LRU Cache to enable mid-point insertion by default (#5508)

Summary:
Mid-point insertion is a useful feature and is mature now. Make it default. Also changed cache_index_and_filter_blocks_with_high_priority=true as default accordingly, so that we won't evict index and filter blocks easier after the change, to avoid too many surprises to users.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5508

Test Plan: Run all existing tests.

Differential Revision: D16021179

fbshipit-source-id: ce8456e8d43b3bfb48df6c304b5290a9d19817eb

HISTORY.md

 # Rocksdb Change Log
 ## Unreleased
+### Default Option Change
+* LRUCacheOptions.high_pri_pool_ratio is set to 0.5 (previously 0.0) by default, which means that by default midpoint insertion is enabled. The same change is made for the default value of high_pri_pool_ratio argument in NewLRUCache(). When block cache is not explictly created, the small block cache created by BlockBasedTable will still has this option to be 0.0.
+* Change BlockBasedTableOptions.cache_index_and_filter_blocks_with_high_priority's default value from false to true.
+
 ### Public API Change
 * Now DB::Close() will return Aborted() error when there is unreleased snapshot. Users can retry after all snapshots are released.
 * Partitions of partitioned indexes no longer affect the read amplification statistics.

cache/cache_test.cc

@@ -90,7 +90,7 @@ class CacheTest : public testing::TestWithParam<std::string> {
                                   bool strict_capacity_limit) {
     auto type = GetParam();
     if (type == kLRU) {
-      return NewLRUCache(capacity, num_shard_bits, strict_capacity_limit);
+      return NewLRUCache(capacity, num_shard_bits, strict_capacity_limit, 0.0);
     }
     if (type == kClock) {
       return NewClockCache(capacity, num_shard_bits, strict_capacity_limit);

include/rocksdb/cache.h

@@ -59,7 +59,7 @@ struct LRUCacheOptions {
   //
   // See also
   // BlockBasedTableOptions::cache_index_and_filter_blocks_with_high_priority.
-  double high_pri_pool_ratio = 0.0;
+  double high_pri_pool_ratio = 0.5;
 
   // If non-nullptr will use this allocator instead of system allocator when
   // allocating memory for cache blocks. Call this method before you start using
@@ -99,7 +99,7 @@ struct LRUCacheOptions {
 // will be at least 512KB and number of shard bits will not exceed 6.
 extern std::shared_ptr<Cache> NewLRUCache(
     size_t capacity, int num_shard_bits = -1,
-    bool strict_capacity_limit = false, double high_pri_pool_ratio = 0.0,
+    bool strict_capacity_limit = false, double high_pri_pool_ratio = 0.5,
     std::shared_ptr<MemoryAllocator> memory_allocator = nullptr,
     bool use_adaptive_mutex = kDefaultToAdaptiveMutex);
 

include/rocksdb/table.h

@@ -74,7 +74,7 @@ struct BlockBasedTableOptions {
   // blocks with high priority. If set to true, depending on implementation of
   // block cache, index and filter blocks may be less likely to be evicted
   // than data blocks.
-  bool cache_index_and_filter_blocks_with_high_priority = false;
+  bool cache_index_and_filter_blocks_with_high_priority = true;
 
   // if cache_index_and_filter_blocks is true and the below is true, then
   // filter and index blocks are stored in the cache, but a reference is

options/options_test.cc

@@ -617,8 +617,9 @@ TEST_F(OptionsTest, GetBlockBasedTableOptionsFromString) {
                 new_opt.block_cache)->GetNumShardBits(),
                 GetDefaultCacheShardBits(new_opt.block_cache->GetCapacity()));
   ASSERT_EQ(new_opt.block_cache->HasStrictCapacityLimit(), false);
-  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(
-                new_opt.block_cache)->GetHighPriPoolRatio(), 0.0);
+  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(new_opt.block_cache)
+                ->GetHighPriPoolRatio(),
+            0.5);
   ASSERT_TRUE(new_opt.block_cache_compressed != nullptr);
   ASSERT_EQ(new_opt.block_cache_compressed->GetCapacity(), 2*1024UL*1024UL);
   // Default values
@@ -627,16 +628,17 @@ TEST_F(OptionsTest, GetBlockBasedTableOptionsFromString) {
                 GetDefaultCacheShardBits(
                     new_opt.block_cache_compressed->GetCapacity()));
   ASSERT_EQ(new_opt.block_cache_compressed->HasStrictCapacityLimit(), false);
-  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(
-                new_opt.block_cache_compressed)->GetHighPriPoolRatio(),
-                0.0);
+  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(new_opt.block_cache_compressed)
+                ->GetHighPriPoolRatio(),
+            0.5);
 
   // Set couple of block cache options.
-  ASSERT_OK(GetBlockBasedTableOptionsFromString(table_opt,
-             "block_cache={num_shard_bits=5;high_pri_pool_ratio=0.5;};"
-             "block_cache_compressed={num_shard_bits=5;"
-             "high_pri_pool_ratio=0.5;}",
-             &new_opt));
+  ASSERT_OK(GetBlockBasedTableOptionsFromString(
+      table_opt,
+      "block_cache={num_shard_bits=5;high_pri_pool_ratio=0.5;};"
+      "block_cache_compressed={num_shard_bits=5;"
+      "high_pri_pool_ratio=0.0;}",
+      &new_opt));
   ASSERT_EQ(new_opt.block_cache->GetCapacity(), 0);
   ASSERT_EQ(std::dynamic_pointer_cast<ShardedCache>(
                 new_opt.block_cache)->GetNumShardBits(), 5);
@@ -648,9 +650,9 @@ TEST_F(OptionsTest, GetBlockBasedTableOptionsFromString) {
   ASSERT_EQ(std::dynamic_pointer_cast<ShardedCache>(
                 new_opt.block_cache_compressed)->GetNumShardBits(), 5);
   ASSERT_EQ(new_opt.block_cache_compressed->HasStrictCapacityLimit(), false);
-  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(
-                new_opt.block_cache_compressed)->GetHighPriPoolRatio(),
-                0.5);
+  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(new_opt.block_cache_compressed)
+                ->GetHighPriPoolRatio(),
+            0.0);
 
   // Set couple of block cache options.
   ASSERT_OK(GetBlockBasedTableOptionsFromString(table_opt,
@@ -664,16 +666,17 @@ TEST_F(OptionsTest, GetBlockBasedTableOptionsFromString) {
   ASSERT_EQ(std::dynamic_pointer_cast<ShardedCache>(
                 new_opt.block_cache)->GetNumShardBits(), 4);
   ASSERT_EQ(new_opt.block_cache->HasStrictCapacityLimit(), true);
-  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(
-                new_opt.block_cache)->GetHighPriPoolRatio(), 0.0);
+  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(new_opt.block_cache)
+                ->GetHighPriPoolRatio(),
+            0.5);
   ASSERT_TRUE(new_opt.block_cache_compressed != nullptr);
   ASSERT_EQ(new_opt.block_cache_compressed->GetCapacity(), 1024UL*1024UL);
   ASSERT_EQ(std::dynamic_pointer_cast<ShardedCache>(
                 new_opt.block_cache_compressed)->GetNumShardBits(), 4);
   ASSERT_EQ(new_opt.block_cache_compressed->HasStrictCapacityLimit(), true);
-  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(
-                new_opt.block_cache_compressed)->GetHighPriPoolRatio(),
-                0.0);
+  ASSERT_EQ(std::dynamic_pointer_cast<LRUCache>(new_opt.block_cache_compressed)
+                ->GetHighPriPoolRatio(),
+            0.5);
 }
 #endif  // !ROCKSDB_LITE
 

table/block_based/block_based_table_factory.cc

@@ -167,7 +167,12 @@ BlockBasedTableFactory::BlockBasedTableFactory(
   if (table_options_.no_block_cache) {
     table_options_.block_cache.reset();
   } else if (table_options_.block_cache == nullptr) {
-    table_options_.block_cache = NewLRUCache(8 << 20);
+    LRUCacheOptions co;
+    co.capacity = 8 << 20;
+    // It makes little sense to pay overhead for mid-point insertion while the
+    // block size is only 8MB.
+    co.high_pri_pool_ratio = 0.0;
+    table_options_.block_cache = NewLRUCache(co);
   }
   if (table_options_.block_size_deviation < 0 ||
       table_options_.block_size_deviation > 100) {

table/block_based/block_based_table_reader.cc

@@ -2626,12 +2626,11 @@ void BlockBasedTableIterator<TBlockIter, TValue>::SeekImpl(
   CheckOutOfBound();
 
   if (target) {
-    assert(
-        !Valid() ||
-        ((block_type_ == BlockType::kIndex &&
-          !table_->get_rep()->index_key_includes_seq)
-             ? (user_comparator_.Compare(ExtractUserKey(*target), key()) <= 0)
-             : (icomp_.Compare(*target, key()) <= 0)));
+    assert(!Valid() || ((block_type_ == BlockType::kIndex &&
+                         !table_->get_rep()->index_key_includes_seq)
+                            ? (user_comparator_.Compare(ExtractUserKey(*target),
+                                                        key()) <= 0)
+                            : (icomp_.Compare(*target, key()) <= 0)));
   }
 }
 
@@ -2954,8 +2953,8 @@ InternalIterator* BlockBasedTable::NewIterator(
             /*input_iter=*/nullptr, /*get_context=*/nullptr, &lookup_context),
         !skip_filters && !read_options.total_order_seek &&
             prefix_extractor != nullptr,
-        need_upper_bound_check, prefix_extractor, BlockType::kData,
-        caller, compaction_readahead_size);
+        need_upper_bound_check, prefix_extractor, BlockType::kData, caller,
+        compaction_readahead_size);
   } else {
     auto* mem =
         arena->AllocateAligned(sizeof(BlockBasedTableIterator<DataBlockIter>));
@@ -2966,8 +2965,8 @@ InternalIterator* BlockBasedTable::NewIterator(
                          &lookup_context),
         !skip_filters && !read_options.total_order_seek &&
             prefix_extractor != nullptr,
-        need_upper_bound_check, prefix_extractor, BlockType::kData,
-        caller, compaction_readahead_size);
+        need_upper_bound_check, prefix_extractor, BlockType::kData, caller,
+        compaction_readahead_size);
   }
 }
 
@@ -3125,8 +3124,8 @@ Status BlockBasedTable::Get(const ReadOptions& read_options, const Slice& key,
       DataBlockIter biter;
       uint64_t referenced_data_size = 0;
       NewDataBlockIterator<DataBlockIter>(
-          read_options, v.handle, &biter, BlockType::kData,
-          get_context, &lookup_data_block_context,
+          read_options, v.handle, &biter, BlockType::kData, get_context,
+          &lookup_data_block_context,
           /*s=*/Status(), /*prefetch_buffer*/ nullptr);
 
       if (no_io && biter.status().IsIncomplete()) {
@@ -3278,8 +3277,8 @@ void BlockBasedTable::MultiGet(const ReadOptions& read_options,
           offset = iiter->value().handle.offset();
           biter.Invalidate(Status::OK());
           NewDataBlockIterator<DataBlockIter>(
-              read_options, v.handle, &biter, BlockType::kData,
-              get_context, &lookup_data_block_context, Status(), nullptr);
+              read_options, v.handle, &biter, BlockType::kData, get_context,
+              &lookup_data_block_context, Status(), nullptr);
           reusing_block = false;
         }