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rocksdb/db/db_iter.cc
Changyu Bi 30bc495c03 Skip swaths of range tombstone covered keys in merging iterator (2022 edition) (#10449) 
Summary:
Delete range logic is moved from `DBIter` to `MergingIterator`, and `MergingIterator` will seek to the end of a range deletion if possible instead of scanning through each key and check with `RangeDelAggregator`.

With the invariant that a key in level L (consider memtable as the first level, each immutable and L0 as a separate level) has a larger sequence number than all keys in any level >L, a range tombstone `[start, end)` from level L covers all keys in its range in any level >L. This property motivates optimizations in iterator:
- in `Seek(target)`, if level L has a range tombstone `[start, end)` that covers `target.UserKey`, then for all levels > L, we can do Seek() on `end` instead of `target` to skip some range tombstone covered keys.
- in `Next()/Prev()`, if the current key is covered by a range tombstone `[start, end)` from level L, we can do `Seek` to `end` for all levels > L.

This PR implements the above optimizations in `MergingIterator`. As all range tombstone covered keys are now skipped in `MergingIterator`, the range tombstone logic is removed from `DBIter`. The idea in this PR is similar to https://github.com/facebook/rocksdb/issues/7317, but this PR leaves `InternalIterator` interface mostly unchanged. **Credit**: the cascading seek optimization and the sentinel key (discussed below) are inspired by [Pebble](https://github.com/cockroachdb/pebble/blob/master/merging_iter.go) and suggested by ajkr in https://github.com/facebook/rocksdb/issues/7317. The two optimizations are mostly implemented in `SeekImpl()/SeekForPrevImpl()` and `IsNextDeleted()/IsPrevDeleted()` in `merging_iterator.cc`. See comments for each method for more detail.

One notable change is that the minHeap/maxHeap used by `MergingIterator` now contains range tombstone end keys besides point key iterators. This helps to reduce the number of key comparisons. For example, for a range tombstone `[start, end)`, a `start` and an `end` `HeapItem` are inserted into the heap. When a `HeapItem` for range tombstone start key is popped from the minHeap, we know this range tombstone becomes "active" in the sense that, before the range tombstone's end key is popped from the minHeap, all the keys popped from this heap is covered by the range tombstone's internal key range `[start, end)`.

Another major change, *delete range sentinel key*, is made to `LevelIterator`. Before this PR, when all point keys in an SST file are iterated through in `MergingIterator`, a level iterator would advance to the next SST file in its level. In the case when an SST file has a range tombstone that covers keys beyond the SST file's last point key, advancing to the next SST file would lose this range tombstone. Consequently, `MergingIterator` could return keys that should have been deleted by some range tombstone. We prevent this by pretending that file boundaries in each SST file are sentinel keys. A `LevelIterator` now only advance the file iterator once the sentinel key is processed.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10449

Test Plan:
- Added many unit tests in db_range_del_test
- Stress test: `./db_stress --readpercent=5 --prefixpercent=19 --writepercent=20 -delpercent=10 --iterpercent=44 --delrangepercent=2`
- Additional iterator stress test is added to verify against iterators against expected state: https://github.com/facebook/rocksdb/issues/10538. This is based on ajkr's previous attempt https://github.com/facebook/rocksdb/pull/5506#issuecomment-506021913.

```
python3 ./tools/db_crashtest.py blackbox --simple --write_buffer_size=524288 --target_file_size_base=524288 --max_bytes_for_level_base=2097152 --compression_type=none --max_background_compactions=8 --value_size_mult=33 --max_key=5000000 --interval=10 --duration=7200 --delrangepercent=3 --delpercent=9 --iterpercent=25 --writepercent=60 --readpercent=3 --prefixpercent=0 --num_iterations=1000 --range_deletion_width=100 --verify_iterator_with_expected_state_one_in=1
```

- Performance benchmark: I used a similar setup as in the blog [post](http://rocksdb.org/blog/2018/11/21/delete-range.html) that introduced DeleteRange, "a database with 5 million data keys, and 10000 range tombstones (ignoring those dropped during compaction) that were written in regular intervals after 4.5 million data keys were written".  As expected, the performance with this PR depends on the range tombstone width.
```
# Setup:
TEST_TMPDIR=/dev/shm ./db_bench_main --benchmarks=fillrandom --writes=4500000 --num=5000000
TEST_TMPDIR=/dev/shm ./db_bench_main --benchmarks=overwrite --writes=500000 --num=5000000 --use_existing_db=true --writes_per_range_tombstone=50

# Scan entire DB
TEST_TMPDIR=/dev/shm ./db_bench_main --benchmarks=readseq[-X5] --use_existing_db=true --num=5000000 --disable_auto_compactions=true

# Short range scan (10 Next())
TEST_TMPDIR=/dev/shm/width-100/ ./db_bench_main --benchmarks=seekrandom[-X5] --use_existing_db=true --num=500000 --reads=100000 --seek_nexts=10 --disable_auto_compactions=true

# Long range scan(1000 Next())
TEST_TMPDIR=/dev/shm/width-100/ ./db_bench_main --benchmarks=seekrandom[-X5] --use_existing_db=true --num=500000 --reads=2500 --seek_nexts=1000 --disable_auto_compactions=true
```
Avg over of 10 runs (some slower tests had fews runs):

For the first column (tombstone), 0 means no range tombstone, 100-10000 means width of the 10k range tombstones, and 1 means there is a single range tombstone in the entire DB (width is 1000). The 1 tombstone case is to test regression when there's very few range tombstones in the DB, as no range tombstone is likely to take a different code path than with range tombstones.

- Scan entire DB

| tombstone width | Pre-PR ops/sec | Post-PR ops/sec | ±% |
| ------------- | ------------- | ------------- |  ------------- |
| 0 range tombstone    |2525600 (± 43564)    |2486917 (± 33698)    |-1.53%               |
| 100   |1853835 (± 24736)    |2073884 (± 32176)    |+11.87%              |
| 1000  |422415 (± 7466)      |1115801 (± 22781)    |+164.15%             |
| 10000 |22384 (± 227)        |227919 (± 6647)      |+918.22%             |
| 1 range tombstone      |2176540 (± 39050)    |2434954 (± 24563)    |+11.87%              |
- Short range scan

| tombstone width | Pre-PR ops/sec | Post-PR ops/sec | ±% |
| ------------- | ------------- | ------------- |  ------------- |
| 0  range tombstone   |35398 (± 533)        |35338 (± 569)        |-0.17%               |
| 100   |28276 (± 664)        |31684 (± 331)        |+12.05%              |
| 1000  |7637 (± 77)          |25422 (± 277)        |+232.88%             |
| 10000 |1367                 |28667                |+1997.07%            |
| 1 range tombstone      |32618 (± 581)        |32748 (± 506)        |+0.4%                |

- Long range scan

| tombstone width | Pre-PR ops/sec | Post-PR ops/sec | ±% |
| ------------- | ------------- | ------------- |  ------------- |
| 0 range tombstone     |2262 (± 33)          |2353 (± 20)          |+4.02%               |
| 100   |1696 (± 26)          |1926 (± 18)          |+13.56%              |
| 1000  |410 (± 6)            |1255 (± 29)          |+206.1%              |
| 10000 |25                   |414                  |+1556.0%             |
| 1 range tombstone   |1957 (± 30)          |2185 (± 44)          |+11.65%              |

- Microbench does not show significant regression: https://gist.github.com/cbi42/59f280f85a59b678e7e5d8561e693b61

Reviewed By: ajkr

Differential Revision: D38450331

Pulled By: cbi42

fbshipit-source-id: b5ef12e8d8c289ed2e163ccdf277f5039b511fca
2022-09-02 09:51:19 -07:00

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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 "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),
is_wide_(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_);
}
assert(timestamp_size_ == 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();
ResetWideColumnValue();
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()) {
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());
assert(!is_wide_);
assert(value_of_default_column_.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::SetWideColumnValueIfNeeded(const Slice& wide_columns_slice) {
assert(!is_blob_);
assert(blob_value_.empty());
assert(!is_wide_);
assert(value_of_default_column_.empty());
Slice wide_columns_copy = wide_columns_slice;
const Status s = WideColumnSerialization::GetValueOfDefaultColumn(
wide_columns_copy, value_of_default_column_);
if (!s.ok()) {
status_ = s;
valid_ = false;
return false;
}
is_wide_ = 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;
assert(!is_blob_);
assert(blob_value_.empty());
assert(!is_wide_);
assert(value_of_default_column_.empty());
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_);
if (ikey_.type == kTypeBlobIndex) {
if (!SetBlobValueIfNeeded(ikey_.user_key, iter_.value())) {
return false;
}
} else if (ikey_.type == kTypeWideColumnEntity) {
if (!SetWideColumnValueIfNeeded(iter_.value())) {
return false;
}
}
valid_ = true;
return true;
} 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;
}
} else if (ikey_.type == kTypeWideColumnEntity) {
if (!SetWideColumnValueIfNeeded(iter_.value())) {
return false;
}
}
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_.Equal(ikey.user_key, saved_key_.GetUserKey())) {
// hit the next user key, stop right here
break;
}
if (kTypeDeletion == ikey.type || kTypeSingleDeletion == 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();
Status s = Merge(&val, ikey.user_key);
if (!s.ok()) {
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;
const Slice blob_value = value();
Status s = Merge(&blob_value, ikey.user_key);
if (!s.ok()) {
return false;
}
ResetBlobValue();
assert(!is_wide_);
assert(value_of_default_column_.empty());
// iter_ is positioned after put
iter_.Next();
if (!iter_.status().ok()) {
valid_ = false;
return false;
}
return true;
} else if (kTypeWideColumnEntity == ikey.type) {
// TODO: support wide-column entities
status_ = Status::NotSupported(
"Merge currently not supported for wide-column entities");
valid_ = false;
return false;
} 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.
Status s = Merge(nullptr, saved_key_.GetUserKey());
if (!s.ok()) {
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();
ResetWideColumnValue();
ResetInternalKeysSkippedCounter();
bool ok = true;
if (direction_ == kForward) {
if (!ReverseToBackward()) {
ok = false;
}
}
if (ok) {
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();
assert(!is_blob_);
assert(blob_value_.empty());
assert(!is_wide_);
assert(value_of_default_column_.empty());
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) {
s = Merge(nullptr, saved_key_.GetUserKey());
if (!s.ok()) {
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;
const Slice blob_value = value();
s = Merge(&blob_value, saved_key_.GetUserKey());
if (!s.ok()) {
return false;
}
ResetBlobValue();
assert(!is_wide_);
assert(value_of_default_column_.empty());
return true;
} else if (last_not_merge_type == kTypeWideColumnEntity) {
// TODO: support wide-column entities
status_ = Status::NotSupported(
"Merge currently not supported for wide-column entities");
valid_ = false;
return false;
} else {
assert(last_not_merge_type == kTypeValue);
s = Merge(&pinned_value_, saved_key_.GetUserKey());
if (!s.ok()) {
return false;
}
return true;
}
break;
case kTypeValue:
// do nothing - we've already has value in pinned_value_
if (timestamp_lb_ != nullptr) {
saved_key_.SetInternalKey(saved_ikey_);
}
break;
case kTypeBlobIndex:
if (!SetBlobValueIfNeeded(saved_key_.GetUserKey(), pinned_value_)) {
return false;
}
break;
case kTypeWideColumnEntity:
if (!SetWideColumnValueIfNeeded(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;
assert(!is_blob_);
assert(blob_value_.empty());
assert(!is_wide_);
assert(value_of_default_column_.empty());
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;
}
} else if (ikey_.type == kTypeWideColumnEntity) {
if (!SetWideColumnValueIfNeeded(pinned_value_)) {
return false;
}
}
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_.Equal(ikey.user_key, saved_key_.GetUserKey())) {
break;
}
if (ikey.type == kTypeDeletion || ikey.type == kTypeSingleDeletion) {
break;
}
if (!iter_.PrepareValue()) {
valid_ = false;
return false;
}
if (ikey.type == kTypeValue) {
const Slice val = iter_.value();
Status s = Merge(&val, saved_key_.GetUserKey());
if (!s.ok()) {
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;
const Slice blob_value = value();
Status s = Merge(&blob_value, saved_key_.GetUserKey());
if (!s.ok()) {
return false;
}
ResetBlobValue();
assert(!is_wide_);
assert(value_of_default_column_.empty());
return true;
} else if (ikey.type == kTypeWideColumnEntity) {
// TODO: support wide-column entities
status_ = Status::NotSupported(
"Merge currently not supported for wide-column entities");
valid_ = false;
return false;
} else {
valid_ = false;
status_ = Status::Corruption(
"Unknown value type: " +
std::to_string(static_cast<unsigned int>(ikey.type)));
return false;
}
}
Status s = Merge(nullptr, saved_key_.GetUserKey());
if (!s.ok()) {
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;
}
Status 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_, true);
if (!s.ok()) {
valid_ = false;
status_ = s;
return s;
}
valid_ = true;
return s;
}
// 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();
ResetWideColumnValue();
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();
ResetWideColumnValue();
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();
ResetWideColumnValue();
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();
ResetWideColumnValue();
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();
ResetWideColumnValue();
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
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