Fix blob files not reclaimed after deleting all SSTs (facebook#12235)

Summary:
Fix issue facebook#12208.

After all the SSTs have been deleted, all the blob files will become unreferenced.
These files should be considered obsolete and thus, should not be saved to the vstorage.

Pull Request resolved: facebook#12235

Reviewed By: jowlyzhang

Differential Revision: D52806441

Pulled By: ltamasi

fbshipit-source-id: 62f94d4f2544ed2822c764d8ace5bf7f57efe42d

db/version_builder.cc

@@ -1073,6 +1073,12 @@ class VersionBuilder::Rep {
  const uint64_t oldest_blob_file_with_linked_ssts =
  GetMinOldestBlobFileNumber();
 
+ // If there are no blob files with linked SSTs, meaning that there are no
+ // valid blob files
+ if (oldest_blob_file_with_linked_ssts == kInvalidBlobFileNumber) {
+ return;
+ }
+
  auto process_base =
  [vstorage](const std::shared_ptr<BlobFileMetaData>& base_meta) {
  assert(base_meta);

db/version_builder_test.cc

@@ -1194,24 +1194,47 @@ TEST_F(VersionBuilderTest, SaveBlobFilesTo) {
 
  ASSERT_OK(second_builder.Apply(&second_edit));
 
- VersionStorageInfo newer_vstorage(
+ VersionStorageInfo new_vstorage_2(
  &icmp_, ucmp_, options_.num_levels, kCompactionStyleLevel, &new_vstorage,
  force_consistency_checks, EpochNumberRequirement::kMightMissing, nullptr,
  0, OffpeakTimeOption(options_.daily_offpeak_time_utc));
 
- ASSERT_OK(second_builder.SaveTo(&newer_vstorage));
+ ASSERT_OK(second_builder.SaveTo(&new_vstorage_2));
 
- UpdateVersionStorageInfo(&newer_vstorage);
+ UpdateVersionStorageInfo(&new_vstorage_2);
 
- const auto& newer_blob_files = newer_vstorage.GetBlobFiles();
+ const auto& newer_blob_files = new_vstorage_2.GetBlobFiles();
  ASSERT_EQ(newer_blob_files.size(), 2);
 
  const auto newer_meta3 =
- newer_vstorage.GetBlobFileMetaData(/* blob_file_number */ 3);
+ new_vstorage_2.GetBlobFileMetaData(/* blob_file_number */ 3);
 
  ASSERT_EQ(newer_meta3, nullptr);
 
- UnrefFilesInVersion(&newer_vstorage);
+ // Blob file #5 is referenced by table file #4, and blob file #9 is
+ // unreferenced. After deleting table file #4, all blob files will become
+ // unreferenced and will therefore be obsolete.
+ VersionBuilder third_builder(env_options, &ioptions_, table_cache,
+ &new_vstorage_2, version_set);
+ VersionEdit third_edit;
+ third_edit.DeleteFile(/* level */ 0, /* file_number */ 4);
+
+ ASSERT_OK(third_builder.Apply(&third_edit));
+
+ VersionStorageInfo new_vstorage_3(
+ &icmp_, ucmp_, options_.num_levels, kCompactionStyleLevel,
+ &new_vstorage_2, force_consistency_checks,
+ EpochNumberRequirement::kMightMissing, nullptr, 0,
+ OffpeakTimeOption(options_.daily_offpeak_time_utc));
+
+ ASSERT_OK(third_builder.SaveTo(&new_vstorage_3));
+
+ UpdateVersionStorageInfo(&new_vstorage_3);
+
+ ASSERT_TRUE(new_vstorage_3.GetBlobFiles().empty());
+
+ UnrefFilesInVersion(&new_vstorage_3);
+ UnrefFilesInVersion(&new_vstorage_2);
  UnrefFilesInVersion(&new_vstorage);
 }