From 80e5b0d944b7651046f8b0e795065eca02a01e59 Mon Sep 17 00:00:00 2001 From: "hans@chromium.org" Date: Tue, 7 Jun 2011 14:40:26 +0000 Subject: [PATCH] sync with upstream @21706995 Fixed race condition reported by Dave Smit (dizzyd@dizzyd,com) on the leveldb mailing list. We were not signalling waiters after a trivial move from level-0. The result was that in some cases (hard to reproduce), a write would get stuck forever waiting for the number of level-0 files to drop below its hard limit. The new code is simpler: there is just one condition variable instead of two, and the condition variable is signalled after every piece of background work finishes. Also, all compaction work (including for manual compactions) is done in the background thread, and therefore we can remove the "compacting_" variable. git-svn-id: https://leveldb.googlecode.com/svn/trunk@31 62dab493-f737-651d-591e-8d6aee1b9529 --- db/db_impl.cc | 91 +++++++++++++++++++++++++++++------------------------------ db/db_impl.h | 12 +++++--- 2 files changed, 53 insertions(+), 50 deletions(-) diff --git a/db/db_impl.cc b/db/db_impl.cc index 9b139ce..abcc761 100644 --- a/db/db_impl.cc +++ b/db/db_impl.cc @@ -119,13 +119,12 @@ DBImpl::DBImpl(const Options& options, const std::string& dbname) db_lock_(NULL), shutting_down_(NULL), bg_cv_(&mutex_), - compacting_cv_(&mutex_), mem_(new MemTable(internal_comparator_)), imm_(NULL), logfile_(NULL), log_(NULL), bg_compaction_scheduled_(false), - compacting_(false) { + manual_compaction_(NULL) { mem_->Ref(); has_imm_.Release_Store(NULL); @@ -141,10 +140,8 @@ DBImpl::~DBImpl() { // Wait for background work to finish mutex_.Lock(); shutting_down_.Release_Store(this); // Any non-NULL value is ok - if (bg_compaction_scheduled_) { - while (bg_compaction_scheduled_) { - bg_cv_.Wait(); - } + while (bg_compaction_scheduled_) { + bg_cv_.Wait(); } mutex_.Unlock(); @@ -437,7 +434,6 @@ Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit) { Status DBImpl::CompactMemTable() { mutex_.AssertHeld(); assert(imm_ != NULL); - assert(compacting_); // Save the contents of the memtable as a new Table VersionEdit edit; @@ -457,7 +453,6 @@ Status DBImpl::CompactMemTable() { DeleteObsoleteFiles(); } - compacting_cv_.SignalAll(); // Wake up waiter even if there was an error return s; } @@ -466,22 +461,18 @@ void DBImpl::TEST_CompactRange( const std::string& begin, const std::string& end) { MutexLock l(&mutex_); - while (compacting_) { - compacting_cv_.Wait(); + while (manual_compaction_ != NULL) { + bg_cv_.Wait(); } - Compaction* c = versions_->CompactRange( - level, - InternalKey(begin, kMaxSequenceNumber, kValueTypeForSeek), - InternalKey(end, 0, static_cast(0))); - - if (c != NULL) { - CompactionState* compact = new CompactionState(c); - DoCompactionWork(compact); // Ignore error in test compaction - CleanupCompaction(compact); - } - - // Start any background compaction that may have been delayed by this thread + ManualCompaction manual; + manual.level = level; + manual.begin = begin; + manual.end = end; + manual_compaction_ = &manual; MaybeScheduleCompaction(); + while (manual_compaction_ == &manual) { + bg_cv_.Wait(); + } } Status DBImpl::TEST_CompactMemTable() { @@ -490,7 +481,7 @@ Status DBImpl::TEST_CompactMemTable() { if (s.ok()) { // Wait until the compaction completes while (imm_ != NULL && bg_error_.ok()) { - compacting_cv_.Wait(); + bg_cv_.Wait(); } if (imm_ != NULL) { s = bg_error_; @@ -503,11 +494,11 @@ void DBImpl::MaybeScheduleCompaction() { mutex_.AssertHeld(); if (bg_compaction_scheduled_) { // Already scheduled - } else if (compacting_) { - // Some other thread is running a compaction. Do not conflict with it. } else if (shutting_down_.Acquire_Load()) { // DB is being deleted; no more background compactions - } else if (imm_ == NULL && !versions_->NeedsCompaction()) { + } else if (imm_ == NULL && + manual_compaction_ == NULL && + !versions_->NeedsCompaction()) { // No work to be done } else { bg_compaction_scheduled_ = true; @@ -522,38 +513,41 @@ void DBImpl::BGWork(void* db) { void DBImpl::BackgroundCall() { MutexLock l(&mutex_); assert(bg_compaction_scheduled_); - if (!shutting_down_.Acquire_Load() && - !compacting_) { + if (!shutting_down_.Acquire_Load()) { BackgroundCompaction(); } bg_compaction_scheduled_ = false; - bg_cv_.SignalAll(); // Previous compaction may have produced too many files in a level, // so reschedule another compaction if needed. MaybeScheduleCompaction(); + bg_cv_.SignalAll(); } void DBImpl::BackgroundCompaction() { mutex_.AssertHeld(); - assert(!compacting_); if (imm_ != NULL) { - compacting_ = true; CompactMemTable(); - compacting_ = false; - compacting_cv_.SignalAll(); return; } - Compaction* c = versions_->PickCompaction(); - if (c == NULL) { - // Nothing to do - return; + Compaction* c; + bool is_manual = (manual_compaction_ != NULL); + if (is_manual) { + const ManualCompaction* m = manual_compaction_; + c = versions_->CompactRange( + m->level, + InternalKey(m->begin, kMaxSequenceNumber, kValueTypeForSeek), + InternalKey(m->end, 0, static_cast(0))); + } else { + c = versions_->PickCompaction(); } Status status; - if (c->IsTrivialMove()) { + if (c == NULL) { + // Nothing to do + } else if (!is_manual && c->IsTrivialMove()) { // Move file to next level assert(c->num_input_files(0) == 1); FileMetaData* f = c->input(0, 0); @@ -561,11 +555,13 @@ void DBImpl::BackgroundCompaction() { c->edit()->AddFile(c->level() + 1, f->number, f->file_size, f->smallest, f->largest); status = versions_->LogAndApply(c->edit()); - Log(env_, options_.info_log, "Moved #%lld to level-%d %lld bytes %s\n", + VersionSet::LevelSummaryStorage tmp; + Log(env_, options_.info_log, "Moved #%lld to level-%d %lld bytes %s: %s\n", static_cast(f->number), c->level() + 1, static_cast(f->file_size), - status.ToString().c_str()); + status.ToString().c_str(), + versions_->LevelSummary(&tmp)); } else { CompactionState* compact = new CompactionState(c); status = DoCompactionWork(compact); @@ -584,6 +580,11 @@ void DBImpl::BackgroundCompaction() { bg_error_ = status; } } + + if (is_manual) { + // Mark it as done + manual_compaction_ = NULL; + } } void DBImpl::CleanupCompaction(CompactionState* compact) { @@ -734,7 +735,6 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) { } // Release mutex while we're actually doing the compaction work - compacting_ = true; mutex_.Unlock(); Iterator* input = versions_->MakeInputIterator(compact->compaction); @@ -751,7 +751,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) { mutex_.Lock(); if (imm_ != NULL) { CompactMemTable(); - compacting_cv_.SignalAll(); // Wakeup MakeRoomForWrite() if necessary + bg_cv_.SignalAll(); // Wakeup MakeRoomForWrite() if necessary } mutex_.Unlock(); imm_micros += (env_->NowMicros() - imm_start); @@ -867,8 +867,6 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) { if (status.ok()) { status = InstallCompactionResults(compact); } - compacting_ = false; - compacting_cv_.SignalAll(); VersionSet::LevelSummaryStorage tmp; Log(env_, options_.info_log, "compacted to: %s", versions_->LevelSummary(&tmp)); @@ -1038,10 +1036,11 @@ Status DBImpl::MakeRoomForWrite(bool force) { } else if (imm_ != NULL) { // We have filled up the current memtable, but the previous // one is still being compacted, so we wait. - compacting_cv_.Wait(); + bg_cv_.Wait(); } else if (versions_->NumLevelFiles(0) >= config::kL0_StopWritesTrigger) { // There are too many level-0 files. - compacting_cv_.Wait(); + Log(env_, options_.info_log, "waiting...\n"); + bg_cv_.Wait(); } else { // Attempt to switch to a new memtable and trigger compaction of old assert(versions_->PrevLogNumber() == 0); diff --git a/db/db_impl.h b/db/db_impl.h index c23ae00..84ce154 100644 --- a/db/db_impl.h +++ b/db/db_impl.h @@ -119,8 +119,7 @@ class DBImpl : public DB { // State below is protected by mutex_ port::Mutex mutex_; port::AtomicPointer shutting_down_; - port::CondVar bg_cv_; // Signalled when !bg_compaction_scheduled_ - port::CondVar compacting_cv_; // Signalled when !compacting_ + port::CondVar bg_cv_; // Signalled when background work finishes MemTable* mem_; MemTable* imm_; // Memtable being compacted port::AtomicPointer has_imm_; // So bg thread can detect non-NULL imm_ @@ -135,8 +134,13 @@ class DBImpl : public DB { // Has a background compaction been scheduled or is running? bool bg_compaction_scheduled_; - // Is there a compaction running? - bool compacting_; + // Information for a manual compaction + struct ManualCompaction { + int level; + std::string begin; + std::string end; + }; + ManualCompaction* manual_compaction_; VersionSet* versions_;