Do not hold mutex when write keys if not necessary (facebook#7516)

Summary:
RocksDB will acquire the global mutex of db instance for every time when user calls `Write`.  When RocksDB schedules a lot of compaction jobs,   it will compete the mutex with write thread and it will hurt the write performance.

I want to use log_write_mutex to replace the global mutex in most case so that we do not acquire it in write-thread unless there is a write-stall event or a write-buffer-full event occur.

Pull Request resolved: facebook#7516

Test Plan:
1. make check
2. CI
3. COMPILE_WITH_TSAN=1 make db_stress
make crash_test
make crash_test_with_multiops_wp_txn
make crash_test_with_multiops_wc_txn
make crash_test_with_atomic_flush

Reviewed By: siying

Differential Revision: D36908702

Pulled By: riversand963

fbshipit-source-id: 59b13881f4f5c0a58fd3ca79128a396d9cd98efe
Signed-off-by: tabokie <[email protected]>

Author: Little-Wallace

HISTORY.md

@@ -21,6 +21,7 @@
 
 ## Behavior Changes
 * For track_and_verify_wals_in_manifest, revert to the original behavior before #10087: syncing of live WAL file is not tracked, and we track only the synced sizes of **closed** WALs. (PR #10330).
+* DB::Write does not hold global `mutex_` if this db instance does not need to switch wal and mem-table (#7516).
 
 ## 6.29.5 (03/29/2022)
 ### Bug Fixes

db/db_compaction_test.cc

@@ -5333,18 +5333,10 @@ TEST_P(DBCompactionTestWithParam, FixFileIngestionCompactionDeadlock) {
     for (int j = 0; j != kNumKeysPerFile; ++j) {
       ASSERT_OK(Put(Key(j), rnd.RandomString(990)));
     }
-    if (0 == i) {
-      // When we reach here, the memtables have kNumKeysPerFile keys. Note that
-      // flush is not yet triggered. We need to write an extra key so that the
-      // write path will call PreprocessWrite and flush the previous key-value
-      // pairs to e flushed. After that, there will be the newest key in the
-      // memtable, and a bunch of L0 files. Since there is already one key in
-      // the memtable, then for i = 1, 2, ..., we do not have to write this
-      // extra key to trigger flush.
-      ASSERT_OK(Put("", ""));
+    if (i > 0) {
+      ASSERT_OK(dbfull()->TEST_WaitForFlushMemTable());
+      ASSERT_EQ(NumTableFilesAtLevel(0 /*level*/, 0 /*cf*/), i);
     }
-    ASSERT_OK(dbfull()->TEST_WaitForFlushMemTable());
-    ASSERT_EQ(NumTableFilesAtLevel(0 /*level*/, 0 /*cf*/), i + 1);
   }
   // When we reach this point, there will be level0_stop_writes_trigger L0
   // files and one extra key (99) in memory, which overlaps with the external

db/db_impl/db_impl.cc

@@ -181,7 +181,7 @@ DBImpl::DBImpl(const DBOptions& options, const std::string& dbname,
       log_dir_synced_(false),
       log_empty_(true),
       persist_stats_cf_handle_(nullptr),
-      log_sync_cv_(&mutex_),
+      log_sync_cv_(&log_write_mutex_),
       total_log_size_(0),
       is_snapshot_supported_(true),
       write_buffer_manager_(immutable_db_options_.write_buffer_manager.get()),
@@ -271,6 +271,8 @@ DBImpl::DBImpl(const DBOptions& options, const std::string& dbname,
   mutable_db_options_.Dump(immutable_db_options_.info_log.get());
   DumpSupportInfo(immutable_db_options_.info_log.get());
 
+  max_total_wal_size_.store(mutable_db_options_.max_total_wal_size,
+                            std::memory_order_relaxed);
   if (write_buffer_manager_) {
     wbm_stall_.reset(new WBMStallInterface());
   }
@@ -641,26 +643,28 @@ Status DBImpl::CloseHelper() {
     job_context.Clean();
     mutex_.Lock();
   }
-
-  for (auto l : logs_to_free_) {
-    delete l;
-  }
-  for (auto& log : logs_) {
-    uint64_t log_number = log.writer->get_log_number();
-    Status s = log.ClearWriter();
-    if (!s.ok()) {
-      ROCKS_LOG_WARN(
-          immutable_db_options_.info_log,
-          "Unable to Sync WAL file %s with error -- %s",
-          LogFileName(immutable_db_options_.GetWalDir(), log_number).c_str(),
-          s.ToString().c_str());
-      // Retain the first error
-      if (ret.ok()) {
-        ret = s;
+  {
+    InstrumentedMutexLock lock(&log_write_mutex_);
+    for (auto l : logs_to_free_) {
+      delete l;
+    }
+    for (auto& log : logs_) {
+      uint64_t log_number = log.writer->get_log_number();
+      Status s = log.ClearWriter();
+      if (!s.ok()) {
+        ROCKS_LOG_WARN(
+            immutable_db_options_.info_log,
+            "Unable to Sync WAL file %s with error -- %s",
+            LogFileName(immutable_db_options_.GetWalDir(), log_number).c_str(),
+            s.ToString().c_str());
+        // Retain the first error
+        if (ret.ok()) {
+          ret = s;
+        }
       }
     }
+    logs_.clear();
   }
-  logs_.clear();
 
   // Table cache may have table handles holding blocks from the block cache.
   // We need to release them before the block cache is destroyed. The block
@@ -1046,6 +1050,7 @@ Status DBImpl::TablesRangeTombstoneSummary(ColumnFamilyHandle* column_family,
 }
 
 void DBImpl::ScheduleBgLogWriterClose(JobContext* job_context) {
+  mutex_.AssertHeld();
   if (!job_context->logs_to_free.empty()) {
     for (auto l : job_context->logs_to_free) {
       AddToLogsToFreeQueue(l);
@@ -1225,6 +1230,11 @@ Status DBImpl::SetDBOptions(
             new_options.stats_persist_period_sec);
         mutex_.Lock();
       }
+      if (new_options.max_total_wal_size !=
+          mutable_db_options_.max_total_wal_size) {
+        max_total_wal_size_.store(new_options.max_total_wal_size,
+                                  std::memory_order_release);
+      }
       write_controller_.set_max_delayed_write_rate(
           new_options.delayed_write_rate);
       table_cache_.get()->SetCapacity(new_options.max_open_files == -1
@@ -1345,7 +1355,7 @@ Status DBImpl::SyncWAL() {
   uint64_t current_log_number;
 
   {
-    InstrumentedMutexLock l(&mutex_);
+    InstrumentedMutexLock l(&log_write_mutex_);
     assert(!logs_.empty());
 
     // This SyncWAL() call only cares about logs up to this number.
@@ -1402,19 +1412,37 @@ Status DBImpl::SyncWAL() {
   TEST_SYNC_POINT("DBWALTest::SyncWALNotWaitWrite:2");
 
   TEST_SYNC_POINT("DBImpl::SyncWAL:BeforeMarkLogsSynced:1");
+  VersionEdit synced_wals;
   {
-    InstrumentedMutexLock l(&mutex_);
+    InstrumentedMutexLock l(&log_write_mutex_);
     if (status.ok()) {
-      status = MarkLogsSynced(current_log_number, need_log_dir_sync);
+      MarkLogsSynced(current_log_number, need_log_dir_sync, &synced_wals);
     } else {
       MarkLogsNotSynced(current_log_number);
     }
   }
+  if (status.ok() && synced_wals.IsWalAddition()) {
+    InstrumentedMutexLock l(&mutex_);
+    status = ApplyWALToManifest(&synced_wals);
+  }
+
   TEST_SYNC_POINT("DBImpl::SyncWAL:BeforeMarkLogsSynced:2");
 
   return status;
 }
 
+Status DBImpl::ApplyWALToManifest(VersionEdit* synced_wals) {
+  // not empty, write to MANIFEST.
+  mutex_.AssertHeld();
+  Status status =
+      versions_->LogAndApplyToDefaultColumnFamily(synced_wals, &mutex_);
+  if (!status.ok() && versions_->io_status().IsIOError()) {
+    status = error_handler_.SetBGError(versions_->io_status(),
+                                       BackgroundErrorReason::kManifestWrite);
+  }
+  return status;
+}
+
 Status DBImpl::LockWAL() {
   log_write_mutex_.Lock();
   auto cur_log_writer = logs_.back().writer;
@@ -1434,24 +1462,22 @@ Status DBImpl::UnlockWAL() {
   return Status::OK();
 }
 
-Status DBImpl::MarkLogsSynced(uint64_t up_to, bool synced_dir) {
-  mutex_.AssertHeld();
+void DBImpl::MarkLogsSynced(uint64_t up_to, bool synced_dir,
+                            VersionEdit* synced_wals) {
+  log_write_mutex_.AssertHeld();
   if (synced_dir && logfile_number_ == up_to) {
     log_dir_synced_ = true;
   }
-  VersionEdit synced_wals;
   for (auto it = logs_.begin(); it != logs_.end() && it->number <= up_to;) {
     auto& wal = *it;
     assert(wal.IsSyncing());
 
     if (logs_.size() > 1) {
       if (immutable_db_options_.track_and_verify_wals_in_manifest &&
           wal.GetPreSyncSize() > 0) {
-        synced_wals.AddWal(wal.number, WalMetadata(wal.GetPreSyncSize()));
+        synced_wals->AddWal(wal.number, WalMetadata(wal.GetPreSyncSize()));
       }
       logs_to_free_.push_back(wal.ReleaseWriter());
-      // To modify logs_ both mutex_ and log_write_mutex_ must be held
-      InstrumentedMutexLock l(&log_write_mutex_);
       it = logs_.erase(it);
     } else {
       wal.FinishSync();
@@ -1460,22 +1486,11 @@ Status DBImpl::MarkLogsSynced(uint64_t up_to, bool synced_dir) {
   }
   assert(logs_.empty() || logs_[0].number > up_to ||
          (logs_.size() == 1 && !logs_[0].IsSyncing()));
-
-  Status s;
-  if (synced_wals.IsWalAddition()) {
-    // not empty, write to MANIFEST.
-    s = versions_->LogAndApplyToDefaultColumnFamily(&synced_wals, &mutex_);
-    if (!s.ok() && versions_->io_status().IsIOError()) {
-      s = error_handler_.SetBGError(versions_->io_status(),
-                                    BackgroundErrorReason::kManifestWrite);
-    }
-  }
   log_sync_cv_.SignalAll();
-  return s;
 }
 
 void DBImpl::MarkLogsNotSynced(uint64_t up_to) {
-  mutex_.AssertHeld();
+  log_write_mutex_.AssertHeld();
   for (auto it = logs_.begin(); it != logs_.end() && it->number <= up_to;
        ++it) {
     auto& wal = *it;