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Slowdown when writing to the last write buffer

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Summary: Now if inserting to mem table is much faster than writing to files, there is no mechanism users can rely on to avoid stopping for reaching options.max_write_buffer_number. With the commit, if there are more than four maximum write buffers configured, we slow down to the rate of options.delayed_write_rate while we reach the last one.

Test Plan:
1. Add a new unit test.
2. Run db_bench with

./db_bench --benchmarks=fillrandom --num=10000000 --max_background_flushes=6 --batch_size=32 -max_write_buffer_number=4 --delayed_write_rate=500000 --statistics

based on hard drive and see stopping is avoided with the commit.

Reviewers: yhchiang, IslamAbdelRahman, anthony, rven, kradhakrishnan, igor

Reviewed By: igor

Subscribers: MarkCallaghan, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D52047
This commit is contained in:
sdong 2015-12-16 17:08:09 -08:00
parent 6b2a3ac92c
commit d72b31774e
6 changed files with 56 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
HISTORY.md
View File

@ -4,6 +4,7 @@
### Public API Changes
* Change names in CompactionPri and add a new one.
* Deprecate options.soft_rate_limit and add options.soft_pending_compaction_bytes_limit.
* If options.max_write_buffer_number > 3, writes will be slowed down when writing to the last write buffer to delay a full stop.
## 4.3.0 (12/8/2015)
### New Features

10
db/column_family.cc
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@ -447,6 +447,16 @@ void ColumnFamilyData::RecalculateWriteStallConditions(
"(waiting for flush), max_write_buffer_number is set to %d",
name_.c_str(), imm()->NumNotFlushed(),
mutable_cf_options.max_write_buffer_number);
} else if (mutable_cf_options.max_write_buffer_number > 3 &&
imm()->NumNotFlushed() >=
mutable_cf_options.max_write_buffer_number - 1) {
write_controller_token_ = write_controller->GetDelayToken();
internal_stats_->AddCFStats(InternalStats::MEMTABLE_SLOWDOWN, 1);
Log(InfoLogLevel::WARN_LEVEL, ioptions_.info_log,
"[%s] Stalling writes because we have %d immutable memtables "
"(waiting for flush), max_write_buffer_number is set to %d",
name_.c_str(), imm()->NumNotFlushed(),
mutable_cf_options.max_write_buffer_number);
} else if (vstorage->l0_delay_trigger_count() >=
mutable_cf_options.level0_stop_writes_trigger) {
write_controller_token_ = write_controller->GetStopToken();

36
db/db_test.cc
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@ -9144,6 +9144,42 @@ TEST_F(DBTest, SoftLimit) {
sleeping_task_low.WakeUp();
sleeping_task_low.WaitUntilDone();
}
TEST_F(DBTest, LastWriteBufferDelay) {
Options options;
options.env = env_;
options = CurrentOptions(options);
options.write_buffer_size = 100000;
options.max_write_buffer_number = 4;
options.delayed_write_rate = 20000;
options.compression = kNoCompression;
options.disable_auto_compactions = true;
int kNumKeysPerMemtable = 3;
options.memtable_factory.reset(
new SpecialSkipListFactory(kNumKeysPerMemtable));
Reopen(options);
test::SleepingBackgroundTask sleeping_task;
// Block flushes
env_->Schedule(&test::SleepingBackgroundTask::DoSleepTask, &sleeping_task,
Env::Priority::HIGH);
sleeping_task.WaitUntilSleeping();
// Create 3 L0 files, making score of L0 to be 3.
for (int i = 0; i < 3; i++) {
// Fill one mem table
for (int j = 0; j < kNumKeysPerMemtable; j++) {
Put(Key(j), "");
}
ASSERT_TRUE(!dbfull()->TEST_write_controler().NeedsDelay());
}
// Inserting a new entry would create a new mem table, triggering slow down.
Put(Key(0), "");
ASSERT_TRUE(dbfull()->TEST_write_controler().NeedsDelay());
sleeping_task.WakeUp();
sleeping_task.WaitUntilDone();
}
#endif // ROCKSDB_LITE
TEST_F(DBTest, FailWhenCompressionNotSupportedTest) {

5
db/internal_stats.cc
View File

@ -700,7 +700,7 @@ void InternalStats::DumpCFStats(std::string* value) {
cf_stats_count_[LEVEL0_NUM_FILES_TOTAL] +
cf_stats_count_[SOFT_PENDING_COMPACTION_BYTES_LIMIT] +
cf_stats_count_[HARD_PENDING_COMPACTION_BYTES_LIMIT] +
cf_stats_count_[MEMTABLE_COMPACTION];
cf_stats_count_[MEMTABLE_COMPACTION] + cf_stats_count_[MEMTABLE_SLOWDOWN];
// Stats summary across levels
PrintLevelStats(buf, sizeof(buf), "Sum", total_files,
total_files_being_compacted, total_file_size, 0, w_amp,
@ -734,6 +734,8 @@ void InternalStats::DumpCFStats(std::string* value) {
" slowdown for pending_compaction_bytes, "
"%" PRIu64
" memtable_compaction, "
"%" PRIu64
" memtable_slowdown, "
"interval %" PRIu64 " total count\n",
cf_stats_count_[LEVEL0_SLOWDOWN_TOTAL],
cf_stats_count_[LEVEL0_SLOWDOWN_WITH_COMPACTION],
@ -742,6 +744,7 @@ void InternalStats::DumpCFStats(std::string* value) {
cf_stats_count_[HARD_PENDING_COMPACTION_BYTES_LIMIT],
cf_stats_count_[SOFT_PENDING_COMPACTION_BYTES_LIMIT],
cf_stats_count_[MEMTABLE_COMPACTION],
cf_stats_count_[MEMTABLE_SLOWDOWN],
total_stall_count - cf_stats_snapshot_.stall_count);
value->append(buf);

2
db/internal_stats.h
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@ -86,6 +86,7 @@ class InternalStats {
LEVEL0_SLOWDOWN_TOTAL,
LEVEL0_SLOWDOWN_WITH_COMPACTION,
MEMTABLE_COMPACTION,
MEMTABLE_SLOWDOWN,
LEVEL0_NUM_FILES_TOTAL,
LEVEL0_NUM_FILES_WITH_COMPACTION,
SOFT_PENDING_COMPACTION_BYTES_LIMIT,
@ -343,6 +344,7 @@ class InternalStats {
LEVEL0_SLOWDOWN_TOTAL,
LEVEL0_SLOWDOWN_WITH_COMPACTION,
MEMTABLE_COMPACTION,
MEMTABLE_SLOWDOWN,
LEVEL0_NUM_FILES_TOTAL,
LEVEL0_NUM_FILES_WITH_COMPACTION,
SOFT_PENDING_COMPACTION_BYTES_LIMIT,

3
include/rocksdb/options.h
View File

@ -256,6 +256,9 @@ struct ColumnFamilyOptions {
// The default and the minimum number is 2, so that when 1 write buffer
// is being flushed to storage, new writes can continue to the other
// write buffer.
// If max_write_buffer_number > 3, writing will be slowed down to
// options.delayed_write_rate if we are writing to the last write buffer
// allowed.
//
// Default: 2
//