Add db_bench option for stderr logging

Summary:
The info log file ("LOG") is stored in the db directory by default. When the db is on a distributed env, this is unnecessarily slow. So, I added an option to db_bench to just print the info log messages to stderr.
Closes https://github.com/facebook/rocksdb/pull/1641

Differential Revision: D4309348

Pulled By: ajkr

fbshipit-source-id: 1e6f851

tools/db_bench_tool.cc

@@ -60,6 +60,7 @@
 #include "util/mutexlock.h"
 #include "util/random.h"
 #include "util/statistics.h"
+#include "util/stderr_logger.h"
 #include "util/string_util.h"
 #include "util/testutil.h"
 #include "util/transaction_test_util.h"
@@ -592,6 +593,9 @@ DEFINE_string(
 DEFINE_bool(report_bg_io_stats, false,
             "Measure times spents on I/Os while in compactions. ");
 
+DEFINE_bool(use_stderr_info_logger, false,
+            "Write info logs to stderr instead of to LOG file. ");
+
 DEFINE_bool(use_blob_db, false, "Whether to use BlobDB. ");
 
 enum rocksdb::CompressionType StringToCompressionType(const char* ctype) {
@@ -2745,6 +2749,9 @@ class Benchmark {
         exit(1);
       }
     }
+    if (FLAGS_use_stderr_info_logger) {
+      options.info_log.reset(new StderrLogger());
+    }
     options.memtable_huge_page_size = FLAGS_memtable_use_huge_page ? 2048 : 0;
     options.memtable_prefix_bloom_size_ratio = FLAGS_memtable_bloom_size_ratio;
     if (FLAGS_memtable_insert_with_hint_prefix_size > 0) {