log flush reason for better debugging experience

Summary:
It's always a mystery from the logs why flush was triggered -- user triggered it manually, WriteBufferManager triggered it,  logs were full, write buffer was full, etc.
This PR logs Flush reason whenever a flush is scheduled.
Closes https://github.com/facebook/rocksdb/pull/3401

Differential Revision: D6788142

Pulled By: miasantreble

fbshipit-source-id: a867e54d493c06adf5172bd36a180fb3faae3511

db/column_family.cc

@@ -381,6 +381,7 @@ ColumnFamilyData::ColumnFamilyData(
       next_(nullptr),
       prev_(nullptr),
       log_number_(0),
+      flush_reason_(FlushReason::kUnknown),
       column_family_set_(column_family_set),
       pending_flush_(false),
       pending_compaction_(false),

db/column_family.h

@@ -202,6 +202,10 @@ class ColumnFamilyData {
   void SetLogNumber(uint64_t log_number) { log_number_ = log_number; }
   uint64_t GetLogNumber() const { return log_number_; }
 
+  void SetFlushReason(FlushReason flush_reason) {
+    flush_reason_ = flush_reason;
+  }
+  FlushReason GetFlushReason() const { return flush_reason_; }
   // thread-safe
   const EnvOptions* soptions() const;
   const ImmutableCFOptions* ioptions() const { return &ioptions_; }
@@ -404,6 +408,8 @@ class ColumnFamilyData {
   // recovered from
   uint64_t log_number_;
 
+  FlushReason flush_reason_;
+
   // An object that keeps all the compaction stats
   // and picks the next compaction
   std::unique_ptr<CompactionPicker> compaction_picker_;

db/db_filesnapshot.cc

@@ -93,7 +93,7 @@ Status DBImpl::GetLiveFiles(std::vector<std::string>& ret,
       }
       cfd->Ref();
       mutex_.Unlock();
-      status = FlushMemTable(cfd, FlushOptions());
+      status = FlushMemTable(cfd, FlushOptions(), FlushReason::kGetLiveFiles);
       TEST_SYNC_POINT("DBImpl::GetLiveFiles:1");
       TEST_SYNC_POINT("DBImpl::GetLiveFiles:2");
       mutex_.Lock();

db/db_impl.cc

@@ -258,7 +258,7 @@ void DBImpl::CancelAllBackgroundWork(bool wait) {
       if (!cfd->IsDropped() && cfd->initialized() && !cfd->mem()->IsEmpty()) {
         cfd->Ref();
         mutex_.Unlock();
-        FlushMemTable(cfd, FlushOptions());
+        FlushMemTable(cfd, FlushOptions(), FlushReason::kShutDown);
         mutex_.Lock();
         cfd->Unref();
       }
@@ -2826,7 +2826,9 @@ Status DBImpl::IngestExternalFile(
                                &need_flush);
       if (status.ok() && need_flush) {
         mutex_.Unlock();
-        status = FlushMemTable(cfd, FlushOptions(), true /* writes_stopped */);
+        status = FlushMemTable(cfd, FlushOptions(),
+                               FlushReason::kExternalFileIngestion,
+                               true /* writes_stopped */);
         mutex_.Lock();
       }
     }

db/db_impl.h

@@ -819,7 +819,7 @@ class DBImpl : public DB {
 
   // Force current memtable contents to be flushed.
   Status FlushMemTable(ColumnFamilyData* cfd, const FlushOptions& options,
-                       bool writes_stopped = false);
+                       FlushReason flush_reason, bool writes_stopped = false);
 
   // Wait for memtable flushed.
   // If flush_memtable_id is non-null, wait until the memtable with the ID
@@ -881,7 +881,7 @@ class DBImpl : public DB {
   ColumnFamilyData* GetColumnFamilyDataByName(const std::string& cf_name);
 
   void MaybeScheduleFlushOrCompaction();
-  void SchedulePendingFlush(ColumnFamilyData* cfd);
+  void SchedulePendingFlush(ColumnFamilyData* cfd, FlushReason flush_reason);
   void SchedulePendingCompaction(ColumnFamilyData* cfd);
   void SchedulePendingPurge(std::string fname, FileType type, uint64_t number,
                             uint32_t path_id, int job_id);
@@ -920,7 +920,7 @@ class DBImpl : public DB {
   // helper functions for adding and removing from flush & compaction queues
   void AddToCompactionQueue(ColumnFamilyData* cfd);
   ColumnFamilyData* PopFirstFromCompactionQueue();
-  void AddToFlushQueue(ColumnFamilyData* cfd);
+  void AddToFlushQueue(ColumnFamilyData* cfd, FlushReason flush_reason);
   ColumnFamilyData* PopFirstFromFlushQueue();
 
   // helper function to call after some of the logs_ were synced

db/db_impl_compaction_flush.cc

@@ -23,6 +23,7 @@
 #include "util/sync_point.h"
 
 namespace rocksdb {
+
 Status DBImpl::SyncClosedLogs(JobContext* job_context) {
   TEST_SYNC_POINT("DBImpl::SyncClosedLogs:Start");
   mutex_.AssertHeld();
@@ -222,6 +223,7 @@ void DBImpl::NotifyOnFlushBegin(ColumnFamilyData* cfd, FileMetaData* file_meta,
     info.smallest_seqno = file_meta->smallest_seqno;
     info.largest_seqno = file_meta->largest_seqno;
     info.table_properties = prop;
+    info.flush_reason = cfd->GetFlushReason();
     for (auto listener : immutable_db_options_.listeners) {
       listener->OnFlushBegin(this, info);
     }
@@ -266,6 +268,7 @@ void DBImpl::NotifyOnFlushCompleted(ColumnFamilyData* cfd,
     info.smallest_seqno = file_meta->smallest_seqno;
     info.largest_seqno = file_meta->largest_seqno;
     info.table_properties = prop;
+    info.flush_reason = cfd->GetFlushReason();
     for (auto listener : immutable_db_options_.listeners) {
       listener->OnFlushCompleted(this, info);
     }
@@ -287,7 +290,7 @@ Status DBImpl::CompactRange(const CompactRangeOptions& options,
   auto cfd = cfh->cfd();
   bool exclusive = options.exclusive_manual_compaction;
 
-  Status s = FlushMemTable(cfd, FlushOptions());
+  Status s = FlushMemTable(cfd, FlushOptions(), FlushReason::kManualCompaction);
   if (!s.ok()) {
     LogFlush(immutable_db_options_.info_log);
     return s;
@@ -812,7 +815,8 @@ Status DBImpl::Flush(const FlushOptions& flush_options,
   auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(column_family);
   ROCKS_LOG_INFO(immutable_db_options_.info_log, "[%s] Manual flush start.",
                  cfh->GetName().c_str());
-  Status s = FlushMemTable(cfh->cfd(), flush_options);
+  Status s =
+      FlushMemTable(cfh->cfd(), flush_options, FlushReason::kManualCompaction);
   ROCKS_LOG_INFO(immutable_db_options_.info_log,
                  "[%s] Manual flush finished, status: %s\n",
                  cfh->GetName().c_str(), s.ToString().c_str());
@@ -949,7 +953,7 @@ Status DBImpl::RunManualCompaction(ColumnFamilyData* cfd, int input_level,
 
 Status DBImpl::FlushMemTable(ColumnFamilyData* cfd,
                              const FlushOptions& flush_options,
-                             bool writes_stopped) {
+                             FlushReason flush_reason, bool writes_stopped) {
   Status s;
   uint64_t flush_memtable_id = 0;
   {
@@ -978,7 +982,7 @@ Status DBImpl::FlushMemTable(ColumnFamilyData* cfd,
     cfd->imm()->FlushRequested();
 
     // schedule flush
-    SchedulePendingFlush(cfd);
+    SchedulePendingFlush(cfd, flush_reason);
     MaybeScheduleFlushOrCompaction();
   }
 
@@ -1134,11 +1138,12 @@ ColumnFamilyData* DBImpl::PopFirstFromCompactionQueue() {
   return cfd;
 }
 
-void DBImpl::AddToFlushQueue(ColumnFamilyData* cfd) {
+void DBImpl::AddToFlushQueue(ColumnFamilyData* cfd, FlushReason flush_reason) {
   assert(!cfd->pending_flush());
   cfd->Ref();
   flush_queue_.push_back(cfd);
   cfd->set_pending_flush(true);
+  cfd->SetFlushReason(flush_reason);
 }
 
 ColumnFamilyData* DBImpl::PopFirstFromFlushQueue() {
@@ -1147,12 +1152,14 @@ ColumnFamilyData* DBImpl::PopFirstFromFlushQueue() {
   flush_queue_.pop_front();
   assert(cfd->pending_flush());
   cfd->set_pending_flush(false);
+  // TODO: need to unset flush reason?
   return cfd;
 }
 
-void DBImpl::SchedulePendingFlush(ColumnFamilyData* cfd) {
+void DBImpl::SchedulePendingFlush(ColumnFamilyData* cfd,
+                                  FlushReason flush_reason) {
   if (!cfd->pending_flush() && cfd->imm()->IsFlushPending()) {
-    AddToFlushQueue(cfd);
+    AddToFlushQueue(cfd, flush_reason);
     ++unscheduled_flushes_;
   }
 }
@@ -1929,7 +1936,7 @@ void DBImpl::InstallSuperVersionAndScheduleWork(
 
   // Whenever we install new SuperVersion, we might need to issue new flushes or
   // compactions.
-  SchedulePendingFlush(cfd);
+  SchedulePendingFlush(cfd, FlushReason::kSuperVersionChange);
   SchedulePendingCompaction(cfd);
   MaybeScheduleFlushOrCompaction();
 

db/db_impl_debug.cc

@@ -103,7 +103,7 @@ Status DBImpl::TEST_FlushMemTable(bool wait, ColumnFamilyHandle* cfh) {
     auto cfhi = reinterpret_cast<ColumnFamilyHandleImpl*>(cfh);
     cfd = cfhi->cfd();
   }
-  return FlushMemTable(cfd, fo);
+  return FlushMemTable(cfd, fo, FlushReason::kTest);
 }
 
 Status DBImpl::TEST_WaitForFlushMemTable(ColumnFamilyHandle* column_family) {

db/db_impl_write.cc

@@ -1019,7 +1019,7 @@ Status DBImpl::SwitchWAL(WriteContext* write_context) {
         break;
       }
       cfd->imm()->FlushRequested();
-      SchedulePendingFlush(cfd);
+      SchedulePendingFlush(cfd, FlushReason::kWriteBufferManager);
     }
   }
   MaybeScheduleFlushOrCompaction();
@@ -1065,7 +1065,7 @@ Status DBImpl::HandleWriteBufferFull(WriteContext* write_context) {
     status = SwitchMemtable(cfd_picked, write_context);
     if (status.ok()) {
       cfd_picked->imm()->FlushRequested();
-      SchedulePendingFlush(cfd_picked);
+      SchedulePendingFlush(cfd_picked, FlushReason::kWriteBufferFull);
       MaybeScheduleFlushOrCompaction();
     }
   }

db/flush_job.cc

@@ -54,6 +54,32 @@
 
 namespace rocksdb {
 
+const char* GetFlushReasonString (FlushReason flush_reason) {
+  switch (flush_reason) {
+    case FlushReason::kUnknown:
+      return "Unknown";
+    case FlushReason::kGetLiveFiles:
+      return "Get Live Files";
+    case FlushReason::kShutDown:
+      return "Shut down";
+    case FlushReason::kExternalFileIngestion:
+      return "External File Ingestion";
+    case FlushReason::kManualCompaction:
+      return "Manual Compaction";
+    case FlushReason::kWriteBufferManager:
+      return "Write Buffer Manager";
+    case FlushReason::kWriteBufferFull:
+      return "Write Buffer Full";
+    case FlushReason::kTest:
+      return "Test";
+    case FlushReason::kSuperVersionChange:
+      return "SuperVersion Change";
+    default:
+      return "Invalid";
+  }
+}
+
+
 FlushJob::FlushJob(const std::string& dbname, ColumnFamilyData* cfd,
                    const ImmutableDBOptions& db_options,
                    const MutableCFOptions& mutable_cf_options,
@@ -278,12 +304,13 @@ Status FlushJob::WriteLevel0Table() {
       total_memory_usage += m->ApproximateMemoryUsage();
     }
 
-    event_logger_->Log() << "job" << job_context_->job_id << "event"
-                         << "flush_started"
-                         << "num_memtables" << mems_.size() << "num_entries"
-                         << total_num_entries << "num_deletes"
-                         << total_num_deletes << "memory_usage"
-                         << total_memory_usage;
+    event_logger_->Log()
+        << "job" << job_context_->job_id << "event"
+        << "flush_started"
+        << "num_memtables" << mems_.size() << "num_entries" << total_num_entries
+        << "num_deletes" << total_num_deletes << "memory_usage"
+        << total_memory_usage << "flush_reason"
+        << GetFlushReasonString(cfd_->GetFlushReason());
 
     {
       ScopedArenaIterator iter(

include/rocksdb/listener.h

@@ -82,6 +82,18 @@ enum class CompactionReason {
   kBottommostFiles,
 };
 
+enum class FlushReason : int {
+  kUnknown = 0x00,
+  kGetLiveFiles = 0x01,
+  kShutDown = 0x02,
+  kExternalFileIngestion = 0x03,
+  kManualCompaction = 0x04,
+  kWriteBufferManager = 0x05,
+  kWriteBufferFull = 0x06,
+  kTest = 0x07,
+  kSuperVersionChange = 0x08,
+};
+
 enum class BackgroundErrorReason {
   kFlush,
   kCompaction,
@@ -143,6 +155,8 @@ struct FlushJobInfo {
   SequenceNumber largest_seqno;
   // Table properties of the table being flushed
   TableProperties table_properties;
+
+  FlushReason flush_reason;
 };
 
 struct CompactionJobInfo {