OptimizeForSmallDb(): revert some options whose defaults were just changed

Summary: We changed default options of max_open_files and max_file_opening_threads but didn't revert it in OptimizeForSmallDb().

Test Plan: Add a unit test

Reviewers: igor, yhchiang, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: leveldb, andrewkr, dhruba

Differential Revision: https://reviews.facebook.net/D57675

include/rocksdb/options.h

@@ -824,6 +824,10 @@ struct DBOptions {
 
   // Some functions that make it easier to optimize RocksDB
 
+  // Use this if your DB is very small (like under 1GB) and you don't want to
+  // spend lots of memory for memtables.
+  DBOptions* OptimizeForSmallDb();
+
 #ifndef ROCKSDB_LITE
   // By default, RocksDB uses only one background thread for flush and
   // compaction. Calling this function will set it up such that total of
@@ -898,7 +902,7 @@ struct DBOptions {
 
   // If max_open_files is -1, DB will open all files on DB::Open(). You can
   // use this option to increase the number of threads used to open the files.
-  // Default: 1
+  // Default: 16
   int max_file_opening_threads;
 
   // Once write-ahead logs exceed this size, we will start forcing the flush of
@@ -1343,6 +1347,8 @@ struct Options : public DBOptions, public ColumnFamilyOptions {
 
   void DumpCFOptions(Logger* log) const;
 
+  // Some functions that make it easier to optimize RocksDB
+
   // Set appropriate parameters for bulk loading.
   // The reason that this is a function that returns "this" instead of a
   // constructor is to enable chaining of multiple similar calls in the future.
@@ -1352,6 +1358,10 @@ struct Options : public DBOptions, public ColumnFamilyOptions {
   // It's recommended to manually call CompactRange(NULL, NULL) before reading
   // from the database, because otherwise the read can be very slow.
   Options* PrepareForBulkLoad();
+
+  // Use this if your DB is very small (like under 1GB) and you don't want to
+  // spend lots of memory for memtables.
+  Options* OptimizeForSmallDb();
 };
 
 //

util/options.cc

@@ -668,6 +668,12 @@ Options::PrepareForBulkLoad()
   return this;
 }
 
+Options* Options::OptimizeForSmallDb() {
+  ColumnFamilyOptions::OptimizeForSmallDb();
+  DBOptions::OptimizeForSmallDb();
+  return this;
+}
+
 Options* Options::OldDefaults(int rocksdb_major_version,
                               int rocksdb_minor_version) {
   ColumnFamilyOptions::OldDefaults(rocksdb_major_version,
@@ -705,6 +711,12 @@ ColumnFamilyOptions* ColumnFamilyOptions::OldDefaults(
 }
 
 // Optimization functions
+DBOptions* DBOptions::OptimizeForSmallDb() {
+  max_file_opening_threads = 1;
+  max_open_files = 5000;
+  return this;
+}
+
 ColumnFamilyOptions* ColumnFamilyOptions::OptimizeForSmallDb() {
   write_buffer_size = 2 << 20;
   target_file_size_base = 2 * 1048576;

util/options_test.cc

@@ -1315,9 +1315,10 @@ TEST_F(OptionsParserTest, DifferentDefault) {
               old_default_cf_opts.compaction_pri);
   }
 
-  ColumnFamilyOptions cf_small_opts;
-  cf_small_opts.OptimizeForSmallDb();
-  ASSERT_EQ(2 << 20, cf_small_opts.write_buffer_size);
+  Options small_opts;
+  small_opts.OptimizeForSmallDb();
+  ASSERT_EQ(2 << 20, small_opts.write_buffer_size);
+  ASSERT_EQ(5000, small_opts.max_open_files);
 }
 
 class OptionsSanityCheckTest : public OptionsParserTest {