prefix_extractor_;
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uint64_t prev_block_offset_ = std::numeric_limits<uint64_t>::max();
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BlockCacheLookupContext lookup_context_;
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BlockPrefetcher block_prefetcher_;
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const bool allow_unprepared_value_;
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// True if block_iter_ is initialized and points to the same block
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// as index iterator.
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bool block_iter_points_to_real_block_;
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// See InternalIteratorBase::IsOutOfBound().
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bool is_out_of_bound_ = false;
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// How current data block's boundary key with the next block is compared with
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// iterate upper bound.
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BlockUpperBound block_upper_bound_check_ = BlockUpperBound::kUnknown;
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// True if we're standing at the first key of a block, and we haven't loaded
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// that block yet. A call to PrepareValue() will trigger loading the block.
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bool is_at_first_key_from_index_ = false;
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bool check_filter_;
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// TODO(Zhongyi): pick a better name
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bool need_upper_bound_check_;
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// If `target` is null, seek to first.
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void SeekImpl(const Slice* target);
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void InitDataBlock();
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bool MaterializeCurrentBlock();
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void FindKeyForward();
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void FindBlockForward();
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void FindKeyBackward();
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void CheckOutOfBound();
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// Check if data block is fully within iterate_upper_bound.
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//
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// Note MyRocks may update iterate bounds between seek. To workaround it,
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// we need to check and update data_block_within_upper_bound_ accordingly.
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void CheckDataBlockWithinUpperBound();
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bool CheckPrefixMayMatch(const Slice& ikey, IterDirection direction) {
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if (need_upper_bound_check_ && direction == IterDirection::kBackward) {
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// Upper bound check isn't sufficient for backward direction to
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// guarantee the same result as total order, so disable prefix
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// check.
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return true;
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}
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if (check_filter_ &&
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!table_->PrefixMayMatch(ikey, read_options_, prefix_extractor_,
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need_upper_bound_check_, &lookup_context_)) {
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// TODO remember the iterator is invalidated because of prefix
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// match. This can avoid the upper level file iterator to falsely
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// believe the position is the end of the SST file and move to
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// the first key of the next file.
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ResetDataIter();
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return false;
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}
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return true;
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}
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};
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} // namespace ROCKSDB_NAMESPACE
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