Change default number of cache shard bit to be 6 and max_file_opening_threads to be 16.

Summary: Cache shard bit 4 is sometimes too small and 6 is a more common value picked by users. Make that default. It shouldn't hurt much to change options.max_file_opening_threads default to be 16, which will reduce the worst case DB open time.

Test Plan: Run all existing tests.

Reviewers: IslamAbdelRahman, yhchiang, kradhakrishnan, igor, andrewkr

Reviewed By: andrewkr

Subscribers: andrewkr, MarkCallaghan, leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D55047

DEFAULT_OPTIONS_HISTORY.md

@@ -4,3 +4,5 @@
 * options.max_bytes_for_level_base changes from 10MB to 256MB
 * options.soft_pending_compaction_bytes_limit changes from 0 (disabled) to 64GB
 * options.hard_pending_compaction_bytes_limit changes from 0 (disabled) to 256GB
+* table_cache_numshardbits changes from 4 to 6
+* max_file_opening_threads changes from 1 to 16 

table/table_test.cc

@@ -1065,7 +1065,7 @@ void PrefetchRange(TableConstructor* c, Options* opt,
                    const std::vector<std::string>& keys_not_in_cache,
                    const Status expected_status = Status::OK()) {
   // reset the cache and reopen the table
-  table_options->block_cache = NewLRUCache(16 * 1024 * 1024);
+  table_options->block_cache = NewLRUCache(16 * 1024 * 1024, 4);
   opt->table_factory.reset(NewBlockBasedTableFactory(*table_options));
   const ImmutableCFOptions ioptions2(*opt);
   ASSERT_OK(c->Reopen(ioptions2));
@@ -1094,7 +1094,7 @@ TEST_F(BlockBasedTableTest, PrefetchTest) {
   BlockBasedTableOptions table_options;
   table_options.block_size = 1024;
   // big enough so we don't ever lose cached values.
-  table_options.block_cache = NewLRUCache(16 * 1024 * 1024);
+  table_options.block_cache = NewLRUCache(16 * 1024 * 1024, 4);
   opt.table_factory.reset(NewBlockBasedTableFactory(table_options));
 
   TableConstructor c(BytewiseComparator());
@@ -1328,7 +1328,7 @@ TEST_F(TableTest, HashIndexTest) {
   table_options.index_type = BlockBasedTableOptions::kHashSearch;
   table_options.hash_index_allow_collision = true;
   table_options.block_size = 1700;
-  table_options.block_cache = NewLRUCache(1024);
+  table_options.block_cache = NewLRUCache(1024, 4);
   options.table_factory.reset(NewBlockBasedTableFactory(table_options));
 
   std::unique_ptr<InternalKeyComparator> comparator(
@@ -1550,7 +1550,7 @@ TEST_F(BlockBasedTableTest, BlockCacheDisabledTest) {
   options.create_if_missing = true;
   options.statistics = CreateDBStatistics();
   BlockBasedTableOptions table_options;
-  table_options.block_cache = NewLRUCache(1024);
+  table_options.block_cache = NewLRUCache(1024, 4);
   table_options.filter_policy.reset(NewBloomFilterPolicy(10));
   options.table_factory.reset(new BlockBasedTableFactory(table_options));
   std::vector<std::string> keys;
@@ -1596,7 +1596,7 @@ TEST_F(BlockBasedTableTest, FilterBlockInBlockCache) {
 
   // Enable the cache for index/filter blocks
   BlockBasedTableOptions table_options;
-  table_options.block_cache = NewLRUCache(1024);
+  table_options.block_cache = NewLRUCache(1024, 4);
   table_options.cache_index_and_filter_blocks = true;
   options.table_factory.reset(new BlockBasedTableFactory(table_options));
   std::vector<std::string> keys;
@@ -1679,7 +1679,7 @@ TEST_F(BlockBasedTableTest, FilterBlockInBlockCache) {
   // -- PART 2: Open with very small block cache
   // In this test, no block will ever get hit since the block cache is
   // too small to fit even one entry.
-  table_options.block_cache = NewLRUCache(1);
+  table_options.block_cache = NewLRUCache(1, 4);
   options.statistics = CreateDBStatistics();
   options.table_factory.reset(new BlockBasedTableFactory(table_options));
   const ImmutableCFOptions ioptions2(options);
@@ -1719,7 +1719,7 @@ TEST_F(BlockBasedTableTest, FilterBlockInBlockCache) {
   c.ResetTableReader();
 
   // -- PART 3: Open table with bloom filter enabled but not in SST file
-  table_options.block_cache = NewLRUCache(4096);
+  table_options.block_cache = NewLRUCache(4096, 4);
   table_options.cache_index_and_filter_blocks = false;
   options.table_factory.reset(NewBlockBasedTableFactory(table_options));
 
@@ -1881,7 +1881,7 @@ TEST_F(BlockBasedTableTest, BlockCacheLeak) {
   BlockBasedTableOptions table_options;
   table_options.block_size = 1024;
   // big enough so we don't ever lose cached values.
-  table_options.block_cache = NewLRUCache(16 * 1024 * 1024);
+  table_options.block_cache = NewLRUCache(16 * 1024 * 1024, 4);
   opt.table_factory.reset(NewBlockBasedTableFactory(table_options));
 
   TableConstructor c(BytewiseComparator());
@@ -1915,7 +1915,7 @@ TEST_F(BlockBasedTableTest, BlockCacheLeak) {
   c.ResetTableReader();
 
   // rerun with different block cache
-  table_options.block_cache = NewLRUCache(16 * 1024 * 1024);
+  table_options.block_cache = NewLRUCache(16 * 1024 * 1024, 4);
   opt.table_factory.reset(NewBlockBasedTableFactory(table_options));
   const ImmutableCFOptions ioptions2(opt);
   ASSERT_OK(c.Reopen(ioptions2));

util/cache.cc

@@ -520,7 +520,7 @@ void LRUCache::Erase(const Slice& key, uint32_t hash) {
   }
 }
 
-static int kNumShardBits = 4;          // default values, can be overridden
+static int kNumShardBits = 6;  // default values, can be overridden
 
 class ShardedLRUCache : public Cache {
  private:

util/options.cc

@@ -221,7 +221,7 @@ DBOptions::DBOptions()
       info_log_level(DEBUG_LEVEL),
 #endif  // NDEBUG
       max_open_files(5000),
-      max_file_opening_threads(1),
+      max_file_opening_threads(16),
       max_total_wal_size(0),
       statistics(nullptr),
       disableDataSync(false),
@@ -238,7 +238,7 @@ DBOptions::DBOptions()
       keep_log_file_num(1000),
       recycle_log_file_num(0),
       max_manifest_file_size(std::numeric_limits<uint64_t>::max()),
-      table_cache_numshardbits(4),
+      table_cache_numshardbits(6),
       WAL_ttl_seconds(0),
       WAL_size_limit_MB(0),
       manifest_preallocation_size(4 * 1024 * 1024),
@@ -673,6 +673,8 @@ Options* Options::OldDefaults(int rocksdb_major_version,
 
 DBOptions* DBOptions::OldDefaults(int rocksdb_major_version,
                                   int rocksdb_minor_version) {
+  max_file_opening_threads = 1;
+  table_cache_numshardbits = 4;
   return this;
 }
 

util/options_test.cc

@@ -1270,6 +1270,7 @@ TEST_F(OptionsParserTest, DifferentDefault) {
   Options old_default_opts46;
   old_default_opts46.OldDefaults();
   ASSERT_EQ(10 * 1048576, old_default_opts46.max_bytes_for_level_base);
+  ASSERT_EQ(4, old_default_opts46.table_cache_numshardbits);
 
   ColumnFamilyOptions old_default_cf_opts;
   old_default_cf_opts.OldDefaults();