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Diffstat (limited to 'src/rocksdb/db/db_iter.cc')
| -rw-r--r-- | src/rocksdb/db/db_iter.cc | 1708 |
1 files changed, 1708 insertions, 0 deletions
diff --git a/src/rocksdb/db/db_iter.cc b/src/rocksdb/db/db_iter.cc new file mode 100644 index 000000000..e1375deb7 --- /dev/null +++ b/src/rocksdb/db/db_iter.cc @@ -0,0 +1,1708 @@ +// 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. + +#include "db/db_iter.h" + +#include <iostream> +#include <limits> +#include <string> + +#include "db/dbformat.h" +#include "db/merge_context.h" +#include "db/merge_helper.h" +#include "db/pinned_iterators_manager.h" +#include "db/wide/wide_column_serialization.h" +#include "file/filename.h" +#include "logging/logging.h" +#include "memory/arena.h" +#include "monitoring/perf_context_imp.h" +#include "rocksdb/env.h" +#include "rocksdb/iterator.h" +#include "rocksdb/merge_operator.h" +#include "rocksdb/options.h" +#include "rocksdb/system_clock.h" +#include "table/internal_iterator.h" +#include "table/iterator_wrapper.h" +#include "trace_replay/trace_replay.h" +#include "util/mutexlock.h" +#include "util/string_util.h" +#include "util/user_comparator_wrapper.h" + +namespace ROCKSDB_NAMESPACE { + +DBIter::DBIter(Env* _env, const ReadOptions& read_options, + const ImmutableOptions& ioptions, + const MutableCFOptions& mutable_cf_options, + const Comparator* cmp, InternalIterator* iter, + const Version* version, SequenceNumber s, bool arena_mode, + uint64_t max_sequential_skip_in_iterations, + ReadCallback* read_callback, DBImpl* db_impl, + ColumnFamilyData* cfd, bool expose_blob_index) + : prefix_extractor_(mutable_cf_options.prefix_extractor.get()), + env_(_env), + clock_(ioptions.clock), + logger_(ioptions.logger), + user_comparator_(cmp), + merge_operator_(ioptions.merge_operator.get()), + iter_(iter), + version_(version), + read_callback_(read_callback), + sequence_(s), + statistics_(ioptions.stats), + max_skip_(max_sequential_skip_in_iterations), + max_skippable_internal_keys_(read_options.max_skippable_internal_keys), + num_internal_keys_skipped_(0), + iterate_lower_bound_(read_options.iterate_lower_bound), + iterate_upper_bound_(read_options.iterate_upper_bound), + direction_(kForward), + valid_(false), + current_entry_is_merged_(false), + is_key_seqnum_zero_(false), + prefix_same_as_start_(mutable_cf_options.prefix_extractor + ? read_options.prefix_same_as_start + : false), + pin_thru_lifetime_(read_options.pin_data), + expect_total_order_inner_iter_(prefix_extractor_ == nullptr || + read_options.total_order_seek || + read_options.auto_prefix_mode), + read_tier_(read_options.read_tier), + fill_cache_(read_options.fill_cache), + verify_checksums_(read_options.verify_checksums), + expose_blob_index_(expose_blob_index), + is_blob_(false), + arena_mode_(arena_mode), + db_impl_(db_impl), + cfd_(cfd), + timestamp_ub_(read_options.timestamp), + timestamp_lb_(read_options.iter_start_ts), + timestamp_size_(timestamp_ub_ ? timestamp_ub_->size() : 0) { + RecordTick(statistics_, NO_ITERATOR_CREATED); + if (pin_thru_lifetime_) { + pinned_iters_mgr_.StartPinning(); + } + if (iter_.iter()) { + iter_.iter()->SetPinnedItersMgr(&pinned_iters_mgr_); + } + status_.PermitUncheckedError(); + assert(timestamp_size_ == + user_comparator_.user_comparator()->timestamp_size()); +} + +Status DBIter::GetProperty(std::string prop_name, std::string* prop) { + if (prop == nullptr) { + return Status::InvalidArgument("prop is nullptr"); + } + if (prop_name == "rocksdb.iterator.super-version-number") { + // First try to pass the value returned from inner iterator. + return iter_.iter()->GetProperty(prop_name, prop); + } else if (prop_name == "rocksdb.iterator.is-key-pinned") { + if (valid_) { + *prop = (pin_thru_lifetime_ && saved_key_.IsKeyPinned()) ? "1" : "0"; + } else { + *prop = "Iterator is not valid."; + } + return Status::OK(); + } else if (prop_name == "rocksdb.iterator.internal-key") { + *prop = saved_key_.GetUserKey().ToString(); + return Status::OK(); + } + return Status::InvalidArgument("Unidentified property."); +} + +bool DBIter::ParseKey(ParsedInternalKey* ikey) { + Status s = ParseInternalKey(iter_.key(), ikey, false /* log_err_key */); + if (!s.ok()) { + status_ = Status::Corruption("In DBIter: ", s.getState()); + valid_ = false; + ROCKS_LOG_ERROR(logger_, "In DBIter: %s", status_.getState()); + return false; + } else { + return true; + } +} + +void DBIter::Next() { + assert(valid_); + assert(status_.ok()); + + PERF_CPU_TIMER_GUARD(iter_next_cpu_nanos, clock_); + // Release temporarily pinned blocks from last operation + ReleaseTempPinnedData(); + ResetBlobValue(); + ResetValueAndColumns(); + local_stats_.skip_count_ += num_internal_keys_skipped_; + local_stats_.skip_count_--; + num_internal_keys_skipped_ = 0; + bool ok = true; + if (direction_ == kReverse) { + is_key_seqnum_zero_ = false; + if (!ReverseToForward()) { + ok = false; + } + } else if (!current_entry_is_merged_) { + // If the current value is not a merge, the iter position is the + // current key, which is already returned. We can safely issue a + // Next() without checking the current key. + // If the current key is a merge, very likely iter already points + // to the next internal position. + assert(iter_.Valid()); + iter_.Next(); + PERF_COUNTER_ADD(internal_key_skipped_count, 1); + } + + local_stats_.next_count_++; + if (ok && iter_.Valid()) { + ClearSavedValue(); + + if (prefix_same_as_start_) { + assert(prefix_extractor_ != nullptr); + const Slice prefix = prefix_.GetUserKey(); + FindNextUserEntry(true /* skipping the current user key */, &prefix); + } else { + FindNextUserEntry(true /* skipping the current user key */, nullptr); + } + } else { + is_key_seqnum_zero_ = false; + valid_ = false; + } + if (statistics_ != nullptr && valid_) { + local_stats_.next_found_count_++; + local_stats_.bytes_read_ += (key().size() + value().size()); + } +} + +bool DBIter::SetBlobValueIfNeeded(const Slice& user_key, + const Slice& blob_index) { + assert(!is_blob_); + assert(blob_value_.empty()); + + if (expose_blob_index_) { // Stacked BlobDB implementation + is_blob_ = true; + return true; + } + + if (!version_) { + status_ = Status::Corruption("Encountered unexpected blob index."); + valid_ = false; + return false; + } + + // TODO: consider moving ReadOptions from ArenaWrappedDBIter to DBIter to + // avoid having to copy options back and forth. + ReadOptions read_options; + read_options.read_tier = read_tier_; + read_options.fill_cache = fill_cache_; + read_options.verify_checksums = verify_checksums_; + + constexpr FilePrefetchBuffer* prefetch_buffer = nullptr; + constexpr uint64_t* bytes_read = nullptr; + + const Status s = version_->GetBlob(read_options, user_key, blob_index, + prefetch_buffer, &blob_value_, bytes_read); + + if (!s.ok()) { + status_ = s; + valid_ = false; + return false; + } + + is_blob_ = true; + return true; +} + +bool DBIter::SetValueAndColumnsFromEntity(Slice slice) { + assert(value_.empty()); + assert(wide_columns_.empty()); + + const Status s = WideColumnSerialization::Deserialize(slice, wide_columns_); + + if (!s.ok()) { + status_ = s; + valid_ = false; + return false; + } + + if (!wide_columns_.empty() && + wide_columns_[0].name() == kDefaultWideColumnName) { + value_ = wide_columns_[0].value(); + } + + return true; +} + +// PRE: saved_key_ has the current user key if skipping_saved_key +// POST: saved_key_ should have the next user key if valid_, +// if the current entry is a result of merge +// current_entry_is_merged_ => true +// saved_value_ => the merged value +// +// NOTE: In between, saved_key_ can point to a user key that has +// a delete marker or a sequence number higher than sequence_ +// saved_key_ MUST have a proper user_key before calling this function +// +// The prefix parameter, if not null, indicates that we need to iterate +// within the prefix, and the iterator needs to be made invalid, if no +// more entry for the prefix can be found. +bool DBIter::FindNextUserEntry(bool skipping_saved_key, const Slice* prefix) { + PERF_TIMER_GUARD(find_next_user_entry_time); + return FindNextUserEntryInternal(skipping_saved_key, prefix); +} + +// Actual implementation of DBIter::FindNextUserEntry() +bool DBIter::FindNextUserEntryInternal(bool skipping_saved_key, + const Slice* prefix) { + // Loop until we hit an acceptable entry to yield + assert(iter_.Valid()); + assert(status_.ok()); + assert(direction_ == kForward); + current_entry_is_merged_ = false; + + // How many times in a row we have skipped an entry with user key less than + // or equal to saved_key_. We could skip these entries either because + // sequence numbers were too high or because skipping_saved_key = true. + // What saved_key_ contains throughout this method: + // - if skipping_saved_key : saved_key_ contains the key that we need + // to skip, and we haven't seen any keys greater + // than that, + // - if num_skipped > 0 : saved_key_ contains the key that we have skipped + // num_skipped times, and we haven't seen any keys + // greater than that, + // - none of the above : saved_key_ can contain anything, it doesn't + // matter. + uint64_t num_skipped = 0; + // For write unprepared, the target sequence number in reseek could be larger + // than the snapshot, and thus needs to be skipped again. This could result in + // an infinite loop of reseeks. To avoid that, we limit the number of reseeks + // to one. + bool reseek_done = false; + + do { + // Will update is_key_seqnum_zero_ as soon as we parsed the current key + // but we need to save the previous value to be used in the loop. + bool is_prev_key_seqnum_zero = is_key_seqnum_zero_; + if (!ParseKey(&ikey_)) { + is_key_seqnum_zero_ = false; + return false; + } + Slice user_key_without_ts = + StripTimestampFromUserKey(ikey_.user_key, timestamp_size_); + + is_key_seqnum_zero_ = (ikey_.sequence == 0); + + assert(iterate_upper_bound_ == nullptr || + iter_.UpperBoundCheckResult() != IterBoundCheck::kInbound || + user_comparator_.CompareWithoutTimestamp( + user_key_without_ts, /*a_has_ts=*/false, *iterate_upper_bound_, + /*b_has_ts=*/false) < 0); + if (iterate_upper_bound_ != nullptr && + iter_.UpperBoundCheckResult() != IterBoundCheck::kInbound && + user_comparator_.CompareWithoutTimestamp( + user_key_without_ts, /*a_has_ts=*/false, *iterate_upper_bound_, + /*b_has_ts=*/false) >= 0) { + break; + } + + assert(prefix == nullptr || prefix_extractor_ != nullptr); + if (prefix != nullptr && + prefix_extractor_->Transform(user_key_without_ts).compare(*prefix) != + 0) { + assert(prefix_same_as_start_); + break; + } + + if (TooManyInternalKeysSkipped()) { + return false; + } + + assert(ikey_.user_key.size() >= timestamp_size_); + Slice ts = timestamp_size_ > 0 ? ExtractTimestampFromUserKey( + ikey_.user_key, timestamp_size_) + : Slice(); + bool more_recent = false; + if (IsVisible(ikey_.sequence, ts, &more_recent)) { + // If the previous entry is of seqnum 0, the current entry will not + // possibly be skipped. This condition can potentially be relaxed to + // prev_key.seq <= ikey_.sequence. We are cautious because it will be more + // prone to bugs causing the same user key with the same sequence number. + // Note that with current timestamp implementation, the same user key can + // have different timestamps and zero sequence number on the bottommost + // level. This may change in the future. + if ((!is_prev_key_seqnum_zero || timestamp_size_ > 0) && + skipping_saved_key && + CompareKeyForSkip(ikey_.user_key, saved_key_.GetUserKey()) <= 0) { + num_skipped++; // skip this entry + PERF_COUNTER_ADD(internal_key_skipped_count, 1); + } else { + assert(!skipping_saved_key || + CompareKeyForSkip(ikey_.user_key, saved_key_.GetUserKey()) > 0); + if (!iter_.PrepareValue()) { + assert(!iter_.status().ok()); + valid_ = false; + return false; + } + num_skipped = 0; + reseek_done = false; + switch (ikey_.type) { + case kTypeDeletion: + case kTypeDeletionWithTimestamp: + case kTypeSingleDeletion: + // Arrange to skip all upcoming entries for this key since + // they are hidden by this deletion. + if (timestamp_lb_) { + saved_key_.SetInternalKey(ikey_); + valid_ = true; + return true; + } else { + saved_key_.SetUserKey( + ikey_.user_key, !pin_thru_lifetime_ || + !iter_.iter()->IsKeyPinned() /* copy */); + skipping_saved_key = true; + PERF_COUNTER_ADD(internal_delete_skipped_count, 1); + } + break; + case kTypeValue: + case kTypeBlobIndex: + case kTypeWideColumnEntity: + if (timestamp_lb_) { + saved_key_.SetInternalKey(ikey_); + } else { + saved_key_.SetUserKey( + ikey_.user_key, !pin_thru_lifetime_ || + !iter_.iter()->IsKeyPinned() /* copy */); + } + + if (ikey_.type == kTypeBlobIndex) { + if (!SetBlobValueIfNeeded(ikey_.user_key, iter_.value())) { + return false; + } + + SetValueAndColumnsFromPlain(expose_blob_index_ ? iter_.value() + : blob_value_); + } else if (ikey_.type == kTypeWideColumnEntity) { + if (!SetValueAndColumnsFromEntity(iter_.value())) { + return false; + } + } else { + assert(ikey_.type == kTypeValue); + SetValueAndColumnsFromPlain(iter_.value()); + } + + valid_ = true; + return true; + break; + case kTypeMerge: + saved_key_.SetUserKey( + ikey_.user_key, + !pin_thru_lifetime_ || !iter_.iter()->IsKeyPinned() /* copy */); + // By now, we are sure the current ikey is going to yield a value + current_entry_is_merged_ = true; + valid_ = true; + return MergeValuesNewToOld(); // Go to a different state machine + break; + default: + valid_ = false; + status_ = Status::Corruption( + "Unknown value type: " + + std::to_string(static_cast<unsigned int>(ikey_.type))); + return false; + } + } + } else { + if (more_recent) { + PERF_COUNTER_ADD(internal_recent_skipped_count, 1); + } + + // This key was inserted after our snapshot was taken or skipped by + // timestamp range. If this happens too many times in a row for the same + // user key, we want to seek to the target sequence number. + int cmp = user_comparator_.CompareWithoutTimestamp( + ikey_.user_key, saved_key_.GetUserKey()); + if (cmp == 0 || (skipping_saved_key && cmp < 0)) { + num_skipped++; + } else { + saved_key_.SetUserKey( + ikey_.user_key, + !iter_.iter()->IsKeyPinned() || !pin_thru_lifetime_ /* copy */); + skipping_saved_key = false; + num_skipped = 0; + reseek_done = false; + } + } + + // If we have sequentially iterated via numerous equal keys, then it's + // better to seek so that we can avoid too many key comparisons. + // + // To avoid infinite loops, do not reseek if we have already attempted to + // reseek previously. + // + // TODO(lth): If we reseek to sequence number greater than ikey_.sequence, + // then it does not make sense to reseek as we would actually land further + // away from the desired key. There is opportunity for optimization here. + if (num_skipped > max_skip_ && !reseek_done) { + is_key_seqnum_zero_ = false; + num_skipped = 0; + reseek_done = true; + std::string last_key; + if (skipping_saved_key) { + // We're looking for the next user-key but all we see are the same + // user-key with decreasing sequence numbers. Fast forward to + // sequence number 0 and type deletion (the smallest type). + if (timestamp_size_ == 0) { + AppendInternalKey( + &last_key, + ParsedInternalKey(saved_key_.GetUserKey(), 0, kTypeDeletion)); + } else { + const std::string kTsMin(timestamp_size_, '\0'); + AppendInternalKeyWithDifferentTimestamp( + &last_key, + ParsedInternalKey(saved_key_.GetUserKey(), 0, kTypeDeletion), + kTsMin); + } + // Don't set skipping_saved_key = false because we may still see more + // user-keys equal to saved_key_. + } else { + // We saw multiple entries with this user key and sequence numbers + // higher than sequence_. Fast forward to sequence_. + // Note that this only covers a case when a higher key was overwritten + // many times since our snapshot was taken, not the case when a lot of + // different keys were inserted after our snapshot was taken. + if (timestamp_size_ == 0) { + AppendInternalKey( + &last_key, ParsedInternalKey(saved_key_.GetUserKey(), sequence_, + kValueTypeForSeek)); + } else { + AppendInternalKeyWithDifferentTimestamp( + &last_key, + ParsedInternalKey(saved_key_.GetUserKey(), sequence_, + kValueTypeForSeek), + *timestamp_ub_); + } + } + iter_.Seek(last_key); + RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION); + } else { + iter_.Next(); + } + } while (iter_.Valid()); + + valid_ = false; + return iter_.status().ok(); +} + +// Merge values of the same user key starting from the current iter_ position +// Scan from the newer entries to older entries. +// PRE: iter_.key() points to the first merge type entry +// saved_key_ stores the user key +// iter_.PrepareValue() has been called +// POST: saved_value_ has the merged value for the user key +// iter_ points to the next entry (or invalid) +bool DBIter::MergeValuesNewToOld() { + if (!merge_operator_) { + ROCKS_LOG_ERROR(logger_, "Options::merge_operator is null."); + status_ = Status::InvalidArgument("merge_operator_ must be set."); + valid_ = false; + return false; + } + + // Temporarily pin the blocks that hold merge operands + TempPinData(); + merge_context_.Clear(); + // Start the merge process by pushing the first operand + merge_context_.PushOperand( + iter_.value(), iter_.iter()->IsValuePinned() /* operand_pinned */); + TEST_SYNC_POINT("DBIter::MergeValuesNewToOld:PushedFirstOperand"); + + ParsedInternalKey ikey; + for (iter_.Next(); iter_.Valid(); iter_.Next()) { + TEST_SYNC_POINT("DBIter::MergeValuesNewToOld:SteppedToNextOperand"); + if (!ParseKey(&ikey)) { + return false; + } + + if (!user_comparator_.EqualWithoutTimestamp(ikey.user_key, + saved_key_.GetUserKey())) { + // hit the next user key, stop right here + break; + } + if (kTypeDeletion == ikey.type || kTypeSingleDeletion == ikey.type || + kTypeDeletionWithTimestamp == ikey.type) { + // hit a delete with the same user key, stop right here + // iter_ is positioned after delete + iter_.Next(); + break; + } + if (!iter_.PrepareValue()) { + valid_ = false; + return false; + } + + if (kTypeValue == ikey.type) { + // hit a put, merge the put value with operands and store the + // final result in saved_value_. We are done! + const Slice val = iter_.value(); + if (!Merge(&val, ikey.user_key)) { + return false; + } + // iter_ is positioned after put + iter_.Next(); + if (!iter_.status().ok()) { + valid_ = false; + return false; + } + return true; + } else if (kTypeMerge == ikey.type) { + // hit a merge, add the value as an operand and run associative merge. + // when complete, add result to operands and continue. + merge_context_.PushOperand( + iter_.value(), iter_.iter()->IsValuePinned() /* operand_pinned */); + PERF_COUNTER_ADD(internal_merge_count, 1); + } else if (kTypeBlobIndex == ikey.type) { + if (expose_blob_index_) { + status_ = + Status::NotSupported("BlobDB does not support merge operator."); + valid_ = false; + return false; + } + // hit a put, merge the put value with operands and store the + // final result in saved_value_. We are done! + if (!SetBlobValueIfNeeded(ikey.user_key, iter_.value())) { + return false; + } + valid_ = true; + if (!Merge(&blob_value_, ikey.user_key)) { + return false; + } + + ResetBlobValue(); + + // iter_ is positioned after put + iter_.Next(); + if (!iter_.status().ok()) { + valid_ = false; + return false; + } + return true; + } else if (kTypeWideColumnEntity == ikey.type) { + if (!MergeEntity(iter_.value(), ikey.user_key)) { + return false; + } + + // iter_ is positioned after put + iter_.Next(); + if (!iter_.status().ok()) { + valid_ = false; + return false; + } + + return true; + } else { + valid_ = false; + status_ = Status::Corruption( + "Unrecognized value type: " + + std::to_string(static_cast<unsigned int>(ikey.type))); + return false; + } + } + + if (!iter_.status().ok()) { + valid_ = false; + return false; + } + + // we either exhausted all internal keys under this user key, or hit + // a deletion marker. + // feed null as the existing value to the merge operator, such that + // client can differentiate this scenario and do things accordingly. + if (!Merge(nullptr, saved_key_.GetUserKey())) { + return false; + } + assert(status_.ok()); + return true; +} + +void DBIter::Prev() { + assert(valid_); + assert(status_.ok()); + + PERF_CPU_TIMER_GUARD(iter_prev_cpu_nanos, clock_); + ReleaseTempPinnedData(); + ResetBlobValue(); + ResetValueAndColumns(); + ResetInternalKeysSkippedCounter(); + bool ok = true; + if (direction_ == kForward) { + if (!ReverseToBackward()) { + ok = false; + } + } + if (ok) { + ClearSavedValue(); + + Slice prefix; + if (prefix_same_as_start_) { + assert(prefix_extractor_ != nullptr); + prefix = prefix_.GetUserKey(); + } + PrevInternal(prefix_same_as_start_ ? &prefix : nullptr); + } + + if (statistics_ != nullptr) { + local_stats_.prev_count_++; + if (valid_) { + local_stats_.prev_found_count_++; + local_stats_.bytes_read_ += (key().size() + value().size()); + } + } +} + +bool DBIter::ReverseToForward() { + assert(iter_.status().ok()); + + // When moving backwards, iter_ is positioned on _previous_ key, which may + // not exist or may have different prefix than the current key(). + // If that's the case, seek iter_ to current key. + if (!expect_total_order_inner_iter() || !iter_.Valid()) { + IterKey last_key; + ParsedInternalKey pikey(saved_key_.GetUserKey(), kMaxSequenceNumber, + kValueTypeForSeek); + if (timestamp_size_ > 0) { + // TODO: pre-create kTsMax. + const std::string kTsMax(timestamp_size_, '\xff'); + pikey.SetTimestamp(kTsMax); + } + last_key.SetInternalKey(pikey); + iter_.Seek(last_key.GetInternalKey()); + RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION); + } + + direction_ = kForward; + // Skip keys less than the current key() (a.k.a. saved_key_). + while (iter_.Valid()) { + ParsedInternalKey ikey; + if (!ParseKey(&ikey)) { + return false; + } + if (user_comparator_.Compare(ikey.user_key, saved_key_.GetUserKey()) >= 0) { + return true; + } + iter_.Next(); + } + + if (!iter_.status().ok()) { + valid_ = false; + return false; + } + + return true; +} + +// Move iter_ to the key before saved_key_. +bool DBIter::ReverseToBackward() { + assert(iter_.status().ok()); + + // When current_entry_is_merged_ is true, iter_ may be positioned on the next + // key, which may not exist or may have prefix different from current. + // If that's the case, seek to saved_key_. + if (current_entry_is_merged_ && + (!expect_total_order_inner_iter() || !iter_.Valid())) { + IterKey last_key; + // Using kMaxSequenceNumber and kValueTypeForSeek + // (not kValueTypeForSeekForPrev) to seek to a key strictly smaller + // than saved_key_. + last_key.SetInternalKey(ParsedInternalKey( + saved_key_.GetUserKey(), kMaxSequenceNumber, kValueTypeForSeek)); + if (!expect_total_order_inner_iter()) { + iter_.SeekForPrev(last_key.GetInternalKey()); + } else { + // Some iterators may not support SeekForPrev(), so we avoid using it + // when prefix seek mode is disabled. This is somewhat expensive + // (an extra Prev(), as well as an extra change of direction of iter_), + // so we may need to reconsider it later. + iter_.Seek(last_key.GetInternalKey()); + if (!iter_.Valid() && iter_.status().ok()) { + iter_.SeekToLast(); + } + } + RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION); + } + + direction_ = kReverse; + return FindUserKeyBeforeSavedKey(); +} + +void DBIter::PrevInternal(const Slice* prefix) { + while (iter_.Valid()) { + saved_key_.SetUserKey( + ExtractUserKey(iter_.key()), + !iter_.iter()->IsKeyPinned() || !pin_thru_lifetime_ /* copy */); + + assert(prefix == nullptr || prefix_extractor_ != nullptr); + if (prefix != nullptr && + prefix_extractor_ + ->Transform(StripTimestampFromUserKey(saved_key_.GetUserKey(), + timestamp_size_)) + .compare(*prefix) != 0) { + assert(prefix_same_as_start_); + // Current key does not have the same prefix as start + valid_ = false; + return; + } + + assert(iterate_lower_bound_ == nullptr || iter_.MayBeOutOfLowerBound() || + user_comparator_.CompareWithoutTimestamp( + saved_key_.GetUserKey(), /*a_has_ts=*/true, + *iterate_lower_bound_, /*b_has_ts=*/false) >= 0); + if (iterate_lower_bound_ != nullptr && iter_.MayBeOutOfLowerBound() && + user_comparator_.CompareWithoutTimestamp( + saved_key_.GetUserKey(), /*a_has_ts=*/true, *iterate_lower_bound_, + /*b_has_ts=*/false) < 0) { + // We've iterated earlier than the user-specified lower bound. + valid_ = false; + return; + } + + if (!FindValueForCurrentKey()) { // assigns valid_ + return; + } + + // Whether or not we found a value for current key, we need iter_ to end up + // on a smaller key. + if (!FindUserKeyBeforeSavedKey()) { + return; + } + + if (valid_) { + // Found the value. + return; + } + + if (TooManyInternalKeysSkipped(false)) { + return; + } + } + + // We haven't found any key - iterator is not valid + valid_ = false; +} + +// Used for backwards iteration. +// Looks at the entries with user key saved_key_ and finds the most up-to-date +// value for it, or executes a merge, or determines that the value was deleted. +// Sets valid_ to true if the value is found and is ready to be presented to +// the user through value(). +// Sets valid_ to false if the value was deleted, and we should try another key. +// Returns false if an error occurred, and !status().ok() and !valid_. +// +// PRE: iter_ is positioned on the last entry with user key equal to saved_key_. +// POST: iter_ is positioned on one of the entries equal to saved_key_, or on +// the entry just before them, or on the entry just after them. +bool DBIter::FindValueForCurrentKey() { + assert(iter_.Valid()); + merge_context_.Clear(); + current_entry_is_merged_ = false; + // last entry before merge (could be kTypeDeletion, + // kTypeDeletionWithTimestamp, kTypeSingleDeletion, kTypeValue, + // kTypeBlobIndex, or kTypeWideColumnEntity) + ValueType last_not_merge_type = kTypeDeletion; + ValueType last_key_entry_type = kTypeDeletion; + + // If false, it indicates that we have not seen any valid entry, even though + // last_key_entry_type is initialized to kTypeDeletion. + bool valid_entry_seen = false; + + // Temporarily pin blocks that hold (merge operands / the value) + ReleaseTempPinnedData(); + TempPinData(); + size_t num_skipped = 0; + while (iter_.Valid()) { + ParsedInternalKey ikey; + if (!ParseKey(&ikey)) { + return false; + } + + if (!user_comparator_.EqualWithoutTimestamp(ikey.user_key, + saved_key_.GetUserKey())) { + // Found a smaller user key, thus we are done with current user key. + break; + } + + assert(ikey.user_key.size() >= timestamp_size_); + Slice ts; + if (timestamp_size_ > 0) { + ts = Slice(ikey.user_key.data() + ikey.user_key.size() - timestamp_size_, + timestamp_size_); + } + + bool visible = IsVisible(ikey.sequence, ts); + if (!visible && + (timestamp_lb_ == nullptr || + user_comparator_.CompareTimestamp(ts, *timestamp_ub_) > 0)) { + // Found an invisible version of the current user key, and it must have + // a higher sequence number or timestamp. Therefore, we are done with the + // current user key. + break; + } + + if (!ts.empty()) { + saved_timestamp_.assign(ts.data(), ts.size()); + } + + if (TooManyInternalKeysSkipped()) { + return false; + } + + // This user key has lots of entries. + // We're going from old to new, and it's taking too long. Let's do a Seek() + // and go from new to old. This helps when a key was overwritten many times. + if (num_skipped >= max_skip_) { + return FindValueForCurrentKeyUsingSeek(); + } + + if (!iter_.PrepareValue()) { + valid_ = false; + return false; + } + + if (timestamp_lb_ != nullptr) { + // Only needed when timestamp_lb_ is not null + [[maybe_unused]] const bool ret = ParseKey(&ikey_); + saved_ikey_.assign(iter_.key().data(), iter_.key().size()); + // Since the preceding ParseKey(&ikey) succeeds, so must this. + assert(ret); + } + + valid_entry_seen = true; + last_key_entry_type = ikey.type; + switch (last_key_entry_type) { + case kTypeValue: + case kTypeBlobIndex: + case kTypeWideColumnEntity: + if (iter_.iter()->IsValuePinned()) { + pinned_value_ = iter_.value(); + } else { + valid_ = false; + status_ = Status::NotSupported( + "Backward iteration not supported if underlying iterator's value " + "cannot be pinned."); + } + merge_context_.Clear(); + last_not_merge_type = last_key_entry_type; + if (!status_.ok()) { + return false; + } + break; + case kTypeDeletion: + case kTypeDeletionWithTimestamp: + case kTypeSingleDeletion: + merge_context_.Clear(); + last_not_merge_type = last_key_entry_type; + PERF_COUNTER_ADD(internal_delete_skipped_count, 1); + break; + case kTypeMerge: { + assert(merge_operator_ != nullptr); + merge_context_.PushOperandBack( + iter_.value(), iter_.iter()->IsValuePinned() /* operand_pinned */); + PERF_COUNTER_ADD(internal_merge_count, 1); + } break; + default: + valid_ = false; + status_ = Status::Corruption( + "Unknown value type: " + + std::to_string(static_cast<unsigned int>(last_key_entry_type))); + return false; + } + + PERF_COUNTER_ADD(internal_key_skipped_count, 1); + iter_.Prev(); + ++num_skipped; + + if (visible && timestamp_lb_ != nullptr) { + // If timestamp_lb_ is not nullptr, we do not have to look further for + // another internal key. We can return this current internal key. Yet we + // still keep the invariant that iter_ is positioned before the returned + // key. + break; + } + } + + if (!iter_.status().ok()) { + valid_ = false; + return false; + } + + if (!valid_entry_seen) { + // Since we haven't seen any valid entry, last_key_entry_type remains + // unchanged and the same as its initial value. + assert(last_key_entry_type == kTypeDeletion); + assert(last_not_merge_type == kTypeDeletion); + valid_ = false; + return true; + } + + if (timestamp_lb_ != nullptr) { + assert(last_key_entry_type == ikey_.type); + } + + Status s; + s.PermitUncheckedError(); + + switch (last_key_entry_type) { + case kTypeDeletion: + case kTypeDeletionWithTimestamp: + case kTypeSingleDeletion: + if (timestamp_lb_ == nullptr) { + valid_ = false; + } else { + saved_key_.SetInternalKey(saved_ikey_); + valid_ = true; + } + return true; + case kTypeMerge: + current_entry_is_merged_ = true; + if (last_not_merge_type == kTypeDeletion || + last_not_merge_type == kTypeSingleDeletion || + last_not_merge_type == kTypeDeletionWithTimestamp) { + if (!Merge(nullptr, saved_key_.GetUserKey())) { + return false; + } + return true; + } else if (last_not_merge_type == kTypeBlobIndex) { + if (expose_blob_index_) { + status_ = + Status::NotSupported("BlobDB does not support merge operator."); + valid_ = false; + return false; + } + if (!SetBlobValueIfNeeded(saved_key_.GetUserKey(), pinned_value_)) { + return false; + } + valid_ = true; + if (!Merge(&blob_value_, saved_key_.GetUserKey())) { + return false; + } + + ResetBlobValue(); + + return true; + } else if (last_not_merge_type == kTypeWideColumnEntity) { + if (!MergeEntity(pinned_value_, saved_key_.GetUserKey())) { + return false; + } + + return true; + } else { + assert(last_not_merge_type == kTypeValue); + if (!Merge(&pinned_value_, saved_key_.GetUserKey())) { + return false; + } + return true; + } + break; + case kTypeValue: + if (timestamp_lb_ != nullptr) { + saved_key_.SetInternalKey(saved_ikey_); + } + + SetValueAndColumnsFromPlain(pinned_value_); + + break; + case kTypeBlobIndex: + if (!SetBlobValueIfNeeded(saved_key_.GetUserKey(), pinned_value_)) { + return false; + } + + SetValueAndColumnsFromPlain(expose_blob_index_ ? pinned_value_ + : blob_value_); + + break; + case kTypeWideColumnEntity: + if (!SetValueAndColumnsFromEntity(pinned_value_)) { + return false; + } + break; + default: + valid_ = false; + status_ = Status::Corruption( + "Unknown value type: " + + std::to_string(static_cast<unsigned int>(last_key_entry_type))); + return false; + } + if (!s.ok()) { + valid_ = false; + status_ = s; + return false; + } + valid_ = true; + return true; +} + +// This function is used in FindValueForCurrentKey. +// We use Seek() function instead of Prev() to find necessary value +// TODO: This is very similar to FindNextUserEntry() and MergeValuesNewToOld(). +// Would be nice to reuse some code. +bool DBIter::FindValueForCurrentKeyUsingSeek() { + // FindValueForCurrentKey will enable pinning before calling + // FindValueForCurrentKeyUsingSeek() + assert(pinned_iters_mgr_.PinningEnabled()); + std::string last_key; + if (0 == timestamp_size_) { + AppendInternalKey(&last_key, + ParsedInternalKey(saved_key_.GetUserKey(), sequence_, + kValueTypeForSeek)); + } else { + AppendInternalKeyWithDifferentTimestamp( + &last_key, + ParsedInternalKey(saved_key_.GetUserKey(), sequence_, + kValueTypeForSeek), + timestamp_lb_ == nullptr ? *timestamp_ub_ : *timestamp_lb_); + } + iter_.Seek(last_key); + RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION); + + // In case read_callback presents, the value we seek to may not be visible. + // Find the next value that's visible. + ParsedInternalKey ikey; + + while (true) { + if (!iter_.Valid()) { + valid_ = false; + return iter_.status().ok(); + } + + if (!ParseKey(&ikey)) { + return false; + } + assert(ikey.user_key.size() >= timestamp_size_); + Slice ts; + if (timestamp_size_ > 0) { + ts = Slice(ikey.user_key.data() + ikey.user_key.size() - timestamp_size_, + timestamp_size_); + } + + if (!user_comparator_.EqualWithoutTimestamp(ikey.user_key, + saved_key_.GetUserKey())) { + // No visible values for this key, even though FindValueForCurrentKey() + // has seen some. This is possible if we're using a tailing iterator, and + // the entries were discarded in a compaction. + valid_ = false; + return true; + } + + if (IsVisible(ikey.sequence, ts)) { + break; + } + + iter_.Next(); + } + + if (ikey.type == kTypeDeletion || ikey.type == kTypeSingleDeletion || + kTypeDeletionWithTimestamp == ikey.type) { + if (timestamp_lb_ == nullptr) { + valid_ = false; + } else { + valid_ = true; + saved_key_.SetInternalKey(ikey); + } + return true; + } + if (!iter_.PrepareValue()) { + valid_ = false; + return false; + } + if (timestamp_size_ > 0) { + Slice ts = ExtractTimestampFromUserKey(ikey.user_key, timestamp_size_); + saved_timestamp_.assign(ts.data(), ts.size()); + } + if (ikey.type == kTypeValue || ikey.type == kTypeBlobIndex || + ikey.type == kTypeWideColumnEntity) { + assert(iter_.iter()->IsValuePinned()); + pinned_value_ = iter_.value(); + if (ikey.type == kTypeBlobIndex) { + if (!SetBlobValueIfNeeded(ikey.user_key, pinned_value_)) { + return false; + } + + SetValueAndColumnsFromPlain(expose_blob_index_ ? pinned_value_ + : blob_value_); + } else if (ikey.type == kTypeWideColumnEntity) { + if (!SetValueAndColumnsFromEntity(pinned_value_)) { + return false; + } + } else { + assert(ikey.type == kTypeValue); + SetValueAndColumnsFromPlain(pinned_value_); + } + + if (timestamp_lb_ != nullptr) { + saved_key_.SetInternalKey(ikey); + } + + valid_ = true; + return true; + } + + // kTypeMerge. We need to collect all kTypeMerge values and save them + // in operands + assert(ikey.type == kTypeMerge); + current_entry_is_merged_ = true; + merge_context_.Clear(); + merge_context_.PushOperand( + iter_.value(), iter_.iter()->IsValuePinned() /* operand_pinned */); + while (true) { + iter_.Next(); + + if (!iter_.Valid()) { + if (!iter_.status().ok()) { + valid_ = false; + return false; + } + break; + } + if (!ParseKey(&ikey)) { + return false; + } + if (!user_comparator_.EqualWithoutTimestamp(ikey.user_key, + saved_key_.GetUserKey())) { + break; + } + if (ikey.type == kTypeDeletion || ikey.type == kTypeSingleDeletion || + ikey.type == kTypeDeletionWithTimestamp) { + break; + } + if (!iter_.PrepareValue()) { + valid_ = false; + return false; + } + + if (ikey.type == kTypeValue) { + const Slice val = iter_.value(); + if (!Merge(&val, saved_key_.GetUserKey())) { + return false; + } + return true; + } else if (ikey.type == kTypeMerge) { + merge_context_.PushOperand( + iter_.value(), iter_.iter()->IsValuePinned() /* operand_pinned */); + PERF_COUNTER_ADD(internal_merge_count, 1); + } else if (ikey.type == kTypeBlobIndex) { + if (expose_blob_index_) { + status_ = + Status::NotSupported("BlobDB does not support merge operator."); + valid_ = false; + return false; + } + if (!SetBlobValueIfNeeded(ikey.user_key, iter_.value())) { + return false; + } + valid_ = true; + if (!Merge(&blob_value_, saved_key_.GetUserKey())) { + return false; + } + + ResetBlobValue(); + + return true; + } else if (ikey.type == kTypeWideColumnEntity) { + if (!MergeEntity(iter_.value(), saved_key_.GetUserKey())) { + return false; + } + + return true; + } else { + valid_ = false; + status_ = Status::Corruption( + "Unknown value type: " + + std::to_string(static_cast<unsigned int>(ikey.type))); + return false; + } + } + + if (!Merge(nullptr, saved_key_.GetUserKey())) { + return false; + } + + // Make sure we leave iter_ in a good state. If it's valid and we don't care + // about prefixes, that's already good enough. Otherwise it needs to be + // seeked to the current key. + if (!expect_total_order_inner_iter() || !iter_.Valid()) { + if (!expect_total_order_inner_iter()) { + iter_.SeekForPrev(last_key); + } else { + iter_.Seek(last_key); + if (!iter_.Valid() && iter_.status().ok()) { + iter_.SeekToLast(); + } + } + RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION); + } + + valid_ = true; + return true; +} + +bool DBIter::Merge(const Slice* val, const Slice& user_key) { + Status s = MergeHelper::TimedFullMerge( + merge_operator_, user_key, val, merge_context_.GetOperands(), + &saved_value_, logger_, statistics_, clock_, &pinned_value_, + /* update_num_ops_stats */ true); + if (!s.ok()) { + valid_ = false; + status_ = s; + return false; + } + + SetValueAndColumnsFromPlain(pinned_value_.data() ? pinned_value_ + : saved_value_); + + valid_ = true; + return true; +} + +bool DBIter::MergeEntity(const Slice& entity, const Slice& user_key) { + Status s = MergeHelper::TimedFullMergeWithEntity( + merge_operator_, user_key, entity, merge_context_.GetOperands(), + &saved_value_, logger_, statistics_, clock_, + /* update_num_ops_stats */ true); + if (!s.ok()) { + valid_ = false; + status_ = s; + return false; + } + + if (!SetValueAndColumnsFromEntity(saved_value_)) { + return false; + } + + valid_ = true; + return true; +} + +// Move backwards until the key smaller than saved_key_. +// Changes valid_ only if return value is false. +bool DBIter::FindUserKeyBeforeSavedKey() { + assert(status_.ok()); + size_t num_skipped = 0; + while (iter_.Valid()) { + ParsedInternalKey ikey; + if (!ParseKey(&ikey)) { + return false; + } + + if (CompareKeyForSkip(ikey.user_key, saved_key_.GetUserKey()) < 0) { + return true; + } + + if (TooManyInternalKeysSkipped()) { + return false; + } + + assert(ikey.sequence != kMaxSequenceNumber); + assert(ikey.user_key.size() >= timestamp_size_); + Slice ts; + if (timestamp_size_ > 0) { + ts = Slice(ikey.user_key.data() + ikey.user_key.size() - timestamp_size_, + timestamp_size_); + } + if (!IsVisible(ikey.sequence, ts)) { + PERF_COUNTER_ADD(internal_recent_skipped_count, 1); + } else { + PERF_COUNTER_ADD(internal_key_skipped_count, 1); + } + + if (num_skipped >= max_skip_) { + num_skipped = 0; + IterKey last_key; + ParsedInternalKey pikey(saved_key_.GetUserKey(), kMaxSequenceNumber, + kValueTypeForSeek); + if (timestamp_size_ > 0) { + // TODO: pre-create kTsMax. + const std::string kTsMax(timestamp_size_, '\xff'); + pikey.SetTimestamp(kTsMax); + } + last_key.SetInternalKey(pikey); + // It would be more efficient to use SeekForPrev() here, but some + // iterators may not support it. + iter_.Seek(last_key.GetInternalKey()); + RecordTick(statistics_, NUMBER_OF_RESEEKS_IN_ITERATION); + if (!iter_.Valid()) { + break; + } + } else { + ++num_skipped; + } + + iter_.Prev(); + } + + if (!iter_.status().ok()) { + valid_ = false; + return false; + } + + return true; +} + +bool DBIter::TooManyInternalKeysSkipped(bool increment) { + if ((max_skippable_internal_keys_ > 0) && + (num_internal_keys_skipped_ > max_skippable_internal_keys_)) { + valid_ = false; + status_ = Status::Incomplete("Too many internal keys skipped."); + return true; + } else if (increment) { + num_internal_keys_skipped_++; + } + return false; +} + +bool DBIter::IsVisible(SequenceNumber sequence, const Slice& ts, + bool* more_recent) { + // Remember that comparator orders preceding timestamp as larger. + // TODO(yanqin): support timestamp in read_callback_. + bool visible_by_seq = (read_callback_ == nullptr) + ? sequence <= sequence_ + : read_callback_->IsVisible(sequence); + + bool visible_by_ts = + (timestamp_ub_ == nullptr || + user_comparator_.CompareTimestamp(ts, *timestamp_ub_) <= 0) && + (timestamp_lb_ == nullptr || + user_comparator_.CompareTimestamp(ts, *timestamp_lb_) >= 0); + + if (more_recent) { + *more_recent = !visible_by_seq; + } + return visible_by_seq && visible_by_ts; +} + +void DBIter::SetSavedKeyToSeekTarget(const Slice& target) { + is_key_seqnum_zero_ = false; + SequenceNumber seq = sequence_; + saved_key_.Clear(); + saved_key_.SetInternalKey(target, seq, kValueTypeForSeek, timestamp_ub_); + + if (iterate_lower_bound_ != nullptr && + user_comparator_.CompareWithoutTimestamp( + saved_key_.GetUserKey(), /*a_has_ts=*/true, *iterate_lower_bound_, + /*b_has_ts=*/false) < 0) { + // Seek key is smaller than the lower bound. + saved_key_.Clear(); + saved_key_.SetInternalKey(*iterate_lower_bound_, seq, kValueTypeForSeek, + timestamp_ub_); + } +} + +void DBIter::SetSavedKeyToSeekForPrevTarget(const Slice& target) { + is_key_seqnum_zero_ = false; + saved_key_.Clear(); + // now saved_key is used to store internal key. + saved_key_.SetInternalKey(target, 0 /* sequence_number */, + kValueTypeForSeekForPrev, timestamp_ub_); + + if (timestamp_size_ > 0) { + const std::string kTsMin(timestamp_size_, '\0'); + Slice ts = kTsMin; + saved_key_.UpdateInternalKey( + /*seq=*/0, kValueTypeForSeekForPrev, + timestamp_lb_ == nullptr ? &ts : timestamp_lb_); + } + + if (iterate_upper_bound_ != nullptr && + user_comparator_.CompareWithoutTimestamp( + saved_key_.GetUserKey(), /*a_has_ts=*/true, *iterate_upper_bound_, + /*b_has_ts=*/false) >= 0) { + saved_key_.Clear(); + saved_key_.SetInternalKey(*iterate_upper_bound_, kMaxSequenceNumber, + kValueTypeForSeekForPrev, timestamp_ub_); + if (timestamp_size_ > 0) { + const std::string kTsMax(timestamp_size_, '\xff'); + Slice ts = kTsMax; + saved_key_.UpdateInternalKey( + kMaxSequenceNumber, kValueTypeForSeekForPrev, + timestamp_lb_ != nullptr ? timestamp_lb_ : &ts); + } + } +} + +void DBIter::Seek(const Slice& target) { + PERF_CPU_TIMER_GUARD(iter_seek_cpu_nanos, clock_); + StopWatch sw(clock_, statistics_, DB_SEEK); + +#ifndef ROCKSDB_LITE + if (db_impl_ != nullptr && cfd_ != nullptr) { + // TODO: What do we do if this returns an error? + Slice lower_bound, upper_bound; + if (iterate_lower_bound_ != nullptr) { + lower_bound = *iterate_lower_bound_; + } else { + lower_bound = Slice(""); + } + if (iterate_upper_bound_ != nullptr) { + upper_bound = *iterate_upper_bound_; + } else { + upper_bound = Slice(""); + } + db_impl_->TraceIteratorSeek(cfd_->GetID(), target, lower_bound, upper_bound) + .PermitUncheckedError(); + } +#endif // ROCKSDB_LITE + + status_ = Status::OK(); + ReleaseTempPinnedData(); + ResetBlobValue(); + ResetValueAndColumns(); + ResetInternalKeysSkippedCounter(); + + // Seek the inner iterator based on the target key. + { + PERF_TIMER_GUARD(seek_internal_seek_time); + + SetSavedKeyToSeekTarget(target); + iter_.Seek(saved_key_.GetInternalKey()); + + RecordTick(statistics_, NUMBER_DB_SEEK); + } + if (!iter_.Valid()) { + valid_ = false; + return; + } + direction_ = kForward; + + // Now the inner iterator is placed to the target position. From there, + // we need to find out the next key that is visible to the user. + ClearSavedValue(); + if (prefix_same_as_start_) { + // The case where the iterator needs to be invalidated if it has exhausted + // keys within the same prefix of the seek key. + assert(prefix_extractor_ != nullptr); + Slice target_prefix = prefix_extractor_->Transform(target); + FindNextUserEntry(false /* not skipping saved_key */, + &target_prefix /* prefix */); + if (valid_) { + // Remember the prefix of the seek key for the future Next() call to + // check. + prefix_.SetUserKey(target_prefix); + } + } else { + FindNextUserEntry(false /* not skipping saved_key */, nullptr); + } + if (!valid_) { + return; + } + + // Updating stats and perf context counters. + if (statistics_ != nullptr) { + // Decrement since we don't want to count this key as skipped + RecordTick(statistics_, NUMBER_DB_SEEK_FOUND); + RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size()); + } + PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size()); +} + +void DBIter::SeekForPrev(const Slice& target) { + PERF_CPU_TIMER_GUARD(iter_seek_cpu_nanos, clock_); + StopWatch sw(clock_, statistics_, DB_SEEK); + +#ifndef ROCKSDB_LITE + if (db_impl_ != nullptr && cfd_ != nullptr) { + // TODO: What do we do if this returns an error? + Slice lower_bound, upper_bound; + if (iterate_lower_bound_ != nullptr) { + lower_bound = *iterate_lower_bound_; + } else { + lower_bound = Slice(""); + } + if (iterate_upper_bound_ != nullptr) { + upper_bound = *iterate_upper_bound_; + } else { + upper_bound = Slice(""); + } + db_impl_ + ->TraceIteratorSeekForPrev(cfd_->GetID(), target, lower_bound, + upper_bound) + .PermitUncheckedError(); + } +#endif // ROCKSDB_LITE + + status_ = Status::OK(); + ReleaseTempPinnedData(); + ResetBlobValue(); + ResetValueAndColumns(); + ResetInternalKeysSkippedCounter(); + + // Seek the inner iterator based on the target key. + { + PERF_TIMER_GUARD(seek_internal_seek_time); + SetSavedKeyToSeekForPrevTarget(target); + iter_.SeekForPrev(saved_key_.GetInternalKey()); + RecordTick(statistics_, NUMBER_DB_SEEK); + } + if (!iter_.Valid()) { + valid_ = false; + return; + } + direction_ = kReverse; + + // Now the inner iterator is placed to the target position. From there, + // we need to find out the first key that is visible to the user in the + // backward direction. + ClearSavedValue(); + if (prefix_same_as_start_) { + // The case where the iterator needs to be invalidated if it has exhausted + // keys within the same prefix of the seek key. + assert(prefix_extractor_ != nullptr); + Slice target_prefix = prefix_extractor_->Transform(target); + PrevInternal(&target_prefix); + if (valid_) { + // Remember the prefix of the seek key for the future Prev() call to + // check. + prefix_.SetUserKey(target_prefix); + } + } else { + PrevInternal(nullptr); + } + + // Report stats and perf context. + if (statistics_ != nullptr && valid_) { + RecordTick(statistics_, NUMBER_DB_SEEK_FOUND); + RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size()); + PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size()); + } +} + +void DBIter::SeekToFirst() { + if (iterate_lower_bound_ != nullptr) { + Seek(*iterate_lower_bound_); + return; + } + PERF_CPU_TIMER_GUARD(iter_seek_cpu_nanos, clock_); + // Don't use iter_::Seek() if we set a prefix extractor + // because prefix seek will be used. + if (!expect_total_order_inner_iter()) { + max_skip_ = std::numeric_limits<uint64_t>::max(); + } + status_ = Status::OK(); + // if iterator is empty, this status_ could be unchecked. + status_.PermitUncheckedError(); + direction_ = kForward; + ReleaseTempPinnedData(); + ResetBlobValue(); + ResetValueAndColumns(); + ResetInternalKeysSkippedCounter(); + ClearSavedValue(); + is_key_seqnum_zero_ = false; + + { + PERF_TIMER_GUARD(seek_internal_seek_time); + iter_.SeekToFirst(); + } + + RecordTick(statistics_, NUMBER_DB_SEEK); + if (iter_.Valid()) { + saved_key_.SetUserKey( + ExtractUserKey(iter_.key()), + !iter_.iter()->IsKeyPinned() || !pin_thru_lifetime_ /* copy */); + FindNextUserEntry(false /* not skipping saved_key */, + nullptr /* no prefix check */); + if (statistics_ != nullptr) { + if (valid_) { + RecordTick(statistics_, NUMBER_DB_SEEK_FOUND); + RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size()); + PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size()); + } + } + } else { + valid_ = false; + } + if (valid_ && prefix_same_as_start_) { + assert(prefix_extractor_ != nullptr); + prefix_.SetUserKey(prefix_extractor_->Transform( + StripTimestampFromUserKey(saved_key_.GetUserKey(), timestamp_size_))); + } +} + +void DBIter::SeekToLast() { + if (iterate_upper_bound_ != nullptr) { + // Seek to last key strictly less than ReadOptions.iterate_upper_bound. + SeekForPrev(*iterate_upper_bound_); + const bool is_ikey = (timestamp_size_ > 0 && timestamp_lb_ != nullptr); + Slice k = Valid() ? key() : Slice(); + if (is_ikey && Valid()) { + k.remove_suffix(kNumInternalBytes + timestamp_size_); + } + while (Valid() && 0 == user_comparator_.CompareWithoutTimestamp( + *iterate_upper_bound_, /*a_has_ts=*/false, k, + /*b_has_ts=*/false)) { + ReleaseTempPinnedData(); + ResetBlobValue(); + ResetValueAndColumns(); + PrevInternal(nullptr); + + k = key(); + if (is_ikey) { + k.remove_suffix(kNumInternalBytes + timestamp_size_); + } + } + return; + } + + PERF_CPU_TIMER_GUARD(iter_seek_cpu_nanos, clock_); + // Don't use iter_::Seek() if we set a prefix extractor + // because prefix seek will be used. + if (!expect_total_order_inner_iter()) { + max_skip_ = std::numeric_limits<uint64_t>::max(); + } + status_ = Status::OK(); + // if iterator is empty, this status_ could be unchecked. + status_.PermitUncheckedError(); + direction_ = kReverse; + ReleaseTempPinnedData(); + ResetBlobValue(); + ResetValueAndColumns(); + ResetInternalKeysSkippedCounter(); + ClearSavedValue(); + is_key_seqnum_zero_ = false; + + { + PERF_TIMER_GUARD(seek_internal_seek_time); + iter_.SeekToLast(); + } + PrevInternal(nullptr); + if (statistics_ != nullptr) { + RecordTick(statistics_, NUMBER_DB_SEEK); + if (valid_) { + RecordTick(statistics_, NUMBER_DB_SEEK_FOUND); + RecordTick(statistics_, ITER_BYTES_READ, key().size() + value().size()); + PERF_COUNTER_ADD(iter_read_bytes, key().size() + value().size()); + } + } + if (valid_ && prefix_same_as_start_) { + assert(prefix_extractor_ != nullptr); + prefix_.SetUserKey(prefix_extractor_->Transform( + StripTimestampFromUserKey(saved_key_.GetUserKey(), timestamp_size_))); + } +} + +Iterator* NewDBIterator(Env* env, const ReadOptions& read_options, + const ImmutableOptions& ioptions, + const MutableCFOptions& mutable_cf_options, + const Comparator* user_key_comparator, + InternalIterator* internal_iter, const Version* version, + const SequenceNumber& sequence, + uint64_t max_sequential_skip_in_iterations, + ReadCallback* read_callback, DBImpl* db_impl, + ColumnFamilyData* cfd, bool expose_blob_index) { + DBIter* db_iter = + new DBIter(env, read_options, ioptions, mutable_cf_options, + user_key_comparator, internal_iter, version, sequence, false, + max_sequential_skip_in_iterations, read_callback, db_impl, cfd, + expose_blob_index); + return db_iter; +} + +} // namespace ROCKSDB_NAMESPACE |