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rocksdb/db/tailing_iter.cc

175 lines
4.6 KiB

// Copyright (c) 2013, 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.
#include "db/tailing_iter.h"
#include <string>
#include <utility>
#include "db/db_impl.h"
#include "rocksdb/slice.h"
#include "rocksdb/slice_transform.h"
namespace rocksdb {
TailingIterator::TailingIterator(DBImpl* db, const ReadOptions& options,
const Comparator* comparator)
: db_(db), options_(options), comparator_(comparator),
version_number_(0), current_(nullptr),
status_(Status::InvalidArgument("Seek() not called on this iterator")) {}
bool TailingIterator::Valid() const {
return current_ != nullptr;
}
void TailingIterator::SeekToFirst() {
if (!IsCurrentVersion()) {
CreateIterators();
}
mutable_->SeekToFirst();
immutable_->SeekToFirst();
UpdateCurrent();
}
void TailingIterator::Seek(const Slice& target) {
if (!IsCurrentVersion()) {
CreateIterators();
}
mutable_->Seek(target);
// We maintain the interval (prev_key_, immutable_->key()] such that there
// are no records with keys within that range in immutable_ other than
// immutable_->key(). Since immutable_ can't change in this version, we don't
// need to do a seek if 'target' belongs to that interval (i.e. immutable_ is
// already at the correct position)!
//
// If options.prefix_seek is used and immutable_ is not valid, seek if target
// has a different prefix than prev_key.
//
// prev_key_ is updated by Next(). SeekImmutable() sets prev_key_ to
// 'target' -- in this case, prev_key_ is included in the interval, so
// prev_inclusive_ has to be set.
if (!is_prev_set_ ||
comparator_->Compare(prev_key_, target) >= !is_prev_inclusive_ ||
(immutable_->Valid() &&
comparator_->Compare(target, immutable_->key()) > 0) ||
(options_.prefix_seek && !IsSamePrefix(target))) {
SeekImmutable(target);
}
UpdateCurrent();
}
void TailingIterator::Next() {
assert(Valid());
if (!IsCurrentVersion()) {
// save the current key, create new iterators and then seek
std::string current_key = key().ToString();
Slice key_slice(current_key.data(), current_key.size());
CreateIterators();
Seek(key_slice);
if (!Valid() || key().compare(key_slice) != 0) {
// record with current_key no longer exists
return;
}
} else if (current_ == immutable_.get()) {
// immutable iterator is advanced -- update prev_key_
prev_key_ = key().ToString();
is_prev_inclusive_ = false;
is_prev_set_ = true;
}
current_->Next();
UpdateCurrent();
}
Slice TailingIterator::key() const {
assert(Valid());
return current_->key();
}
Slice TailingIterator::value() const {
assert(Valid());
return current_->value();
}
Status TailingIterator::status() const {
if (!status_.ok()) {
return status_;
} else if (!mutable_->status().ok()) {
return mutable_->status();
} else {
return immutable_->status();
}
}
void TailingIterator::Prev() {
status_ = Status::NotSupported("This iterator doesn't support Prev()");
}
void TailingIterator::SeekToLast() {
status_ = Status::NotSupported("This iterator doesn't support SeekToLast()");
}
void TailingIterator::CreateIterators() {
std::pair<Iterator*, Iterator*> iters =
db_->GetTailingIteratorPair(options_, &version_number_);
assert(iters.first && iters.second);
mutable_.reset(iters.first);
immutable_.reset(iters.second);
current_ = nullptr;
is_prev_set_ = false;
}
void TailingIterator::UpdateCurrent() {
current_ = nullptr;
if (mutable_->Valid()) {
current_ = mutable_.get();
}
if (immutable_->Valid() &&
(current_ == nullptr ||
comparator_->Compare(immutable_->key(), current_->key()) < 0)) {
current_ = immutable_.get();
}
if (!status_.ok()) {
// reset status that was set by Prev() or SeekToLast()
status_ = Status::OK();
}
}
bool TailingIterator::IsCurrentVersion() const {
return mutable_ != nullptr && immutable_ != nullptr &&
version_number_ == db_->CurrentVersionNumber();
}
bool TailingIterator::IsSamePrefix(const Slice& target) const {
const SliceTransform* extractor = db_->options_.prefix_extractor.get();
assert(extractor);
assert(is_prev_set_);
return extractor->Transform(target)
.compare(extractor->Transform(prev_key_)) == 0;
}
void TailingIterator::SeekImmutable(const Slice& target) {
prev_key_ = target.ToString();
is_prev_inclusive_ = true;
is_prev_set_ = true;
immutable_->Seek(target);
}
} // namespace rocksdb