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rocksdb/db/seqno_to_time_mapping.cc

325 lines
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// Copyright (c) Meta Platforms, Inc. and affiliates.
//
// 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).
#include "db/seqno_to_time_mapping.h"
#include "db/version_edit.h"
#include "util/string_util.h"
namespace ROCKSDB_NAMESPACE {
uint64_t SeqnoToTimeMapping::GetOldestApproximateTime(
const SequenceNumber seqno) const {
assert(is_sorted_);
auto it = std::upper_bound(seqno_time_mapping_.begin(),
seqno_time_mapping_.end(), seqno);
if (it == seqno_time_mapping_.begin()) {
return 0;
}
it--;
return it->time;
}
void SeqnoToTimeMapping::Add(SequenceNumber seqno, uint64_t time) {
if (seqno == 0) {
return;
}
is_sorted_ = false;
seqno_time_mapping_.emplace_back(seqno, time);
}
SequenceNumber SeqnoToTimeMapping::TruncateOldEntries(const uint64_t now) {
assert(is_sorted_);
if (max_time_duration_ == 0) {
return 0;
}
const uint64_t cut_off_time =
now > max_time_duration_ ? now - max_time_duration_ : 0;
assert(cut_off_time <= now); // no overflow
auto it = std::upper_bound(
seqno_time_mapping_.begin(), seqno_time_mapping_.end(), cut_off_time,
[](uint64_t target, const SeqnoTimePair& other) -> bool {
return target < other.time;
});
if (it == seqno_time_mapping_.begin()) {
return 0;
}
it--;
seqno_time_mapping_.erase(seqno_time_mapping_.begin(), it);
return seqno_time_mapping_.front().seqno;
}
// The encoded format is:
// [num_of_entries][[seqno][time],[seqno][time],...]
// ^ ^
// var_int delta_encoded (var_int)
void SeqnoToTimeMapping::Encode(std::string& dest, const SequenceNumber start,
const SequenceNumber end, const uint64_t now,
const uint64_t output_size) const {
assert(is_sorted_);
if (start > end) {
// It could happen when the SST file is empty, the initial value of min
// sequence number is kMaxSequenceNumber and max is 0.
// The empty output file will be removed in the final step of compaction.
return;
}
auto start_it = std::upper_bound(seqno_time_mapping_.begin(),
seqno_time_mapping_.end(), start);
if (start_it != seqno_time_mapping_.begin()) {
start_it--;
}
auto end_it = std::upper_bound(seqno_time_mapping_.begin(),
seqno_time_mapping_.end(), end);
if (end_it == seqno_time_mapping_.begin()) {
return;
}
if (start_it >= end_it) {
return;
}
// truncate old entries that are not needed
if (max_time_duration_ > 0) {
const uint64_t cut_off_time =
now > max_time_duration_ ? now - max_time_duration_ : 0;
while (start_it < end_it && start_it->time < cut_off_time) {
start_it++;
}
}
// If there are more data than needed, pick the entries for encoding.
// It's not the most optimized algorithm for selecting the best representative
// entries over the time.
// It starts from the beginning and makes sure the distance is larger than
// `(end - start) / size` before selecting the number. For example, for the
// following list, pick 3 entries (it will pick seqno #1, #6, #8):
// 1 -> 10
// 5 -> 17
// 6 -> 25
// 8 -> 30
// first, it always picks the first one, then there are 2 num_entries_to_fill
// and the time difference between current one vs. the last one is
// (30 - 10) = 20. 20/2 = 10. So it will skip until 10+10 = 20. => it skips
// #5 and pick #6.
// But the most optimized solution is picking #1 #5 #8, as it will be more
// evenly distributed for time. Anyway the following algorithm is simple and
// may over-select new data, which is good. We do want more accurate time
// information for recent data.
std::deque<SeqnoTimePair> output_copy;
if (std::distance(start_it, end_it) > static_cast<int64_t>(output_size)) {
int64_t num_entries_to_fill = static_cast<int64_t>(output_size);
auto last_it = end_it;
last_it--;
uint64_t end_time = last_it->time;
uint64_t skip_until_time = 0;
for (auto it = start_it; it < end_it; it++) {
// skip if it's not reach the skip_until_time yet
if (std::distance(it, end_it) > num_entries_to_fill &&
it->time < skip_until_time) {
continue;
}
output_copy.push_back(*it);
num_entries_to_fill--;
if (std::distance(it, end_it) > num_entries_to_fill &&
num_entries_to_fill > 0) {
// If there are more entries than we need, re-calculate the
// skip_until_time, which means skip until that time
skip_until_time =
it->time + ((end_time - it->time) / num_entries_to_fill);
}
}
// Make sure all entries are filled
assert(num_entries_to_fill == 0);
start_it = output_copy.begin();
end_it = output_copy.end();
}
// Delta encode the data
uint64_t size = std::distance(start_it, end_it);
PutVarint64(&dest, size);
SeqnoTimePair base;
for (auto it = start_it; it < end_it; it++) {
assert(base < *it);
SeqnoTimePair val = *it - base;
base = *it;
val.Encode(dest);
}
}
Status SeqnoToTimeMapping::Add(const std::string& seqno_time_mapping_str) {
Slice input(seqno_time_mapping_str);
if (input.empty()) {
return Status::OK();
}
uint64_t size;
if (!GetVarint64(&input, &size)) {
return Status::Corruption("Invalid sequence number time size");
}
is_sorted_ = false;
SeqnoTimePair base;
for (uint64_t i = 0; i < size; i++) {
SeqnoTimePair val;
Status s = val.Decode(input);
if (!s.ok()) {
return s;
}
val.Add(base);
seqno_time_mapping_.emplace_back(val);
base = val;
}
return Status::OK();
}
void SeqnoToTimeMapping::SeqnoTimePair::Encode(std::string& dest) const {
PutVarint64Varint64(&dest, seqno, time);
}
Status SeqnoToTimeMapping::SeqnoTimePair::Decode(Slice& input) {
if (!GetVarint64(&input, &seqno)) {
return Status::Corruption("Invalid sequence number");
}
if (!GetVarint64(&input, &time)) {
return Status::Corruption("Invalid time");
}
return Status::OK();
}
bool SeqnoToTimeMapping::Append(SequenceNumber seqno, uint64_t time) {
assert(is_sorted_);
// skip seq number 0, which may have special meaning, like zeroed out data
if (seqno == 0) {
return false;
}
if (!Empty()) {
if (seqno < Last().seqno || time < Last().time) {
return false;
}
if (seqno == Last().seqno) {
Last().time = time;
return true;
}
if (time == Last().time) {
// new sequence has the same time as old one, no need to add new mapping
return false;
}
}
seqno_time_mapping_.emplace_back(seqno, time);
if (seqno_time_mapping_.size() > max_capacity_) {
seqno_time_mapping_.pop_front();
}
return true;
}
bool SeqnoToTimeMapping::Resize(uint64_t min_time_duration,
uint64_t max_time_duration) {
uint64_t new_max_capacity =
CalculateMaxCapacity(min_time_duration, max_time_duration);
if (new_max_capacity == max_capacity_) {
return false;
} else if (new_max_capacity < seqno_time_mapping_.size()) {
uint64_t delta = seqno_time_mapping_.size() - new_max_capacity;
seqno_time_mapping_.erase(seqno_time_mapping_.begin(),
seqno_time_mapping_.begin() + delta);
}
max_capacity_ = new_max_capacity;
return true;
}
Status SeqnoToTimeMapping::Sort() {
if (is_sorted_) {
return Status::OK();
}
if (seqno_time_mapping_.empty()) {
is_sorted_ = true;
return Status::OK();
}
std::deque<SeqnoTimePair> copy = std::move(seqno_time_mapping_);
std::sort(copy.begin(), copy.end());
seqno_time_mapping_.clear();
// remove seqno = 0, which may have special meaning, like zeroed out data
while (copy.front().seqno == 0) {
copy.pop_front();
}
SeqnoTimePair prev = copy.front();
for (const auto& it : copy) {
// If sequence number is the same, pick the one with larger time, which is
// more accurate than the older time.
if (it.seqno == prev.seqno) {
assert(it.time >= prev.time);
prev.time = it.time;
} else {
assert(it.seqno > prev.seqno);
// If a larger sequence number has an older time which is not useful, skip
if (it.time > prev.time) {
seqno_time_mapping_.push_back(prev);
prev = it;
}
}
}
seqno_time_mapping_.emplace_back(prev);
is_sorted_ = true;
return Status::OK();
}
std::string SeqnoToTimeMapping::ToHumanString() const {
std::string ret;
for (const auto& seq_time : seqno_time_mapping_) {
AppendNumberTo(&ret, seq_time.seqno);
ret.append("->");
AppendNumberTo(&ret, seq_time.time);
ret.append(",");
}
return ret;
}
SeqnoToTimeMapping SeqnoToTimeMapping::Copy(
SequenceNumber smallest_seqno) const {
SeqnoToTimeMapping ret;
auto it = std::upper_bound(seqno_time_mapping_.begin(),
seqno_time_mapping_.end(), smallest_seqno);
if (it != seqno_time_mapping_.begin()) {
it--;
}
std::copy(it, seqno_time_mapping_.end(),
std::back_inserter(ret.seqno_time_mapping_));
return ret;
}
uint64_t SeqnoToTimeMapping::CalculateMaxCapacity(uint64_t min_time_duration,
uint64_t max_time_duration) {
if (min_time_duration == 0) {
return 0;
}
return std::min(
kMaxSeqnoToTimeEntries,
max_time_duration * kMaxSeqnoTimePairsPerCF / min_time_duration);
}
SeqnoToTimeMapping::SeqnoTimePair SeqnoToTimeMapping::SeqnoTimePair::operator-(
const SeqnoTimePair& other) const {
SeqnoTimePair res;
res.seqno = seqno - other.seqno;
res.time = time - other.time;
return res;
}
} // namespace ROCKSDB_NAMESPACE