Fix MultiGet crash when no_block_cache is set (#5991)

Summary:
This PR fixes https://github.com/facebook/rocksdb/issues/5975. In ```BlockBasedTable::RetrieveMultipleBlocks()```, we were calling ```MaybeReadBlocksAndLoadToCache()```, which is a no-op if neither uncompressed nor compressed block cache are configured.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5991

Test Plan:
1. Add unit tests that fail with the old code and pass with the new
2. make check and asan_check

Cc spetrunia

Differential Revision: D18272744

Pulled By: anand1976

fbshipit-source-id: e62fa6090d1a6adf84fcd51dfd6859b03c6aebfe

HISTORY.md

@@ -12,6 +12,9 @@ file_creation_time of the oldest SST file in the DB.
 ### Performance Improvements
 * For 64-bit hashing, RocksDB is standardizing on a slightly modified preview version of XXH3. This function is now used for many non-persisted hashes, along with fastrange64() in place of the modulus operator, and some benchmarks show a slight improvement.
 
+### Bug Fixes
+* Fix a assertion failure in MultiGe4t() when BlockBasedTableOptions::no_block_cache is true and there is no compressed block cache
+
 ## 6.5.1 (10/16/2019)
 ### Bug Fixes
 * Revert the feature "Merging iterator to avoid child iterator reseek for some cases (#5286)" since it might cause strange results when reseek happens with a different iterator upper bound.

db/db_basic_test.cc

@@ -1577,8 +1577,12 @@ class DBBasicTestWithParallelIO
     Options options = CurrentOptions();
     Random rnd(301);
     BlockBasedTableOptions table_options;
-    table_options.pin_l0_filter_and_index_blocks_in_cache = true;
     table_options.block_cache = uncompressed_cache_;
+    if (table_options.block_cache == nullptr) {
+      table_options.no_block_cache = true;
+    } else {
+      table_options.pin_l0_filter_and_index_blocks_in_cache = true;
+    }
     table_options.block_cache_compressed = compressed_cache_;
     table_options.flush_block_policy_factory.reset(
         new MyFlushBlockPolicyFactory());
@@ -1614,6 +1618,9 @@ class DBBasicTestWithParallelIO
   int num_inserts_compressed() { return compressed_cache_->num_inserts(); }
 
   bool fill_cache() { return fill_cache_; }
+  bool compression_enabled() { return compression_enabled_; }
+  bool has_compressed_cache() { return compressed_cache_ != nullptr; }
+  bool has_uncompressed_cache() { return uncompressed_cache_ != nullptr; }
 
   static void SetUpTestCase() {}
   static void TearDownTestCase() {}
@@ -1788,7 +1795,16 @@ TEST_P(DBBasicTestWithParallelIO, MultiGet) {
   ASSERT_TRUE(CheckValue(1, values[0].ToString()));
   ASSERT_TRUE(CheckValue(51, values[1].ToString()));
 
-  int expected_reads = random_reads + (fill_cache() ? 0 : 2);
+  bool read_from_cache = false;
+  if (fill_cache()) {
+    if (has_uncompressed_cache()) {
+      read_from_cache = true;
+    } else if (has_compressed_cache() && compression_enabled()) {
+      read_from_cache = true;
+    }
+  }
+
+  int expected_reads = random_reads + (read_from_cache ? 0 : 2);
   ASSERT_EQ(env_->random_read_counter_.Read(), expected_reads);
 
   keys.resize(10);
@@ -1806,7 +1822,7 @@ TEST_P(DBBasicTestWithParallelIO, MultiGet) {
     ASSERT_OK(statuses[i]);
     ASSERT_TRUE(CheckValue(key_ints[i], values[i].ToString()));
   }
-  expected_reads += (fill_cache() ? 2 : 4);
+  expected_reads += (read_from_cache ? 2 : 4);
   ASSERT_EQ(env_->random_read_counter_.Read(), expected_reads);
 }
 
@@ -1817,12 +1833,8 @@ INSTANTIATE_TEST_CASE_P(
     // Param 1 - Uncompressed cache enabled
     // Param 2 - Data compression enabled
     // Param 3 - ReadOptions::fill_cache
-    ::testing::Values(std::make_tuple(false, true, true, true),
-                      std::make_tuple(true, true, true, true),
-                      std::make_tuple(false, true, false, true),
-                      std::make_tuple(false, true, true, false),
-                      std::make_tuple(true, true, true, false),
-                      std::make_tuple(false, true, false, false)));
+    ::testing::Combine(::testing::Bool(), ::testing::Bool(),
+                       ::testing::Bool(), ::testing::Bool()));
 
 class DBBasicTestWithTimestampWithParam
     : public DBTestBase,

table/block_based/block_based_table_reader.cc

@@ -2398,34 +2398,42 @@ void BlockBasedTable::RetrieveMultipleBlocks(
             nullptr, options, handle, uncompression_dict, block_entry,
             BlockType::kData, mget_iter->get_context,
             &lookup_data_block_context, &raw_block_contents);
+
+        // block_entry value could be null if no block cache is present, i.e
+        // BlockBasedTableOptions::no_block_cache is true and no compressed
+        // block cache is configured. In that case, fall
+        // through and set up the block explicitly
+        if (block_entry->GetValue() != nullptr) {
+          continue;
+        }
+      }
+
+      CompressionType compression_type =
+          raw_block_contents.get_compression_type();
+      BlockContents contents;
+      if (compression_type != kNoCompression) {
+        UncompressionContext context(compression_type);
+        UncompressionInfo info(context, uncompression_dict, compression_type);
+        s = UncompressBlockContents(info, req.result.data(), handle.size(),
+                                    &contents, footer.version(),
+                                    rep_->ioptions, memory_allocator);
       } else {
-        CompressionType compression_type =
-            raw_block_contents.get_compression_type();
-        BlockContents contents;
-        if (compression_type != kNoCompression) {
-          UncompressionContext context(compression_type);
-          UncompressionInfo info(context, uncompression_dict, compression_type);
-          s = UncompressBlockContents(info, req.result.data(), handle.size(),
-                                      &contents, footer.version(),
-                                      rep_->ioptions, memory_allocator);
+        if (scratch != nullptr) {
+          // If we used the scratch buffer, then the contents need to be
+          // copied to heap
+          Slice raw = Slice(req.result.data(), handle.size());
+          contents = BlockContents(
+              CopyBufferToHeap(GetMemoryAllocator(rep_->table_options), raw),
+              handle.size());
         } else {
-          if (scratch != nullptr) {
-            // If we used the scratch buffer, then the contents need to be
-            // copied to heap
-            Slice raw = Slice(req.result.data(), handle.size());
-            contents = BlockContents(
-                CopyBufferToHeap(GetMemoryAllocator(rep_->table_options), raw),
-                handle.size());
-          } else {
-            contents = std::move(raw_block_contents);
-          }
-        }
-        if (s.ok()) {
-          (*results)[idx_in_batch].SetOwnedValue(
-              new Block(std::move(contents), global_seqno,
-                        read_amp_bytes_per_bit, ioptions.statistics));
+          contents = std::move(raw_block_contents);
         }
       }
+      if (s.ok()) {
+        (*results)[idx_in_batch].SetOwnedValue(
+            new Block(std::move(contents), global_seqno,
+                      read_amp_bytes_per_bit, ioptions.statistics));
+      }
     }
     (*statuses)[idx_in_batch] = s;
   }