rocksdb/db/write_controller_test.cc
Peter Dillinger e7a60d01b2 Revamp WriteController (#8064)
Summary:
WriteController had a number of issues:
* It could introduce a delay of 1ms even if the write rate never exceeded the
configured delayed_write_rate.
* The DB-wide delayed_write_rate could be exceeded in a number of ways
with multiple column families:
  * Wiping all pending delay "debts" when another column family joins
  the delay with GetDelayToken().
  * Resetting last_refill_time_ to (now + sleep amount) means each
  column family can write with delayed_write_rate for large writes.
  * Updating bytes_left_ for a partial refill without updating
  last_refill_time_ would essentially give out random bonuses,
  especially to medium-sized writes.

Now the code is much simpler, with these issues fixed. See comments in
the new code and new (replacement) tests.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8064

Test Plan: new tests, better than old tests

Reviewed By: mrambacher

Differential Revision: D27064936

Pulled By: pdillinger

fbshipit-source-id: 497c23fe6819340b8f3d440bd634d8a2bc47323f
2021-03-18 09:47:31 -07:00

248 lines
8.7 KiB
C++

// 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).
//
#include "db/write_controller.h"
#include <array>
#include <ratio>
#include "rocksdb/system_clock.h"
#include "test_util/testharness.h"
namespace ROCKSDB_NAMESPACE {
namespace {
class TimeSetClock : public SystemClockWrapper {
public:
explicit TimeSetClock() : SystemClockWrapper(nullptr) {}
const char* Name() const override { return "TimeSetClock"; }
uint64_t now_micros_ = 6666;
uint64_t NowNanos() override { return now_micros_ * std::milli::den; }
};
} // namespace
class WriteControllerTest : public testing::Test {
public:
WriteControllerTest() { clock_ = std::make_shared<TimeSetClock>(); }
std::shared_ptr<TimeSetClock> clock_;
};
// Make tests easier to read
#define MILLION *1000000u
#define MB MILLION
#define MBPS MILLION
#define SECS MILLION // in microseconds
TEST_F(WriteControllerTest, BasicAPI) {
WriteController controller(40 MBPS); // also set max delayed rate
EXPECT_EQ(controller.delayed_write_rate(), 40 MBPS);
EXPECT_FALSE(controller.IsStopped());
EXPECT_FALSE(controller.NeedsDelay());
EXPECT_EQ(0, controller.GetDelay(clock_.get(), 100 MB));
// set, get
controller.set_delayed_write_rate(20 MBPS);
EXPECT_EQ(controller.delayed_write_rate(), 20 MBPS);
EXPECT_FALSE(controller.IsStopped());
EXPECT_FALSE(controller.NeedsDelay());
EXPECT_EQ(0, controller.GetDelay(clock_.get(), 100 MB));
{
// set with token, get
auto delay_token_0 = controller.GetDelayToken(10 MBPS);
EXPECT_EQ(controller.delayed_write_rate(), 10 MBPS);
EXPECT_FALSE(controller.IsStopped());
EXPECT_TRUE(controller.NeedsDelay());
// test with delay
EXPECT_EQ(2 SECS, controller.GetDelay(clock_.get(), 20 MB));
clock_->now_micros_ += 2 SECS; // pay the "debt"
auto delay_token_1 = controller.GetDelayToken(2 MBPS);
EXPECT_EQ(10 SECS, controller.GetDelay(clock_.get(), 20 MB));
clock_->now_micros_ += 10 SECS; // pay the "debt"
auto delay_token_2 = controller.GetDelayToken(1 MBPS);
EXPECT_EQ(20 SECS, controller.GetDelay(clock_.get(), 20 MB));
clock_->now_micros_ += 20 SECS; // pay the "debt"
auto delay_token_3 = controller.GetDelayToken(20 MBPS);
EXPECT_EQ(1 SECS, controller.GetDelay(clock_.get(), 20 MB));
clock_->now_micros_ += 1 SECS; // pay the "debt"
// 60M is more than the max rate of 40M. Max rate will be used.
EXPECT_EQ(controller.delayed_write_rate(), 20 MBPS);
auto delay_token_4 =
controller.GetDelayToken(controller.delayed_write_rate() * 3);
EXPECT_EQ(controller.delayed_write_rate(), 40 MBPS);
EXPECT_EQ(static_cast<uint64_t>(0.5 SECS),
controller.GetDelay(clock_.get(), 20 MB));
EXPECT_FALSE(controller.IsStopped());
EXPECT_TRUE(controller.NeedsDelay());
// Test stop tokens
{
auto stop_token_1 = controller.GetStopToken();
EXPECT_TRUE(controller.IsStopped());
EXPECT_EQ(0, controller.GetDelay(clock_.get(), 100 MB));
{
auto stop_token_2 = controller.GetStopToken();
EXPECT_TRUE(controller.IsStopped());
EXPECT_EQ(0, controller.GetDelay(clock_.get(), 100 MB));
}
EXPECT_TRUE(controller.IsStopped());
EXPECT_EQ(0, controller.GetDelay(clock_.get(), 100 MB));
}
// Stop tokens released
EXPECT_FALSE(controller.IsStopped());
EXPECT_TRUE(controller.NeedsDelay());
EXPECT_EQ(controller.delayed_write_rate(), 40 MBPS);
// pay the previous "debt"
clock_->now_micros_ += static_cast<uint64_t>(0.5 SECS);
EXPECT_EQ(1 SECS, controller.GetDelay(clock_.get(), 40 MB));
}
// Delay tokens released
EXPECT_FALSE(controller.NeedsDelay());
}
TEST_F(WriteControllerTest, StartFilled) {
WriteController controller(10 MBPS);
// Attempt to write two things that combined would be allowed within
// a single refill interval
auto delay_token_0 =
controller.GetDelayToken(controller.delayed_write_rate());
// Verify no delay because write rate has not been exceeded within
// refill interval.
EXPECT_EQ(0U, controller.GetDelay(clock_.get(), 2000u /*bytes*/));
EXPECT_EQ(0U, controller.GetDelay(clock_.get(), 2000u /*bytes*/));
// Allow refill (kMicrosPerRefill)
clock_->now_micros_ += 1000;
// Again
EXPECT_EQ(0U, controller.GetDelay(clock_.get(), 2000u /*bytes*/));
EXPECT_EQ(0U, controller.GetDelay(clock_.get(), 2000u /*bytes*/));
// Control: something bigger that would exceed write rate within interval
uint64_t delay = controller.GetDelay(clock_.get(), 10 MB);
EXPECT_GT(1.0 * delay, 0.999 SECS);
EXPECT_LT(1.0 * delay, 1.001 SECS);
}
TEST_F(WriteControllerTest, DebtAccumulation) {
WriteController controller(10 MBPS);
std::array<std::unique_ptr<WriteControllerToken>, 10> tokens;
// Accumulate a time delay debt with no passage of time, like many column
// families delaying writes simultaneously. (Old versions of WriteController
// would reset the debt on every GetDelayToken.)
uint64_t debt = 0;
for (unsigned i = 0; i < tokens.size(); ++i) {
tokens[i] = controller.GetDelayToken((i + 1u) MBPS);
uint64_t delay = controller.GetDelay(clock_.get(), 63 MB);
ASSERT_GT(delay, debt);
uint64_t incremental = delay - debt;
ASSERT_EQ(incremental, (63 SECS) / (i + 1u));
debt += incremental;
}
// Pay down the debt
clock_->now_micros_ += debt;
debt = 0;
// Now accumulate debt with some passage of time.
for (unsigned i = 0; i < tokens.size(); ++i) {
// Debt is accumulated in time, not in bytes, so this new write
// limit is not applied to prior requested delays, even it they are
// in progress.
tokens[i] = controller.GetDelayToken((i + 1u) MBPS);
uint64_t delay = controller.GetDelay(clock_.get(), 63 MB);
ASSERT_GT(delay, debt);
uint64_t incremental = delay - debt;
ASSERT_EQ(incremental, (63 SECS) / (i + 1u));
debt += incremental;
uint64_t credit = debt / 2;
clock_->now_micros_ += credit;
debt -= credit;
}
// Pay down the debt
clock_->now_micros_ += debt;
debt = 0; // consistent state
(void)debt; // appease clang-analyze
// Verify paid down
EXPECT_EQ(0U, controller.GetDelay(clock_.get(), 100u /*small bytes*/));
// Accumulate another debt, without accounting, and releasing tokens
for (unsigned i = 0; i < tokens.size(); ++i) {
// Big and small are delayed
ASSERT_LT(0U, controller.GetDelay(clock_.get(), 63 MB));
ASSERT_LT(0U, controller.GetDelay(clock_.get(), 100u /*small bytes*/));
tokens[i].reset();
}
// All tokens released.
// Verify that releasing all tokens pays down debt, even with no time passage.
tokens[0] = controller.GetDelayToken(1 MBPS);
ASSERT_EQ(0U, controller.GetDelay(clock_.get(), 100u /*small bytes*/));
}
// This may or may not be a "good" feature, but it's an old feature
TEST_F(WriteControllerTest, CreditAccumulation) {
WriteController controller(10 MBPS);
std::array<std::unique_ptr<WriteControllerToken>, 10> tokens;
// Ensure started
tokens[0] = controller.GetDelayToken(1 MBPS);
ASSERT_EQ(10 SECS, controller.GetDelay(clock_.get(), 10 MB));
clock_->now_micros_ += 10 SECS;
// Accumulate a credit
uint64_t credit = 1000 SECS /* see below: * 1 MB / 1 SEC */;
clock_->now_micros_ += credit;
// Spend some credit (burst of I/O)
for (unsigned i = 0; i < tokens.size(); ++i) {
tokens[i] = controller.GetDelayToken((i + 1u) MBPS);
ASSERT_EQ(0U, controller.GetDelay(clock_.get(), 63 MB));
// In WriteController, credit is accumulated in bytes, not in time.
// After an "unnecessary" delay, all of our time credit will be
// translated to bytes on the next operation, in this case with
// setting 1 MBPS. So regardless of the rate at delay time, we just
// account for the bytes.
credit -= 63 MB;
}
// Spend remaining credit
tokens[0] = controller.GetDelayToken(1 MBPS);
ASSERT_EQ(0U, controller.GetDelay(clock_.get(), credit));
// Verify
ASSERT_EQ(10 SECS, controller.GetDelay(clock_.get(), 10 MB));
clock_->now_micros_ += 10 SECS;
// Accumulate a credit, no accounting
clock_->now_micros_ += 1000 SECS;
// Spend a small amount, releasing tokens
for (unsigned i = 0; i < tokens.size(); ++i) {
ASSERT_EQ(0U, controller.GetDelay(clock_.get(), 3 MB));
tokens[i].reset();
}
// All tokens released.
// Verify credit is wiped away on new delay.
tokens[0] = controller.GetDelayToken(1 MBPS);
ASSERT_EQ(10 SECS, controller.GetDelay(clock_.get(), 10 MB));
}
} // namespace ROCKSDB_NAMESPACE
int main(int argc, char** argv) {
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}