Add DBOption.max_subcompaction to option dump

Summary:
RocksDB options can be dumped to the log file, and
up to this point the max_subcompactions option was not included
in this dump. This fixes that.

Test Plan: makek all && make check

Reviewers: MarkCallaghan, igor, noetzli, anthony, yhchiang, sdong

Reviewed By: yhchiang, sdong

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D46971

include/rocksdb/options.h

@@ -910,7 +910,7 @@ struct DBOptions {
   // Default: 1
   int max_background_compactions;
 
-  // This integer represents the maximum number of threads that will
+  // This value represents the maximum number of threads that will
   // concurrently perform a compaction job by breaking it into multiple,
   // smaller ones that are run simultaneously.
   // Default: 1 (i.e. no subcompactions)

util/options.cc

@@ -347,6 +347,8 @@ void DBOptions::Dump(Logger* log) const {
         delete_obsolete_files_period_micros);
     Warn(log, "             Options.max_background_compactions: %d",
         max_background_compactions);
+    Warn(log, "                     Options.max_subcompactions: %" PRIu32,
+        max_subcompactions);
     Warn(log, "                 Options.max_background_flushes: %d",
         max_background_flushes);
     Warn(log, "                        Options.WAL_ttl_seconds: %" PRIu64,