[RocksDB] dump leveldb.stats periodically in LOG file.

Summary:
Added an option stats_dump_period_sec to dump leveldb.stats to LOG periodically for diagnosis.
By defauly, it's set to a very big number 3600 (1 hour).

Test Plan: make check;

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb, zshao

Differential Revision: https://reviews.facebook.net/D10761

db/db_impl.cc

@@ -162,6 +162,7 @@ DBImpl::DBImpl(const Options& options, const std::string& dbname)
       disable_delete_obsolete_files_(false),
       delete_obsolete_files_last_run_(0),
       purge_wal_files_last_run_(0),
+      last_stats_dump_time_microsec_(0),
       stall_level0_slowdown_(0),
       stall_memtable_compaction_(0),
       stall_level0_num_files_(0),
@@ -303,6 +304,24 @@ const Status DBImpl::CreateArchivalDirectory() {
   return Status::OK();
 }
 
+void DBImpl::MaybeDumpStats() {
+  mutex_.AssertHeld();
+
+  if (options_.stats_dump_period_sec != 0) {
+    const uint64_t now_micros = env_->NowMicros();
+    if (last_stats_dump_time_microsec_ +
+        options_.stats_dump_period_sec * 1000000
+        <= now_micros) {
+      last_stats_dump_time_microsec_ = now_micros;
+      mutex_.Unlock();
+      std::string stats;
+      GetProperty("leveldb.stats", &stats);
+      Log(options_.info_log, "%s", stats.c_str());
+      mutex_.Lock();
+    }
+  }
+}
+
 // Returns the list of live files in 'live' and the list
 // of all files in the filesystem in 'allfiles'.
 void DBImpl::FindObsoleteFiles(DeletionState& deletion_state) {
@@ -1253,6 +1272,8 @@ void DBImpl::BackgroundCall() {
     MaybeScheduleCompaction();
   }
   bg_cv_.SignalAll();
+
+  MaybeDumpStats();
 }
 
 Status DBImpl::BackgroundCompaction(bool* madeProgress,

db/db_impl.h

@@ -208,6 +208,10 @@ class DBImpl : public DB {
 
 
   Status ReadFirstLine(const std::string& fname, WriteBatch* const batch);
+
+  // dump leveldb.stats to LOG
+  void MaybeDumpStats();
+
   // Constant after construction
   const InternalFilterPolicy internal_filter_policy_;
   bool owns_info_log_;
@@ -272,6 +276,9 @@ class DBImpl : public DB {
   // last time when PurgeObsoleteWALFiles ran.
   uint64_t purge_wal_files_last_run_;
 
+  // last time stats were dumped to LOG
+  uint64_t last_stats_dump_time_microsec_;
+
   // These count the number of microseconds for which MakeRoomForWrite stalls.
   uint64_t stall_level0_slowdown_;
   uint64_t stall_memtable_compaction_;

include/leveldb/options.h

@@ -430,6 +430,9 @@ struct Options {
   // Default: false
   bool skip_log_error_on_recovery;
 
+  // if not zero, dump leveldb.stats to LOG every stats_dump_period_sec
+  // Default: 3600 (1 hour)
+  unsigned int stats_dump_period_sec;
 };
 
 // Options that control read operations

util/options.cc

@@ -69,7 +69,8 @@ Options::Options()
       allow_mmap_reads(false),
       allow_mmap_writes(true),
       is_fd_close_on_exec(true),
-      skip_log_error_on_recovery(false) {
+      skip_log_error_on_recovery(false),
+      stats_dump_period_sec(3600) {
 }
 
 void
@@ -192,6 +193,8 @@ Options::Dump(Logger* log) const
         is_fd_close_on_exec);
     Log(log,"              Options.skip_log_error_on_recovery: %d",
         skip_log_error_on_recovery);
+    Log(log,"                   Options.stats_dump_period_sec: %d",
+        stats_dump_period_sec);
 }   // Options::Dump
 
 //