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cache SuperVersion in thread local storage to avoid mutex lock 

Summary: as title

Test Plan:
asan_check
will post results later

Reviewers: haobo, igor, dhruba, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16257
This commit is contained in:
Lei Jin 2014-02-27 11:38:55 -08:00
parent e41c060a06
commit ad0c3747cb
8 changed files with 176 additions and 48 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

138
db/db_impl.cc
View File

@ -38,6 +38,7 @@
#include "db/version_set.h"
#include "db/write_batch_internal.h"
#include "port/port.h"
#include "port/likely.h"
#include "rocksdb/compaction_filter.h"
#include "rocksdb/db.h"
#include "rocksdb/env.h"
@ -270,6 +271,7 @@ DBImpl::DBImpl(const Options& options, const std::string& dbname)
logfile_number_(0),
super_version_(nullptr),
super_version_number_(0),
local_sv_(new ThreadLocalPtr(&SuperVersionUnrefHandle)),
tmp_batch_(),
bg_compaction_scheduled_(0),
bg_manual_only_(0),
@ -288,7 +290,8 @@ DBImpl::DBImpl(const Options& options, const std::string& dbname)
delayed_writes_(0),
storage_options_(options),
bg_work_gate_closed_(false),
refitting_level_(false) {
refitting_level_(false),
opened_successfully_(false) {
mem_->Ref();
env_->GetAbsolutePath(dbname, &db_absolute_path_);
@ -319,12 +322,11 @@ DBImpl::DBImpl(const Options& options, const std::string& dbname)
}
DBImpl::~DBImpl() {
autovector<MemTable*> to_delete;
// Wait for background work to finish
if (flush_on_destroy_ && mem_->GetFirstSequenceNumber() != 0) {
FlushMemTable(FlushOptions());
}
mutex_.Lock();
shutting_down_.Release_Store(this); // Any non-nullptr value is ok
while (bg_compaction_scheduled_ ||
@ -332,6 +334,34 @@ DBImpl::~DBImpl() {
bg_logstats_scheduled_) {
bg_cv_.Wait();
}
mutex_.Unlock();
// Release SuperVersion reference kept in ThreadLocalPtr.
// This must be done outside of mutex_ since unref handler can lock mutex.
// It also needs to be done after FlushMemTable, which can trigger local_sv_
// access.
delete local_sv_;
mutex_.Lock();
if (options_.allow_thread_local) {
// Clean up obsolete files due to SuperVersion release.
// (1) Need to delete to obsolete files before closing because RepairDB()
// scans all existing files in the file system and builds manifest file.
// Keeping obsolete files confuses the repair process.
// (2) Need to check if we Open()/Recover() the DB successfully before
// deleting because if VersionSet recover fails (may be due to corrupted
// manifest file), it is not able to identify live files correctly. As a
// result, all "live" files can get deleted by accident. However, corrupted
// manifest is recoverable by RepairDB().
if (opened_successfully_) {
DeletionState deletion_state;
FindObsoleteFiles(deletion_state, true);
// manifest number starting from 2
deletion_state.manifest_file_number = 1;
PurgeObsoleteFiles(deletion_state);
}
}
if (super_version_ != nullptr) {
bool is_last_reference __attribute__((unused));
is_last_reference = super_version_->Unref();
@ -349,6 +379,7 @@ DBImpl::~DBImpl() {
delete mem_->Unref();
}
autovector<MemTable*> to_delete;
imm_.current()->Unref(&to_delete);
for (MemTable* m: to_delete) {
delete m;
@ -1286,6 +1317,10 @@ Status DBImpl::FlushMemTableToOutputFile(bool* madeProgress,
if (s.ok()) {
InstallSuperVersion(deletion_state);
// Reset SuperVersions cached in thread local storage
if (options_.allow_thread_local) {
ResetThreadLocalSuperVersions(&deletion_state);
}
if (madeProgress) {
*madeProgress = 1;
}
@ -2811,26 +2846,21 @@ Status DBImpl::Get(const ReadOptions& options,
// DeletionState gets created and destructed outside of the lock -- we
// use this convinently to:
// * malloc one SuperVersion() outside of the lock -- new_superversion
// * delete one SuperVersion() outside of the lock -- superversion_to_free
// * delete SuperVersion()s outside of the lock -- superversions_to_free
//
// However, if InstallSuperVersion() gets called twice with the same,
// deletion_state, we can't reuse the SuperVersion() that got malloced because
// first call already used it. In that rare case, we take a hit and create a
// new SuperVersion() inside of the mutex. We do similar thing
// for superversion_to_free
// new SuperVersion() inside of the mutex.
void DBImpl::InstallSuperVersion(DeletionState& deletion_state) {
mutex_.AssertHeld();
// if new_superversion == nullptr, it means somebody already used it
SuperVersion* new_superversion =
(deletion_state.new_superversion != nullptr) ?
deletion_state.new_superversion : new SuperVersion();
SuperVersion* old_superversion = InstallSuperVersion(new_superversion);
deletion_state.new_superversion = nullptr;
if (deletion_state.superversion_to_free != nullptr) {
// somebody already put it there
delete old_superversion;
} else {
deletion_state.superversion_to_free = old_superversion;
}
deletion_state.superversions_to_free.push_back(old_superversion);
}
DBImpl::SuperVersion* DBImpl::InstallSuperVersion(
@ -2839,7 +2869,10 @@ DBImpl::SuperVersion* DBImpl::InstallSuperVersion(
new_superversion->Init(mem_, imm_.current(), versions_->current());
SuperVersion* old_superversion = super_version_;
super_version_ = new_superversion;
super_version_->db = this;
++super_version_number_;
super_version_->version_number = super_version_number_;
if (old_superversion != nullptr && old_superversion->Unref()) {
old_superversion->Cleanup();
return old_superversion; // will let caller delete outside of mutex
@ -2847,6 +2880,20 @@ DBImpl::SuperVersion* DBImpl::InstallSuperVersion(
return nullptr;
}
void DBImpl::ResetThreadLocalSuperVersions(DeletionState* deletion_state) {
mutex_.AssertHeld();
autovector<void*> sv_ptrs;
local_sv_->Scrape(&sv_ptrs);
for (auto ptr : sv_ptrs) {
assert(ptr);
auto sv = static_cast<SuperVersion*>(ptr);
if (static_cast<SuperVersion*>(ptr)->Unref()) {
sv->Cleanup();
deletion_state->superversions_to_free.push_back(sv);
}
}
}
Status DBImpl::GetImpl(const ReadOptions& options,
const Slice& key,
std::string* value,
@ -2864,11 +2911,42 @@ Status DBImpl::GetImpl(const ReadOptions& options,
snapshot = versions_->LastSequence();
}
// This can be replaced by using atomics and spinlock instead of big mutex
// Acquire SuperVersion
SuperVersion* sv = nullptr;
if (LIKELY(options_.allow_thread_local)) {
// The SuperVersion is cached in thread local storage to avoid acquiring
// mutex when SuperVersion does not change since the last use. When a new
// SuperVersion is installed, the compaction or flush thread cleans up
// cached SuperVersion in all existing thread local storage. To avoid
// acquiring mutex for this operation, we use atomic Swap() on the thread
// local pointer to guarantee exclusive access. If the thread local pointer
// is being used while a new SuperVersion is installed, the cached
// SuperVersion can become stale. It will eventually get refreshed either
// on the next GetImpl() call or next SuperVersion installation.
sv = static_cast<SuperVersion*>(local_sv_->Swap(nullptr));
if (!sv || sv->version_number !=
super_version_number_.load(std::memory_order_relaxed)) {
RecordTick(options_.statistics.get(), NUMBER_SUPERVERSION_UPDATES);
SuperVersion* sv_to_delete = nullptr;
if (sv && sv->Unref()) {
mutex_.Lock();
SuperVersion* get_version = super_version_->Ref();
sv->Cleanup();
sv_to_delete = sv;
} else {
mutex_.Lock();
}
sv = super_version_->Ref();
mutex_.Unlock();
delete sv_to_delete;
}
} else {
mutex_.Lock();
sv = super_version_->Ref();
mutex_.Unlock();
}
bool have_stat_update = false;
Version::GetStats stats;
@ -2880,17 +2958,17 @@ Status DBImpl::GetImpl(const ReadOptions& options,
// merge_operands will contain the sequence of merges in the latter case.
LookupKey lkey(key, snapshot);
BumpPerfTime(&perf_context.get_snapshot_time, &snapshot_timer);
if (get_version->mem->Get(lkey, value, &s, merge_context, options_)) {
if (sv->mem->Get(lkey, value, &s, merge_context, options_)) {
// Done
RecordTick(options_.statistics.get(), MEMTABLE_HIT);
} else if (get_version->imm->Get(lkey, value, &s, merge_context, options_)) {
} else if (sv->imm->Get(lkey, value, &s, merge_context, options_)) {
// Done
RecordTick(options_.statistics.get(), MEMTABLE_HIT);
} else {
StopWatchNano from_files_timer(env_, false);
StartPerfTimer(&from_files_timer);
get_version->current->Get(options, lkey, value, &s, &merge_context, &stats,
sv->current->Get(options, lkey, value, &s, &merge_context, &stats,
options_, value_found);
have_stat_update = true;
BumpPerfTime(&perf_context.get_from_output_files_time, &from_files_timer);
@ -2900,31 +2978,32 @@ Status DBImpl::GetImpl(const ReadOptions& options,
StopWatchNano post_process_timer(env_, false);
StartPerfTimer(&post_process_timer);
bool delete_get_version = false;
if (!options_.disable_seek_compaction && have_stat_update) {
mutex_.Lock();
if (get_version->current->UpdateStats(stats)) {
if (sv->current->UpdateStats(stats)) {
MaybeScheduleFlushOrCompaction();
}
if (get_version->Unref()) {
get_version->Cleanup();
delete_get_version = true;
}
mutex_.Unlock();
}
// Release SuperVersion
if (LIKELY(options_.allow_thread_local)) {
// Put the SuperVersion back
local_sv_->Reset(static_cast<void*>(sv));
} else {
if (get_version->Unref()) {
bool delete_sv = false;
if (sv->Unref()) {
mutex_.Lock();
get_version->Cleanup();
sv->Cleanup();
mutex_.Unlock();
delete_get_version = true;
delete_sv = true;
}
if (delete_sv) {
delete sv;
}
if (delete_get_version) {
delete get_version;
}
// Note, tickers are atomic now - no lock protection needed any more.
RecordTick(options_.statistics.get(), NUMBER_KEYS_READ);
RecordTick(options_.statistics.get(), BYTES_READ, value->size());
BumpPerfTime(&perf_context.get_post_process_time, &post_process_timer);
@ -3772,6 +3851,7 @@ Status DB::Open(const Options& options, const std::string& dbname, DB** dbptr) {
impl->mutex_.Unlock();
if (s.ok()) {
impl->opened_successfully_ = true;
*dbptr = impl;
} else {
delete impl;

31
db/db_impl.h
View File

@ -26,6 +26,7 @@
#include "rocksdb/transaction_log.h"
#include "util/autovector.h"
#include "util/stats_logger.h"
#include "util/thread_local.h"
#include "db/internal_stats.h"
namespace rocksdb {
@ -152,6 +153,9 @@ class DBImpl : public DB {
// all memtables that we need to free through this vector. We then
// delete all those memtables outside of mutex, during destruction
autovector<MemTable*> to_delete;
// Version number of the current SuperVersion
uint64_t version_number;
DBImpl* db;
// should be called outside the mutex
SuperVersion() = default;
@ -170,6 +174,16 @@ class DBImpl : public DB {
Version* new_current);
};
static void SuperVersionUnrefHandle(void* ptr) {
DBImpl::SuperVersion* sv = static_cast<DBImpl::SuperVersion*>(ptr);
if (sv->Unref()) {
sv->db->mutex_.Lock();
sv->Cleanup();
sv->db->mutex_.Unlock();
delete sv;
}
}
// needed for CleanupIteratorState
struct DeletionState {
inline bool HaveSomethingToDelete() const {
@ -195,7 +209,7 @@ class DBImpl : public DB {
// a list of memtables to be free
autovector<MemTable*> memtables_to_free;
SuperVersion* superversion_to_free; // if nullptr nothing to free
autovector<SuperVersion*> superversions_to_free;
SuperVersion* new_superversion; // if nullptr no new superversion
@ -207,7 +221,6 @@ class DBImpl : public DB {
manifest_file_number = 0;
log_number = 0;
prev_log_number = 0;
superversion_to_free = nullptr;
new_superversion =
create_superversion ? new SuperVersion() : nullptr;
}
@ -217,8 +230,10 @@ class DBImpl : public DB {
for (auto m : memtables_to_free) {
delete m;
}
// free superversion. if nullptr, this will be noop
delete superversion_to_free;
// free superversions
for (auto s : superversions_to_free) {
delete s;
}
// if new_superversion was not used, it will be non-nullptr and needs
// to be freed here
delete new_superversion;
@ -400,6 +415,9 @@ class DBImpl : public DB {
// InstallSuperVersion(), i.e. incremented every time super_version_
// changes.
std::atomic<uint64_t> super_version_number_;
// Thread's local copy of SuperVersion pointer
// This needs to be destructed after mutex_
ThreadLocalPtr* local_sv_;
std::string host_name_;
@ -489,6 +507,9 @@ class DBImpl : public DB {
// Guard against multiple concurrent refitting
bool refitting_level_;
// Indicate DB was opened successfully
bool opened_successfully_;
// No copying allowed
DBImpl(const DBImpl&);
void operator=(const DBImpl&);
@ -515,6 +536,8 @@ class DBImpl : public DB {
// deletion_state which can have new_superversion already allocated.
void InstallSuperVersion(DeletionState& deletion_state);
void ResetThreadLocalSuperVersions(DeletionState* deletion_state);
virtual Status GetPropertiesOfAllTables(TablePropertiesCollection* props)
override;

4
include/rocksdb/options.h
View File

@ -714,6 +714,10 @@ struct Options {
//
// Default: 0 (disabled)
size_t max_successive_merges;
// Allow RocksDB to use thread local storage to optimize performance.
// Default: true
bool allow_thread_local;
};
//

5
include/rocksdb/statistics.h
View File

@ -122,6 +122,7 @@ enum Tickers {
// Number of table's properties loaded directly from file, without creating
// table reader object.
NUMBER_DIRECT_LOAD_TABLE_PROPERTIES,
NUMBER_SUPERVERSION_UPDATES,
TICKER_ENUM_MAX
};
@ -176,7 +177,9 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
{COMPACT_READ_BYTES, "rocksdb.compact.read.bytes"},
{COMPACT_WRITE_BYTES, "rocksdb.compact.write.bytes"},
{NUMBER_DIRECT_LOAD_TABLE_PROPERTIES,
"rocksdb.number.direct.load.table.properties"}, };
"rocksdb.number.direct.load.table.properties"},
{NUMBER_SUPERVERSION_UPDATES, "rocksdb.number.superversion_updates"},
};
/**
* Keep adding histogram's here.

21
port/likely.h Normal file
View File

@ -0,0 +1,21 @@
// Copyright (c) 2013, Facebook, Inc. All rights reserved.
// This source code is licensed under the BSD-style license found in the
// LICENSE file in the root directory of this source tree. An additional grant
// of patent rights can be found in the PATENTS file in the same directory.
//
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#ifndef PORT_LIKELY_H_
#define PORT_LIKELY_H_
#if defined(__GNUC__) && __GNUC__ >= 4
#define LIKELY(x) (__builtin_expect((x), 1))
#define UNLIKELY(x) (__builtin_expect((x), 0))
#else
#define LIKELY(x) (x)
#define UNLIKELY(x) (x)
#endif
#endif // PORT_LIKELY_H_

3
util/options.cc
View File

@ -110,7 +110,8 @@ Options::Options()
inplace_callback(nullptr),
memtable_prefix_bloom_bits(0),
memtable_prefix_bloom_probes(6),
max_successive_merges(0) {
max_successive_merges(0),
allow_thread_local(true) {
assert(memtable_factory.get() != nullptr);
}

2
util/statistics.h
View File

@ -7,11 +7,11 @@
#include "rocksdb/statistics.h"
#include "util/histogram.h"
#include "util/mutexlock.h"
#include "port/likely.h"
#include <vector>
#include <atomic>
#define UNLIKELY(val) (__builtin_expect((val), 0))
namespace rocksdb {

6
util/thread_local.cc
View File

@ -9,12 +9,8 @@
#include "util/thread_local.h"
#include "util/mutexlock.h"
#include "port/likely.h"
#if defined(__GNUC__) && __GNUC__ >= 4
#define UNLIKELY(x) (__builtin_expect((x), 0))
#else
#define UNLIKELY(x) (x)
#endif
namespace rocksdb {