[Rocksdb] Record WriteBlock Times into a histogram

Summary: Add a histogram to track WriteBlock times

Test Plan: db_bench and print

Reviewers: haobo, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D11319

include/leveldb/statistics.h

@@ -105,7 +105,8 @@ enum Histograms {
   DB_MULTIGET = 8,
   READ_BLOCK_COMPACTION_MICROS = 9,
   READ_BLOCK_GET_MICROS = 10,
-  HISTOGRAM_ENUM_MAX = 11
+  WRITE_RAW_BLOCK_MICROS = 11,
+  HISTOGRAM_ENUM_MAX = 12
 };
 
 const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
@@ -120,7 +121,8 @@ const std::vector<std::pair<Histograms, std::string>> HistogramsNameMap = {
   std::make_pair(TABLE_OPEN_IO_MICROS, "rocksdb.table.open.io.micros"),
   std::make_pair(DB_MULTIGET, "rocksdb.db.multiget.micros"),
   std::make_pair(READ_BLOCK_COMPACTION_MICROS, "rocksdb.read.block.compaction.micros"),
-  std::make_pair(READ_BLOCK_GET_MICROS, "rocksdb.read.block.get.micros")
+  std::make_pair(READ_BLOCK_GET_MICROS, "rocksdb.read.block.get.micros"),
+  std::make_pair(WRITE_RAW_BLOCK_MICROS, "rocksdb.write.raw.block.micros")
 };
 
 struct HistogramData {

table/table_builder.cc

@@ -14,6 +14,7 @@
 #include "table/format.h"
 #include "util/coding.h"
 #include "util/crc32c.h"
+#include "util/stop_watch.h"
 
 namespace leveldb {
 
@@ -231,6 +232,7 @@ void TableBuilder::WriteRawBlock(const Slice& block_contents,
                                  CompressionType type,
                                  BlockHandle* handle) {
   Rep* r = rep_;
+  StopWatch sw(r->options.env, r->options.statistics, WRITE_RAW_BLOCK_MICROS);
   handle->set_offset(r->offset);
   handle->set_size(block_contents.size());
   r->status = r->file->Append(block_contents);