Compaction filter support for (new) BlobDB (facebook#7974)

Summary:
Allow applications to implement a custom compaction filter and pass it to BlobDB.

The compaction filter's custom logic can operate on blobs.
To do so, application needs to subclass `CompactionFilter` abstract class and implement `FilterV2()` method.
Optionally, a method called `ShouldFilterBlobByKey()` can be implemented if application's custom logic rely solely
on the key to make a decision without reading the blob, thus saving extra IO. Examples can be found in
db/blob/db_blob_compaction_test.cc.

Pull Request resolved: facebook#7974

Test Plan: make check

Reviewed By: ltamasi

Differential Revision: D26509280

Pulled By: riversand963

fbshipit-source-id: 59f9ae5614c4359de32f4f2b16684193cc537b39

CMakeLists.txt

@@ -1065,6 +1065,7 @@ if(WITH_TESTS)
         db/blob/blob_file_garbage_test.cc
         db/blob/blob_file_reader_test.cc
         db/blob/db_blob_basic_test.cc
+        db/blob/db_blob_compaction_test.cc
         db/blob/db_blob_corruption_test.cc
         db/blob/db_blob_index_test.cc
         db/column_family_test.cc

HISTORY.md

@@ -7,6 +7,10 @@
 * Add a new option BlockBasedTableOptions::max_auto_readahead_size. RocksDB does auto-readahead for iterators on noticing more than two reads for a table file if user doesn't provide readahead_size. The readahead starts at 8KB and doubles on every additional read upto max_auto_readahead_size and now max_auto_readahead_size can be configured dynamically as well. Found that 256 KB readahead size provides the best performance, based on experiments, for auto readahead. Experiment data is in PR #3282. If value is set 0 then no automatic prefetching will be done by rocksdb. Also changing the value will only affect files opened after the change.
 * Add suppport to extend DB::VerifyFileChecksums API to also verify blob files checksum.
 
+### New Features
+* Support compaction filters for the new implementation of BlobDB. Add `FilterBlobByKey()` to `CompactionFilter`. Subclasses can override this method so that compaction filters can determine whether the actual blob value has to be read during compaction. Use a new `kUndetermined` in `CompactionFilter::Decision` to indicated that further action is necessary for compaction filter to make a decision.
+
+
 ## 6.18.0 (02/19/2021)
 ### Behavior Changes
 * When retryable IO error occurs during compaction, it is mapped to soft error and set the BG error. However, auto resume is not called to clean the soft error since compaction will reschedule by itself. In this change, When retryable IO error occurs during compaction, BG error is not set. User will be informed the error via EventHelper.
@@ -30,6 +34,7 @@
 * Add new Append and PositionedAppend APIs to FileSystem to bring the data verification information (data checksum information) from upper layer (e.g., WritableFileWriter) to the storage layer. In this way, the customized FileSystem is able to verify the correctness of data being written to the storage on time. Add checksum_handoff_file_types to DBOptions. User can use this option to control which file types (Currently supported file tyes: kWALFile, kTableFile, kDescriptorFile.) should use the new Append and PositionedAppend APIs to handoff the verification information. Currently, RocksDB only use crc32c to calculate the checksum for write handoff.
 * Add an option, `CompressionOptions::max_dict_buffer_bytes`, to limit the in-memory buffering for selecting samples for generating/training a dictionary. The limit is currently loosely adhered to.
 
+
 ## 6.17.0 (01/15/2021)
 ### Behavior Changes
 * When verifying full file checksum with `DB::VerifyFileChecksums()`, we now fail with `Status::InvalidArgument` if the name of the checksum generator used for verification does not match the name of the checksum generator used for protecting the file when it was created.

Makefile

@@ -592,6 +592,7 @@ ifdef ASSERT_STATUS_CHECKED
 		db_log_iter_test \
 		db_bloom_filter_test \
 		db_blob_basic_test \
+		db_blob_compaction_test \
 		db_blob_corruption_test \
 		db_blob_index_test \
 		db_block_cache_test \
@@ -1569,6 +1570,9 @@ db_basic_test: $(OBJ_DIR)/db/db_basic_test.o $(TEST_LIBRARY) $(LIBRARY)
 db_blob_basic_test: $(OBJ_DIR)/db/blob/db_blob_basic_test.o $(TEST_LIBRARY) $(LIBRARY)
 	$(AM_LINK)
 
+db_blob_compaction_test: $(OBJ_DIR)/db/blob/db_blob_compaction_test.o $(TEST_LIBRARY) $(LIBRARY)
+	$(AM_LINK)
+
 db_with_timestamp_basic_test: $(OBJ_DIR)/db/db_with_timestamp_basic_test.o $(TEST_LIBRARY) $(LIBRARY)
 	$(AM_LINK)
 

TARGETS

@@ -1149,6 +1149,13 @@ ROCKS_TESTS = [
         [],
         [],
     ],
+    [
+        "db_blob_compaction_test",
+        "db/blob/db_blob_compaction_test.cc",
+        "serial",
+        [],
+        [],
+    ],
     [
         "db_blob_corruption_test",
         "db/blob/db_blob_corruption_test.cc",

db/blob/db_blob_basic_test.cc

@@ -355,6 +355,59 @@ TEST_P(DBBlobBasicIOErrorTest, MultiGetBlobs_IOError) {
   ASSERT_TRUE(statuses[1].IsIOError());
 }
 
+namespace {
+
+class ReadBlobCompactionFilter : public CompactionFilter {
+ public:
+  ReadBlobCompactionFilter() = default;
+  const char* Name() const override {
+    return "rocksdb.compaction.filter.read.blob";
+  }
+  CompactionFilter::Decision FilterV2(
+      int /*level*/, const Slice& /*key*/, ValueType value_type,
+      const Slice& existing_value, std::string* new_value,
+      std::string* /*skip_until*/) const override {
+    if (value_type != CompactionFilter::ValueType::kValue) {
+      return CompactionFilter::Decision::kKeep;
+    }
+    assert(new_value);
+    new_value->assign(existing_value.data(), existing_value.size());
+    return CompactionFilter::Decision::kChangeValue;
+  }
+};
+
+}  // anonymous namespace
+
+TEST_P(DBBlobBasicIOErrorTest, CompactionFilterReadBlob_IOError) {
+  Options options = GetDefaultOptions();
+  options.env = fault_injection_env_.get();
+  options.enable_blob_files = true;
+  options.min_blob_size = 0;
+  options.create_if_missing = true;
+  std::unique_ptr<CompactionFilter> compaction_filter_guard(
+      new ReadBlobCompactionFilter);
+  options.compaction_filter = compaction_filter_guard.get();
+
+  DestroyAndReopen(options);
+  constexpr char key[] = "foo";
+  constexpr char blob_value[] = "foo_blob_value";
+  ASSERT_OK(Put(key, blob_value));
+  ASSERT_OK(Flush());
+
+  SyncPoint::GetInstance()->SetCallBack(sync_point_, [this](void* /* arg */) {
+    fault_injection_env_->SetFilesystemActive(false,
+                                              Status::IOError(sync_point_));
+  });
+  SyncPoint::GetInstance()->EnableProcessing();
+
+  ASSERT_TRUE(db_->CompactRange(CompactRangeOptions(), /*begin=*/nullptr,
+                                /*end=*/nullptr)
+                  .IsIOError());
+
+  SyncPoint::GetInstance()->DisableProcessing();
+  SyncPoint::GetInstance()->ClearAllCallBacks();
+}
+
 }  // namespace ROCKSDB_NAMESPACE
 
 int main(int argc, char** argv) {