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rocksdb/table/block_based/block_based_table_iterator.h

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// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
// This source code is licensed under both the GPLv2 (found in the
// COPYING file in the root directory) and Apache 2.0 License
// (found in the LICENSE.Apache file in the root 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.
#pragma once
#include "table/block_based/block_based_table_reader.h"
#include "table/block_based/block_based_table_reader_impl.h"
#include "table/block_based/block_prefetcher.h"
#include "table/block_based/reader_common.h"
namespace ROCKSDB_NAMESPACE {
// Iterates over the contents of BlockBasedTable.
class BlockBasedTableIterator : public InternalIteratorBase<Slice> {
// compaction_readahead_size: its value will only be used if for_compaction =
// true
// @param read_options Must outlive this iterator.
public:
BlockBasedTableIterator(
const BlockBasedTable* table, const ReadOptions& read_options,
const InternalKeyComparator& icomp,
std::unique_ptr<InternalIteratorBase<IndexValue>>&& index_iter,
bool check_filter, bool need_upper_bound_check,
const SliceTransform* prefix_extractor, TableReaderCaller caller,
size_t compaction_readahead_size = 0, bool allow_unprepared_value = false)
: index_iter_(std::move(index_iter)),
table_(table),
read_options_(read_options),
icomp_(icomp),
user_comparator_(icomp.user_comparator()),
pinned_iters_mgr_(nullptr),
prefix_extractor_(prefix_extractor),
lookup_context_(caller),
block_prefetcher_(
compaction_readahead_size,
table_->get_rep()->table_options.initial_auto_readahead_size),
allow_unprepared_value_(allow_unprepared_value),
block_iter_points_to_real_block_(false),
check_filter_(check_filter),
need_upper_bound_check_(need_upper_bound_check),
async_read_in_progress_(false) {}
~BlockBasedTableIterator() {}
void Seek(const Slice& target) override;
void SeekForPrev(const Slice& target) override;
void SeekToFirst() override;
void SeekToLast() override;
void Next() final override;
bool NextAndGetResult(IterateResult* result) override;
void Prev() override;
bool Valid() const override {
return !is_out_of_bound_ &&
(is_at_first_key_from_index_ ||
(block_iter_points_to_real_block_ && block_iter_.Valid()));
}
Slice key() const override {
assert(Valid());
if (is_at_first_key_from_index_) {
return index_iter_->value().first_internal_key;
} else {
return block_iter_.key();
}
}
Slice user_key() const override {
assert(Valid());
if (is_at_first_key_from_index_) {
return ExtractUserKey(index_iter_->value().first_internal_key);
} else {
return block_iter_.user_key();
}
}
bool PrepareValue() override {
assert(Valid());
if (!is_at_first_key_from_index_) {
return true;
}
return const_cast<BlockBasedTableIterator*>(this)
->MaterializeCurrentBlock();
}
Slice value() const override {
// PrepareValue() must have been called.
assert(!is_at_first_key_from_index_);
assert(Valid());
return block_iter_.value();
}
Status status() const override {
// Prefix index set status to NotFound when the prefix does not exist
if (!index_iter_->status().ok() && !index_iter_->status().IsNotFound()) {
return index_iter_->status();
} else if (block_iter_points_to_real_block_) {
return block_iter_.status();
} else if (async_read_in_progress_) {
return Status::TryAgain();
} else {
return Status::OK();
}
}
inline IterBoundCheck UpperBoundCheckResult() override {
if (is_out_of_bound_) {
return IterBoundCheck::kOutOfBound;
} else if (block_upper_bound_check_ ==
BlockUpperBound::kUpperBoundBeyondCurBlock) {
assert(!is_out_of_bound_);
return IterBoundCheck::kInbound;
} else {
return IterBoundCheck::kUnknown;
}
}
void SetPinnedItersMgr(PinnedIteratorsManager* pinned_iters_mgr) override {
pinned_iters_mgr_ = pinned_iters_mgr;
}
bool IsKeyPinned() const override {
// Our key comes either from block_iter_'s current key
// or index_iter_'s current *value*.
return pinned_iters_mgr_ && pinned_iters_mgr_->PinningEnabled() &&
((is_at_first_key_from_index_ && index_iter_->IsValuePinned()) ||
(block_iter_points_to_real_block_ && block_iter_.IsKeyPinned()));
}
bool IsValuePinned() const override {
assert(!is_at_first_key_from_index_);
assert(Valid());
// BlockIter::IsValuePinned() is always true. No need to check
return pinned_iters_mgr_ && pinned_iters_mgr_->PinningEnabled() &&
block_iter_points_to_real_block_;
}
void ResetDataIter() {
if (block_iter_points_to_real_block_) {
if (pinned_iters_mgr_ != nullptr && pinned_iters_mgr_->PinningEnabled()) {
block_iter_.DelegateCleanupsTo(pinned_iters_mgr_);
}
block_iter_.Invalidate(Status::OK());
block_iter_points_to_real_block_ = false;
}
block_upper_bound_check_ = BlockUpperBound::kUnknown;
}
void SavePrevIndexValue() {
if (block_iter_points_to_real_block_) {
// Reseek. If they end up with the same data block, we shouldn't re-fetch
// the same data block.
prev_block_offset_ = index_iter_->value().handle.offset();
}
}
void GetReadaheadState(ReadaheadFileInfo* readahead_file_info) override {
if (block_prefetcher_.prefetch_buffer() != nullptr &&
read_options_.adaptive_readahead) {
block_prefetcher_.prefetch_buffer()->GetReadaheadState(
&(readahead_file_info->data_block_readahead_info));
if (index_iter_) {
index_iter_->GetReadaheadState(readahead_file_info);
}
}
}
void SetReadaheadState(ReadaheadFileInfo* readahead_file_info) override {
if (read_options_.adaptive_readahead) {
block_prefetcher_.SetReadaheadState(
&(readahead_file_info->data_block_readahead_info));
if (index_iter_) {
index_iter_->SetReadaheadState(readahead_file_info);
}
}
}
std::unique_ptr<InternalIteratorBase<IndexValue>> index_iter_;
private:
enum class IterDirection {
kForward,
kBackward,
};
// This enum indicates whether the upper bound falls into current block
// or beyond.
// +-------------+
// | cur block | <-- (1)
// +-------------+
// <-- (2)
// --- <boundary key> ---
// <-- (3)
// +-------------+
// | next block | <-- (4)
// ......
//
// When the block is smaller than <boundary key>, kUpperBoundInCurBlock
// is the value to use. The examples are (1) or (2) in the graph. It means
// all keys in the next block or beyond will be out of bound. Keys within
// the current block may or may not be out of bound.
// When the block is larger or equal to <boundary key>,
// kUpperBoundBeyondCurBlock is to be used. The examples are (3) and (4)
// in the graph. It means that all keys in the current block is within the
// upper bound and keys in the next block may or may not be within the uppder
// bound.
// If the boundary key hasn't been checked against the upper bound,
// kUnknown can be used.
enum class BlockUpperBound {
kUpperBoundInCurBlock,
kUpperBoundBeyondCurBlock,
kUnknown,
};
const BlockBasedTable* table_;
const ReadOptions& read_options_;
const InternalKeyComparator& icomp_;
UserComparatorWrapper user_comparator_;
PinnedIteratorsManager* pinned_iters_mgr_;
DataBlockIter block_iter_;
const SliceTransform* prefix_extractor_;
uint64_t prev_block_offset_ = std::numeric_limits<uint64_t>::max();
BlockCacheLookupContext lookup_context_;
BlockPrefetcher block_prefetcher_;
const bool allow_unprepared_value_;
// True if block_iter_ is initialized and points to the same block
// as index iterator.
bool block_iter_points_to_real_block_;
// See InternalIteratorBase::IsOutOfBound().
bool is_out_of_bound_ = false;
// How current data block's boundary key with the next block is compared with
// iterate upper bound.
BlockUpperBound block_upper_bound_check_ = BlockUpperBound::kUnknown;
// True if we're standing at the first key of a block, and we haven't loaded
// that block yet. A call to PrepareValue() will trigger loading the block.
bool is_at_first_key_from_index_ = false;
bool check_filter_;
// TODO(Zhongyi): pick a better name
bool need_upper_bound_check_;
bool async_read_in_progress_;
// If `target` is null, seek to first.
void SeekImpl(const Slice* target, bool async_prefetch);
void InitDataBlock();
void AsyncInitDataBlock(bool is_first_pass);
bool MaterializeCurrentBlock();
void FindKeyForward();
void FindBlockForward();
void FindKeyBackward();
void CheckOutOfBound();
// Check if data block is fully within iterate_upper_bound.
//
// Note MyRocks may update iterate bounds between seek. To workaround it,
// we need to check and update data_block_within_upper_bound_ accordingly.
void CheckDataBlockWithinUpperBound();
bool CheckPrefixMayMatch(const Slice& ikey, IterDirection direction) {
if (need_upper_bound_check_ && direction == IterDirection::kBackward) {
// Upper bound check isn't sufficient for backward direction to
// guarantee the same result as total order, so disable prefix
// check.
return true;
}
if (check_filter_ && !table_->PrefixRangeMayMatch(
ikey, read_options_, prefix_extractor_,
need_upper_bound_check_, &lookup_context_)) {
// TODO remember the iterator is invalidated because of prefix
// match. This can avoid the upper level file iterator to falsely
// believe the position is the end of the SST file and move to
// the first key of the next file.
ResetDataIter();
return false;
}
return true;
}
};
} // namespace ROCKSDB_NAMESPACE