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Improve RocksDB "get" performance by computing merge result in memtable

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Summary:
Added an option (max_successive_merges) that can be used to specify the
maximum number of successive merge operations on a key in the memtable.
This can be used to improve performance of the "get" operation. If many
successive merge operations are performed on a key, the performance of "get"
operations on the key deteriorates, as the value has to be computed for each
"get" operation by applying all the successive merge operations.

FB Task ID: #3428853

Test Plan:
make all check
db_bench --benchmarks=readrandommergerandom
counter_stress_test

Reviewers: haobo, vamsi, dhruba, sdong

Reviewed By: haobo

CC: zshao

Differential Revision: https://reviews.facebook.net/D14991
This commit is contained in:
Schalk-Willem Kruger 2014-01-10 17:33:56 -08:00
parent 62197d28b6
commit a09ee1069d
7 changed files with 320 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

97
db/db_bench.cc
View File

@ -94,6 +94,8 @@ DEFINE_string(benchmarks,
"\tmergerandom -- same as updaterandom/appendrandom using merge"
" operator. "
"Must be used with merge_operator\n"
"\treadrandommergerandom -- perform N random read-or-merge "
"operations. Must be used with merge_operator\n"
"\tseekrandom -- N random seeks\n"
"\tcrc32c -- repeated crc32c of 4K of data\n"
"\tacquireload -- load N*1000 times\n"
@ -112,6 +114,11 @@ DEFINE_int64(numdistinct, 1000,
"read/write on fewer keys so that gets are more likely to find the"
" key and puts are more likely to update the same key");
DEFINE_int64(merge_keys, -1,
"Number of distinct keys to use for MergeRandom and "
"ReadRandomMergeRandom. "
"If negative, there will be FLAGS_num keys.");
DEFINE_int64(reads, -1, "Number of read operations to do. "
"If negative, do FLAGS_num reads.");
@ -297,6 +304,11 @@ DEFINE_int32(readwritepercent, 90, "Ratio of reads to reads/writes (expressed"
"default value 90 means 90% operations out of all reads and writes"
" operations are reads. In other words, 9 gets for every 1 put.");
DEFINE_int32(mergereadpercent, 70, "Ratio of merges to merges&reads (expressed"
" as percentage) for the ReadRandomMergeRandom workload. The"
" default value 70 means 70% out of all read and merge operations"
" are merges. In other words, 7 merges for every 3 gets.");
DEFINE_int32(deletepercent, 2, "Percentage of deletes out of reads/writes/"
"deletes (used in RandomWithVerify only). RandomWithVerify "
"calculates writepercent as (100 - FLAGS_readwritepercent - "
@ -446,6 +458,9 @@ DEFINE_uint64(bytes_per_sync, rocksdb::Options().bytes_per_sync,
DEFINE_bool(filter_deletes, false, " On true, deletes use bloom-filter and drop"
" the delete if key not present");
DEFINE_int32(max_successive_merges, 0, "Maximum number of successive merge"
" operations on a key in the memtable");
static bool ValidatePrefixSize(const char* flagname, int32_t value) {
if (value < 0 || value>=2000000000) {
fprintf(stderr, "Invalid value for --%s: %d. 0<= PrefixSize <=2000000000\n",
@ -784,6 +799,7 @@ class Benchmark {
long long reads_;
long long writes_;
long long readwrites_;
long long merge_keys_;
int heap_counter_;
char keyFormat_[100]; // will contain the format of key. e.g "%016d"
void PrintHeader() {
@ -958,6 +974,7 @@ class Benchmark {
readwrites_((FLAGS_writes < 0 && FLAGS_reads < 0)? FLAGS_num :
((FLAGS_writes > FLAGS_reads) ? FLAGS_writes : FLAGS_reads)
),
merge_keys_(FLAGS_merge_keys < 0 ? FLAGS_num : FLAGS_merge_keys),
heap_counter_(0) {
std::vector<std::string> files;
FLAGS_env->GetChildren(FLAGS_db, &files);
@ -985,8 +1002,8 @@ class Benchmark {
}
unique_ptr<char []> GenerateKeyFromInt(long long v, const char* suffix = "") {
unique_ptr<char []> keyInStr(new char[kMaxKeySize]);
snprintf(keyInStr.get(), kMaxKeySize, keyFormat_, v, suffix);
unique_ptr<char []> keyInStr(new char[kMaxKeySize + 1]);
snprintf(keyInStr.get(), kMaxKeySize + 1, keyFormat_, v, suffix);
return keyInStr;
}
@ -1087,6 +1104,14 @@ class Benchmark {
method = &Benchmark::ReadWhileWriting;
} else if (name == Slice("readrandomwriterandom")) {
method = &Benchmark::ReadRandomWriteRandom;
} else if (name == Slice("readrandommergerandom")) {
if (FLAGS_merge_operator.empty()) {
fprintf(stdout, "%-12s : skipped (--merge_operator is unknown)\n",
name.ToString().c_str());
method = nullptr;
} else {
method = &Benchmark::ReadRandomMergeRandom;
}
} else if (name == Slice("updaterandom")) {
method = &Benchmark::UpdateRandom;
} else if (name == Slice("appendrandom")) {
@ -1421,6 +1446,7 @@ class Benchmark {
FLAGS_merge_operator.c_str());
exit(1);
}
options.max_successive_merges = FLAGS_max_successive_merges;
// set universal style compaction configurations, if applicable
if (FLAGS_universal_size_ratio != 0) {
@ -2375,13 +2401,16 @@ class Benchmark {
//
// For example, use FLAGS_merge_operator="uint64add" and FLAGS_value_size=8
// to simulate random additions over 64-bit integers using merge.
//
// The number of merges on the same key can be controlled by adjusting
// FLAGS_merge_keys.
void MergeRandom(ThreadState* thread) {
RandomGenerator gen;
// The number of iterations is the larger of read_ or write_
Duration duration(FLAGS_duration, readwrites_);
while (!duration.Done(1)) {
const long long k = thread->rand.Next() % FLAGS_num;
const long long k = thread->rand.Next() % merge_keys_;
unique_ptr<char []> key = GenerateKeyFromInt(k);
Status s = db_->Merge(write_options_, key.get(),
@ -2400,6 +2429,68 @@ class Benchmark {
thread->stats.AddMessage(msg);
}
// Read and merge random keys. The amount of reads and merges are controlled
// by adjusting FLAGS_num and FLAGS_mergereadpercent. The number of distinct
// keys (and thus also the number of reads and merges on the same key) can be
// adjusted with FLAGS_merge_keys.
//
// As with MergeRandom, the merge operator to use should be defined by
// FLAGS_merge_operator.
void ReadRandomMergeRandom(ThreadState* thread) {
ReadOptions options(FLAGS_verify_checksum, true);
RandomGenerator gen;
std::string value;
long long num_hits = 0;
long long num_gets = 0;
long long num_merges = 0;
size_t max_length = 0;
// the number of iterations is the larger of read_ or write_
Duration duration(FLAGS_duration, readwrites_);
while (!duration.Done(1)) {
const long long k = thread->rand.Next() % merge_keys_;
unique_ptr<char []> key = GenerateKeyFromInt(k);
bool do_merge = int(thread->rand.Next() % 100) < FLAGS_mergereadpercent;
if (do_merge) {
Status s = db_->Merge(write_options_, key.get(),
gen.Generate(value_size_));
if (!s.ok()) {
fprintf(stderr, "merge error: %s\n", s.ToString().c_str());
exit(1);
}
num_merges++;
} else {
Status s = db_->Get(options, key.get(), &value);
if (value.length() > max_length)
max_length = value.length();
if (!s.ok() && !s.IsNotFound()) {
fprintf(stderr, "get error: %s\n", s.ToString().c_str());
// we continue after error rather than exiting so that we can
// find more errors if any
} else if (!s.IsNotFound()) {
num_hits++;
}
num_gets++;
}
thread->stats.FinishedSingleOp(db_);
}
char msg[100];
snprintf(msg, sizeof(msg),
"(reads:%lld merges:%lld total:%lld hits:%lld maxlength:%zu)",
num_gets, num_merges, readwrites_, num_hits, max_length);
thread->stats.AddMessage(msg);
}
void Compact(ThreadState* thread) {
db_->CompactRange(nullptr, nullptr);
}

33
db/memtable.cc
View File

@ -326,4 +326,37 @@ bool MemTable::Update(SequenceNumber seq, ValueType type,
// Key doesn't exist
return false;
}
size_t MemTable::CountSuccessiveMergeEntries(const LookupKey& key) {
Slice memkey = key.memtable_key();
// A total ordered iterator is costly for some memtablerep (prefix aware
// reps). By passing in the user key, we allow efficient iterator creation.
// The iterator only needs to be ordered within the same user key.
std::shared_ptr<MemTableRep::Iterator> iter(
table_->GetIterator(key.user_key()));
iter->Seek(memkey.data());
size_t num_successive_merges = 0;
for (; iter->Valid(); iter->Next()) {
const char* entry = iter->key();
uint32_t key_length;
const char* iter_key_ptr = GetVarint32Ptr(entry, entry + 5, &key_length);
if (!comparator_.comparator.user_comparator()->Compare(
Slice(iter_key_ptr, key_length - 8), key.user_key()) == 0) {
break;
}
const uint64_t tag = DecodeFixed64(iter_key_ptr + key_length - 8);
if (static_cast<ValueType>(tag & 0xff) != kTypeMerge) {
break;
}
++num_successive_merges;
}
return num_successive_merges;
}
} // namespace rocksdb

5
db/memtable.h
View File

@ -107,6 +107,11 @@ class MemTable {
const Slice& key,
const Slice& value);
// Returns the number of successive merge entries starting from the newest
// entry for the key up to the last non-merge entry or last entry for the
// key in the memtable.
size_t CountSuccessiveMergeEntries(const LookupKey& key);
// Returns the edits area that is needed for flushing the memtable
VersionEdit* GetEdits() { return &edit_; }

118
db/merge_test.cc
View File

@ -14,6 +14,7 @@
#include "rocksdb/merge_operator.h"
#include "db/dbformat.h"
#include "db/db_impl.h"
#include "db/write_batch_internal.h"
#include "utilities/merge_operators.h"
#include "util/testharness.h"
#include "utilities/utility_db.h"
@ -21,13 +22,52 @@
using namespace std;
using namespace rocksdb;
namespace {
int numMergeOperatorCalls;
std::shared_ptr<DB> OpenDb(const string& dbname, const bool ttl = false) {
void resetNumMergeOperatorCalls() {
numMergeOperatorCalls = 0;
}
}
class CountMergeOperator : public AssociativeMergeOperator {
public:
CountMergeOperator() {
mergeOperator_ = MergeOperators::CreateUInt64AddOperator();
}
virtual bool Merge(const Slice& key,
const Slice* existing_value,
const Slice& value,
std::string* new_value,
Logger* logger) const override {
++numMergeOperatorCalls;
return mergeOperator_->PartialMerge(
key,
*existing_value,
value,
new_value,
logger);
}
virtual const char* Name() const override {
return "UInt64AddOperator";
}
private:
std::shared_ptr<MergeOperator> mergeOperator_;
};
std::shared_ptr<DB> OpenDb(
const string& dbname,
const bool ttl = false,
const unsigned max_successive_merges = 0) {
DB* db;
StackableDB* sdb;
Options options;
options.create_if_missing = true;
options.merge_operator = MergeOperators::CreateUInt64AddOperator();
options.merge_operator = std::make_shared<CountMergeOperator>();
options.max_successive_merges = max_successive_merges;
Status s;
DestroyDB(dbname, Options());
if (ttl) {
@ -243,6 +283,67 @@ void testCounters(Counters& counters, DB* db, bool test_compaction) {
}
}
void testSuccessiveMerge(
Counters& counters, int max_num_merges, int num_merges) {
counters.assert_remove("z");
uint64_t sum = 0;
for (int i = 1; i <= num_merges; ++i) {
resetNumMergeOperatorCalls();
counters.assert_add("z", i);
sum += i;
if (i % (max_num_merges + 1) == 0) {
assert(numMergeOperatorCalls == max_num_merges + 1);
} else {
assert(numMergeOperatorCalls == 0);
}
resetNumMergeOperatorCalls();
assert(counters.assert_get("z") == sum);
assert(numMergeOperatorCalls == i % (max_num_merges + 1));
}
}
void testSingleBatchSuccessiveMerge(
DB* db,
int max_num_merges,
int num_merges) {
assert(num_merges > max_num_merges);
Slice key("BatchSuccessiveMerge");
uint64_t merge_value = 1;
Slice merge_value_slice((char *)&merge_value, sizeof(merge_value));
// Create the batch
WriteBatch batch;
for (int i = 0; i < num_merges; ++i) {
batch.Merge(key, merge_value_slice);
}
// Apply to memtable and count the number of merges
resetNumMergeOperatorCalls();
{
Status s = db->Write(WriteOptions(), &batch);
assert(s.ok());
}
assert(numMergeOperatorCalls ==
num_merges - (num_merges % (max_num_merges + 1)));
// Get the value
resetNumMergeOperatorCalls();
string get_value_str;
{
Status s = db->Get(ReadOptions(), key, &get_value_str);
assert(s.ok());
}
assert(get_value_str.size() == sizeof(uint64_t));
uint64_t get_value = DecodeFixed64(&get_value_str[0]);
assert(get_value == num_merges * merge_value);
assert(numMergeOperatorCalls == (num_merges % (max_num_merges + 1)));
}
void runTest(int argc, const string& dbname, const bool use_ttl = false) {
auto db = OpenDb(dbname, use_ttl);
@ -265,6 +366,19 @@ void runTest(int argc, const string& dbname, const bool use_ttl = false) {
}
DestroyDB(dbname, Options());
db.reset();
{
cout << "Test merge in memtable... \n";
unsigned maxMerge = 5;
auto db = OpenDb(dbname, use_ttl, maxMerge);
MergeBasedCounters counters(db, 0);
testCounters(counters, db.get(), compact);
testSuccessiveMerge(counters, maxMerge, maxMerge * 2);
testSingleBatchSuccessiveMerge(db.get(), 5, 7);
DestroyDB(dbname, Options());
}
}
int main(int argc, char *argv[]) {

58
db/write_batch.cc
View File

@ -21,6 +21,7 @@
#include "rocksdb/write_batch.h"
#include "rocksdb/options.h"
#include "rocksdb/merge_operator.h"
#include "db/dbformat.h"
#include "db/db_impl.h"
#include "db/memtable.h"
@ -203,7 +204,62 @@ class MemTableInserter : public WriteBatch::Handler {
sequence_++;
}
virtual void Merge(const Slice& key, const Slice& value) {
mem_->Add(sequence_, kTypeMerge, key, value);
bool perform_merge = false;
if (options_->max_successive_merges > 0 && db_ != nullptr) {
LookupKey lkey(key, sequence_);
// Count the number of successive merges at the head
// of the key in the memtable
size_t num_merges = mem_->CountSuccessiveMergeEntries(lkey);
if (num_merges >= options_->max_successive_merges) {
perform_merge = true;
}
}
if (perform_merge) {
// 1) Get the existing value
std::string get_value;
// Pass in the sequence number so that we also include previous merge
// operations in the same batch.
SnapshotImpl read_from_snapshot;
read_from_snapshot.number_ = sequence_;
ReadOptions read_options;
read_options.snapshot = &read_from_snapshot;
db_->Get(read_options, key, &get_value);
Slice get_value_slice = Slice(get_value);
// 2) Apply this merge
auto merge_operator = options_->merge_operator.get();
assert(merge_operator);
std::deque<std::string> operands;
operands.push_front(value.ToString());
std::string new_value;
if (!merge_operator->FullMerge(key,
&get_value_slice,
operands,
&new_value,
options_->info_log.get())) {
// Failed to merge!
RecordTick(options_->statistics.get(), NUMBER_MERGE_FAILURES);
// Store the delta in memtable
perform_merge = false;
} else {
// 3) Add value to memtable
mem_->Add(sequence_, kTypeValue, key, new_value);
}
}
if (!perform_merge) {
// Add merge operator to memtable
mem_->Add(sequence_, kTypeMerge, key, value);
}
sequence_++;
}
virtual void Delete(const Slice& key) {

11
include/rocksdb/options.h
View File

@ -643,6 +643,17 @@ struct Options {
// Number of locks used for inplace update
// Default: 10000, if inplace_update_support = true, else 0.
size_t inplace_update_num_locks;
// Maximum number of successive merge operations on a key in the memtable.
//
// When a merge operation is added to the memtable and the maximum number of
// successive merges is reached, the value of the key will be calculated and
// inserted into the memtable instead of the merge operation. This will
// ensure that there are never more than max_successive_merges merge
// operations in the memtable.
//
// Default: 0 (disabled)
size_t max_successive_merges;
};
//

5
util/options.cc
View File

@ -101,7 +101,8 @@ Options::Options()
table_factory(
std::shared_ptr<TableFactory>(new BlockBasedTableFactory())),
inplace_update_support(false),
inplace_update_num_locks(10000) {
inplace_update_num_locks(10000),
max_successive_merges(0) {
assert(memtable_factory.get() != nullptr);
}
@ -292,6 +293,8 @@ Options::Dump(Logger* log) const
inplace_update_support);
Log(log, " Options.inplace_update_num_locks: %zd",
inplace_update_num_locks);
Log(log, " Options.max_successive_merges: %zd",
max_successive_merges);
} // Options::Dump
//