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Delay write rate based on current CF state #281

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Dec 20, 2022
Merged

Delay write rate based on current CF state #281

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176 changes: 154 additions & 22 deletions db/column_family.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -881,6 +881,39 @@ int GetL0ThresholdSpeedupCompaction(int level0_file_num_compaction_trigger,
}
} // namespace

namespace {
const uint64_t Gb = 1ull << 30;
const uint64_t Mb = 1ull << 20;
const uint64_t kMinWriteRate = 16 * 1024u; // Minimum write rate 16KB/s.
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const int kMemtablePenalty = 10;
} // namespace

double ColumnFamilyData::TEST_CalculateWriteDelayDivider(
uint64_t compaction_needed_bytes,
const MutableCFOptions& mutable_cf_options,
WriteStallCause& write_stall_cause) {
return CalculateWriteDelayDividerAndMaybeUpdateWriteStallCause(
compaction_needed_bytes, mutable_cf_options, write_stall_cause);
}

std::unique_ptr<WriteControllerToken> ColumnFamilyData::DynamicSetupDelay(
WriteController* write_controller, uint64_t compaction_needed_bytes,
const MutableCFOptions& mutable_cf_options,
WriteStallCause& write_stall_cause) {
uint64_t max_write_rate = write_controller->max_delayed_write_rate();

const double rate_divider =
CalculateWriteDelayDividerAndMaybeUpdateWriteStallCause(
compaction_needed_bytes, mutable_cf_options, write_stall_cause);
assert(rate_divider >= 1);
auto write_rate = static_cast<uint64_t>(max_write_rate / rate_divider);
if (write_rate < kMinWriteRate) {
write_rate = kMinWriteRate;
}

return write_controller->GetDelayToken(write_rate);
}

std::pair<WriteStallCondition, ColumnFamilyData::WriteStallCause>
ColumnFamilyData::GetWriteStallConditionAndCause(
int num_unflushed_memtables, int num_l0_files,
Expand Down Expand Up @@ -919,6 +952,86 @@ ColumnFamilyData::GetWriteStallConditionAndCause(
return {WriteStallCondition::kNormal, WriteStallCause::kNone};
}

// Delay divider is by how much we divide the users delayed_write_rate.
// E.g. divider 10 will result in 10 Mb/s from users 100 Mb/s.
// The rate is reduced linearly according to the range from slowdown to stop.
double
ColumnFamilyData::CalculateWriteDelayDividerAndMaybeUpdateWriteStallCause(
uint64_t compaction_needed_bytes,
const MutableCFOptions& mutable_cf_options,
ColumnFamilyData::WriteStallCause& write_stall_cause) {
assert(current_ != nullptr);

const auto* vstorage = current_->storage_info();

// Memtables
// this can only be entered when we're at the last memtable and theres more
// than 3. delay by 10X when writing to the last memtable.
double memtable_divider = 1;
auto num_unflushed_memtables = imm()->NumNotFlushed();
if (mutable_cf_options.max_write_buffer_number > 3 &&
num_unflushed_memtables >=
mutable_cf_options.max_write_buffer_number - 1 &&
num_unflushed_memtables - 1 >=
ioptions_.min_write_buffer_number_to_merge) {
memtable_divider = kMemtablePenalty;
}

// Pending Compaction Bytes
double pending_divider = 1;
auto soft_limit = mutable_cf_options.soft_pending_compaction_bytes_limit;
if (soft_limit > 0 && compaction_needed_bytes >= soft_limit) {
auto hard_limit = mutable_cf_options.hard_pending_compaction_bytes_limit;
// soft_limit != hard_limit here. we're in a kDelayed state here and not
// stop.
assert(hard_limit > soft_limit);
uint64_t soft_hard_range = hard_limit - soft_limit;
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// change rate every 1G change or 100Mb if soft_hard_range is too small.
auto step_size = soft_hard_range > Gb ? Gb : 100 * Mb;
uint64_t num_steps = soft_hard_range / step_size;
auto extra_bytes = compaction_needed_bytes - soft_limit;
auto step_num = static_cast<uint64_t>(extra_bytes / step_size);
assert(step_num < num_steps);
if (num_steps > 0) {
pending_divider = 1 / (1 - (static_cast<double>(step_num) / num_steps));
}
}

double biggest_divider = 1;
if (memtable_divider > pending_divider) {
biggest_divider = memtable_divider;
write_stall_cause = WriteStallCause::kMemtableLimit;
} else if (pending_divider > 1) {
biggest_divider = pending_divider;
write_stall_cause = WriteStallCause::kPendingCompactionBytes;
}

// dont delay based on L0 when the user disables auto compactions
if (mutable_cf_options.disable_auto_compactions) {
return biggest_divider;
}

// L0 files
double l0_divider = 1;
const auto extra_l0_ssts = vstorage->NumLevelFiles(0) -
mutable_cf_options.level0_slowdown_writes_trigger;
if (extra_l0_ssts > 0) {
const auto num_L0_steps = mutable_cf_options.level0_stop_writes_trigger -
mutable_cf_options.level0_slowdown_writes_trigger;
assert(num_L0_steps > 0);
// since extra_l0_ssts == num_L0_steps then we're in a stop condition.
assert(extra_l0_ssts < num_L0_steps);
l0_divider = 1 / (1 - (extra_l0_ssts / num_L0_steps));
}

if (l0_divider > biggest_divider) {
biggest_divider = l0_divider;
write_stall_cause = WriteStallCause::kL0FileCountLimit;
}

return biggest_divider;
}

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WriteStallCondition ColumnFamilyData::RecalculateWriteStallConditions(
const MutableCFOptions& mutable_cf_options) {
auto write_stall_condition = WriteStallCondition::kNormal;
Expand All @@ -937,6 +1050,18 @@ WriteStallCondition ColumnFamilyData::RecalculateWriteStallConditions(

bool was_stopped = write_controller->IsStopped();
bool needed_delay = write_controller->NeedsDelay();
bool dynamic_delay = write_controller->is_dynamic_delay();

// GetWriteStallConditionAndCause returns the first condition met, so its
// possible that a later condition will require a harder rate limiting.
// calculate all conditions with DynamicSetupDelay and reavaluate the
// write_stall_cause. this is only relevant in the kDelayed case.
if (dynamic_delay &&
write_stall_condition == WriteStallCondition::kDelayed) {
write_controller_token_ =
DynamicSetupDelay(write_controller, compaction_needed_bytes,
mutable_cf_options, write_stall_cause);
}

if (write_stall_condition == WriteStallCondition::kStopped &&
write_stall_cause == WriteStallCause::kMemtableLimit) {
Expand Down Expand Up @@ -971,10 +1096,12 @@ WriteStallCondition ColumnFamilyData::RecalculateWriteStallConditions(
name_.c_str(), compaction_needed_bytes);
} else if (write_stall_condition == WriteStallCondition::kDelayed &&
write_stall_cause == WriteStallCause::kMemtableLimit) {
write_controller_token_ =
SetupDelay(write_controller, compaction_needed_bytes,
prev_compaction_needed_bytes_, was_stopped,
mutable_cf_options.disable_auto_compactions);
if (!dynamic_delay) {
write_controller_token_ =
SetupDelay(write_controller, compaction_needed_bytes,
prev_compaction_needed_bytes_, was_stopped,
mutable_cf_options.disable_auto_compactions);
}
internal_stats_->AddCFStats(InternalStats::MEMTABLE_LIMIT_SLOWDOWNS, 1);
ROCKS_LOG_WARN(
ioptions_.logger,
Expand All @@ -986,13 +1113,15 @@ WriteStallCondition ColumnFamilyData::RecalculateWriteStallConditions(
write_controller->delayed_write_rate());
} else if (write_stall_condition == WriteStallCondition::kDelayed &&
write_stall_cause == WriteStallCause::kL0FileCountLimit) {
// L0 is the last two files from stopping.
bool near_stop = vstorage->l0_delay_trigger_count() >=
mutable_cf_options.level0_stop_writes_trigger - 2;
write_controller_token_ =
SetupDelay(write_controller, compaction_needed_bytes,
prev_compaction_needed_bytes_, was_stopped || near_stop,
mutable_cf_options.disable_auto_compactions);
if (!dynamic_delay) {
// L0 is the last two files from stopping.
bool near_stop = vstorage->l0_delay_trigger_count() >=
mutable_cf_options.level0_stop_writes_trigger - 2;
write_controller_token_ =
SetupDelay(write_controller, compaction_needed_bytes,
prev_compaction_needed_bytes_, was_stopped || near_stop,
mutable_cf_options.disable_auto_compactions);
}
internal_stats_->AddCFStats(InternalStats::L0_FILE_COUNT_LIMIT_SLOWDOWNS,
1);
if (compaction_picker_->IsLevel0CompactionInProgress()) {
Expand All @@ -1009,18 +1138,21 @@ WriteStallCondition ColumnFamilyData::RecalculateWriteStallConditions(
// If the distance to hard limit is less than 1/4 of the gap between soft
// and
// hard bytes limit, we think it is near stop and speed up the slowdown.
bool near_stop =
mutable_cf_options.hard_pending_compaction_bytes_limit > 0 &&
(compaction_needed_bytes -
mutable_cf_options.soft_pending_compaction_bytes_limit) >
3 * (mutable_cf_options.hard_pending_compaction_bytes_limit -
mutable_cf_options.soft_pending_compaction_bytes_limit) /
4;
if (!dynamic_delay) {
bool near_stop =
mutable_cf_options.hard_pending_compaction_bytes_limit > 0 &&
(compaction_needed_bytes -
mutable_cf_options.soft_pending_compaction_bytes_limit) >
3 *
(mutable_cf_options.hard_pending_compaction_bytes_limit -
mutable_cf_options.soft_pending_compaction_bytes_limit) /
4;

write_controller_token_ =
SetupDelay(write_controller, compaction_needed_bytes,
prev_compaction_needed_bytes_, was_stopped || near_stop,
mutable_cf_options.disable_auto_compactions);
write_controller_token_ =
SetupDelay(write_controller, compaction_needed_bytes,
prev_compaction_needed_bytes_, was_stopped || near_stop,
mutable_cf_options.disable_auto_compactions);
}
internal_stats_->AddCFStats(
InternalStats::PENDING_COMPACTION_BYTES_LIMIT_SLOWDOWNS, 1);
ROCKS_LOG_WARN(
Expand Down
18 changes: 18 additions & 0 deletions db/column_family.h
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Original file line number Diff line number Diff line change
Expand Up @@ -485,6 +485,24 @@ class ColumnFamilyData {
WriteStallCondition RecalculateWriteStallConditions(
const MutableCFOptions& mutable_cf_options);

// REQUIREMENT: db mutex must be held
double TEST_CalculateWriteDelayDivider(
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uint64_t compaction_needed_bytes,
const MutableCFOptions& mutable_cf_options,
WriteStallCause& write_stall_cause);

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private:
std::unique_ptr<WriteControllerToken> DynamicSetupDelay(
WriteController* write_controller, uint64_t compaction_needed_bytes,
const MutableCFOptions& mutable_cf_options,
WriteStallCause& write_stall_cause);

double CalculateWriteDelayDividerAndMaybeUpdateWriteStallCause(
uint64_t compaction_needed_bytes,
const MutableCFOptions& mutable_cf_options,
WriteStallCause& write_stall_cause);

public:
void set_initialized() { initialized_.store(true); }

bool initialized() const { return initialized_.load(); }
Expand Down
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