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db_iter.cc
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db_iter.cc
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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.
#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 "db/wide/wide_columns_helper.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, ColumnFamilyHandleImpl* cfh,
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),
io_activity_(read_options.io_activity),
cfh_(cfh),
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();
} else if (prop_name == "rocksdb.iterator.write-time") {
PutFixed64(prop, saved_write_unix_time_);
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_COUNTER_ADD(iter_next_count, 1);
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.
// TODO: plumb Env::IOActivity, Env::IOPriority
ReadOptions read_options;
read_options.read_tier = read_tier_;
read_options.fill_cache = fill_cache_;
read_options.verify_checksums = verify_checksums_;
read_options.io_activity = io_activity_;
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 (WideColumnsHelper::HasDefaultColumn(wide_columns_)) {
value_ = WideColumnsHelper::GetDefaultColumn(wide_columns_);
}
return true;
}
bool DBIter::SetValueAndColumnsFromMergeResult(const Status& merge_status,
ValueType result_type) {
if (!merge_status.ok()) {
valid_ = false;
status_ = merge_status;
return false;
}
if (result_type == kTypeWideColumnEntity) {
if (!SetValueAndColumnsFromEntity(saved_value_)) {
assert(!valid_);
return false;
}
valid_ = true;
return true;
}
assert(result_type == kTypeValue);
SetValueAndColumnsFromPlain(pinned_value_.data() ? pinned_value_
: saved_value_);
valid_ = true;
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);
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 kTypeValuePreferredSeqno:
case kTypeBlobIndex:
case kTypeWideColumnEntity:
if (!PrepareValue()) {
return false;
}
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 ||
ikey_.type == kTypeValuePreferredSeqno);
Slice value = iter_.value();
saved_write_unix_time_ = iter_.write_unix_time();
if (ikey_.type == kTypeValuePreferredSeqno) {
value = ParsePackedValueForValue(value);
}
SetValueAndColumnsFromPlain(value);
}
valid_ = true;
return true;
break;
case kTypeMerge:
if (!PrepareValue()) {
return false;
}
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 */);
PERF_COUNTER_ADD(internal_merge_count, 1);
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 (!PrepareValue()) {
return false;
}
if (kTypeValue == ikey.type || kTypeValuePreferredSeqno == ikey.type) {
Slice value = iter_.value();
saved_write_unix_time_ = iter_.write_unix_time();
if (kTypeValuePreferredSeqno == ikey.type) {
value = ParsePackedValueForValue(value);
}
// hit a put or put equivalent, merge the put value with operands and
// store the final result in saved_value_. We are done!
if (!MergeWithPlainBaseValue(value, 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 (!MergeWithPlainBaseValue(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 (!MergeWithWideColumnBaseValue(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 (!MergeWithNoBaseValue(saved_key_.GetUserKey())) {
return false;
}
assert(status_.ok());
return true;
}
void DBIter::Prev() {
assert(valid_);
assert(status_.ok());
PERF_COUNTER_ADD(iter_prev_count, 1);
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()) {
std::string last_key;
if (timestamp_size_ == 0) {
AppendInternalKey(
&last_key, ParsedInternalKey(saved_key_.GetUserKey(),
kMaxSequenceNumber, kValueTypeForSeek));
} else {
// TODO: pre-create kTsMax.
const std::string kTsMax(timestamp_size_, '\xff');
AppendInternalKeyWithDifferentTimestamp(
&last_key,
ParsedInternalKey(saved_key_.GetUserKey(), kMaxSequenceNumber,
kValueTypeForSeek),
kTsMax);
}
iter_.Seek(last_key);
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, kTypeWideColumnEntity or kTypeValuePreferredSeqno)
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 (!PrepareValue()) {
return false;
}
if (timestamp_lb_ != nullptr) {
// Only needed when timestamp_lb_ is not null
[[maybe_unused]] const bool ret = ParseKey(&ikey_);
// Since the preceding ParseKey(&ikey) succeeds, so must this.
assert(ret);
saved_key_.SetInternalKey(ikey);
} else if (user_comparator_.Compare(ikey.user_key,
saved_key_.GetUserKey()) < 0) {
saved_key_.SetUserKey(
ikey.user_key,
!pin_thru_lifetime_ || !iter_.iter()->IsKeyPinned() /* copy */);
}
valid_entry_seen = true;
last_key_entry_type = ikey.type;
switch (last_key_entry_type) {
case kTypeValue:
case kTypeValuePreferredSeqno:
case kTypeBlobIndex:
case kTypeWideColumnEntity:
if (iter_.iter()->IsValuePinned()) {
saved_write_unix_time_ = iter_.write_unix_time();
if (last_key_entry_type == kTypeValuePreferredSeqno) {
pinned_value_ = ParsePackedValueForValue(iter_.value());
} else {
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.