Refactor and clean up the code that reads a blob from a file (#6093)

Summary:
This patch factors out the logic that reads a (potentially compressed) blob
from a file into a separate helper method `GetRawBlobFromFile`, and cleans
up the code a bit. Also, errors during decompression are now logged/propagated
to the user by returning a `Status` code of `Corruption`.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/6093

Test Plan: `make check`

Differential Revision: D18716673

Pulled By: ltamasi

fbshipit-source-id: 44144bc064cab616862d5643f34384f2bae6eb78

utilities/blob_db/blob_db_impl.cc

@@ -1251,15 +1251,18 @@ bool BlobDBImpl::SetSnapshotIfNeeded(ReadOptions* read_options) {
 
 Status BlobDBImpl::GetBlobValue(const Slice& key, const Slice& index_entry,
                                 PinnableSlice* value, uint64_t* expiration) {
-  assert(value != nullptr);
+  assert(value);
+
   BlobIndex blob_index;
   Status s = blob_index.DecodeFrom(index_entry);
   if (!s.ok()) {
     return s;
   }
+
   if (blob_index.HasTTL() && blob_index.expiration() <= EpochNow()) {
     return Status::NotFound("Key expired");
   }
+
   if (expiration != nullptr) {
     if (blob_index.HasTTL()) {
       *expiration = blob_index.expiration();
@@ -1267,13 +1270,65 @@ Status BlobDBImpl::GetBlobValue(const Slice& key, const Slice& index_entry,
       *expiration = kNoExpiration;
     }
   }
+
   if (blob_index.IsInlined()) {
     // TODO(yiwu): If index_entry is a PinnableSlice, we can also pin the same
     // memory buffer to avoid extra copy.
     value->PinSelf(blob_index.value());
     return Status::OK();
   }
-  if (blob_index.size() == 0) {
+
+  CompressionType compression_type = kNoCompression;
+  s = GetRawBlobFromFile(key, blob_index.file_number(), blob_index.offset(),
+                         blob_index.size(), value, &compression_type);
+  if (!s.ok()) {
+    return s;
+  }
+
+  if (compression_type != kNoCompression) {
+    BlockContents contents;
+    auto cfh = static_cast<ColumnFamilyHandleImpl*>(DefaultColumnFamily());
+
+    {
+      StopWatch decompression_sw(env_, statistics_,
+                                 BLOB_DB_DECOMPRESSION_MICROS);
+      UncompressionContext context(compression_type);
+      UncompressionInfo info(context, UncompressionDict::GetEmptyDict(),
+                             compression_type);
+      s = UncompressBlockContentsForCompressionType(
+          info, value->data(), value->size(), &contents,
+          kBlockBasedTableVersionFormat, *(cfh->cfd()->ioptions()));
+    }
+
+    if (!s.ok()) {
+      if (debug_level_ >= 2) {
+        ROCKS_LOG_ERROR(
+            db_options_.info_log,
+            "Uncompression error during blob read from file: %" PRIu64
+            " blob_offset: %" PRIu64 " blob_size: %" PRIu64
+            " key: %s status: '%s'",
+            blob_index.file_number(), blob_index.offset(), blob_index.size(),
+            key.ToString(/* output_hex */ true).c_str(), s.ToString().c_str());
+      }
+
+      return Status::Corruption("Unable to uncompress blob.");
+    }
+
+    value->PinSelf(contents.data);
+  }
+
+  return Status::OK();
+}
+
+Status BlobDBImpl::GetRawBlobFromFile(const Slice& key, uint64_t file_number,
+                                      uint64_t offset, uint64_t size,
+                                      PinnableSlice* value,
+                                      CompressionType* compression_type) {
+  assert(value);
+  assert(compression_type);
+  assert(*compression_type == kNoCompression);
+
+  if (!size) {
     value->PinSelf("");
     return Status::OK();
   }
@@ -1281,47 +1336,46 @@ Status BlobDBImpl::GetBlobValue(const Slice& key, const Slice& index_entry,
   // offset has to have certain min, as we will read CRC
   // later from the Blob Header, which needs to be also a
   // valid offset.
-  if (blob_index.offset() <
+  if (offset <
       (BlobLogHeader::kSize + BlobLogRecord::kHeaderSize + key.size())) {
     if (debug_level_ >= 2) {
       ROCKS_LOG_ERROR(db_options_.info_log,
                       "Invalid blob index file_number: %" PRIu64
                       " blob_offset: %" PRIu64 " blob_size: %" PRIu64
                       " key: %s",
-                      blob_index.file_number(), blob_index.offset(),
-                      blob_index.size(), key.data());
+                      file_number, offset, size,
+                      key.ToString(/* output_hex */ true).c_str());
     }
+
     return Status::NotFound("Invalid blob offset");
   }
 
-  std::shared_ptr<BlobFile> bfile;
+  std::shared_ptr<BlobFile> blob_file;
+
   {
     ReadLock rl(&mutex_);
-    auto hitr = blob_files_.find(blob_index.file_number());
+    auto it = blob_files_.find(file_number);
 
     // file was deleted
-    if (hitr == blob_files_.end()) {
+    if (it == blob_files_.end()) {
       return Status::NotFound("Blob Not Found as blob file missing");
     }
 
-    bfile = hitr->second;
+    blob_file = it->second;
   }
 
-  if (blob_index.size() == 0 && value != nullptr) {
-    value->PinSelf("");
-    return Status::OK();
-  }
+  *compression_type = blob_file->compression();
 
   // takes locks when called
   std::shared_ptr<RandomAccessFileReader> reader;
-  s = GetBlobFileReader(bfile, &reader);
+  Status s = GetBlobFileReader(blob_file, &reader);
   if (!s.ok()) {
     return s;
   }
 
-  assert(blob_index.offset() > key.size() + sizeof(uint32_t));
-  uint64_t record_offset = blob_index.offset() - key.size() - sizeof(uint32_t);
-  uint64_t record_size = sizeof(uint32_t) + key.size() + blob_index.size();
+  assert(offset >= key.size() + sizeof(uint32_t));
+  const uint64_t record_offset = offset - key.size() - sizeof(uint32_t);
+  const uint64_t record_size = sizeof(uint32_t) + key.size() + size;
 
   // Allocate the buffer. This is safe in C++11
   std::string buffer_str(static_cast<size_t>(record_size), static_cast<char>(0));
@@ -1329,42 +1383,44 @@ Status BlobDBImpl::GetBlobValue(const Slice& key, const Slice& index_entry,
 
   // A partial blob record contain checksum, key and value.
   Slice blob_record;
+
   {
     StopWatch read_sw(env_, statistics_, BLOB_DB_BLOB_FILE_READ_MICROS);
     s = reader->Read(record_offset, static_cast<size_t>(record_size), &blob_record, buffer);
     RecordTick(statistics_, BLOB_DB_BLOB_FILE_BYTES_READ, blob_record.size());
   }
+
   if (!s.ok()) {
-    ROCKS_LOG_DEBUG(db_options_.info_log,
-                    "Failed to read blob from blob file %" PRIu64
-                    ", blob_offset: %" PRIu64 ", blob_size: %" PRIu64
-                    ", key_size: %" ROCKSDB_PRIszt ", status: '%s'",
-                    bfile->BlobFileNumber(), blob_index.offset(),
-                    blob_index.size(), key.size(), s.ToString().c_str());
+    ROCKS_LOG_DEBUG(
+        db_options_.info_log,
+        "Failed to read blob from blob file %" PRIu64 ", blob_offset: %" PRIu64
+        ", blob_size: %" PRIu64 ", key_size: %" ROCKSDB_PRIszt ", status: '%s'",
+        file_number, offset, size, key.size(), s.ToString().c_str());
     return s;
   }
+
   if (blob_record.size() != record_size) {
     ROCKS_LOG_DEBUG(
         db_options_.info_log,
         "Failed to read blob from blob file %" PRIu64 ", blob_offset: %" PRIu64
         ", blob_size: %" PRIu64 ", key_size: %" ROCKSDB_PRIszt
         ", read %" ROCKSDB_PRIszt " bytes, expected %" PRIu64 " bytes",
-        bfile->BlobFileNumber(), blob_index.offset(), blob_index.size(),
-        key.size(), blob_record.size(), record_size);
+        file_number, offset, size, key.size(), blob_record.size(), record_size);
 
     return Status::Corruption("Failed to retrieve blob from blob index.");
   }
+
   Slice crc_slice(blob_record.data(), sizeof(uint32_t));
   Slice blob_value(blob_record.data() + sizeof(uint32_t) + key.size(),
-                   static_cast<size_t>(blob_index.size()));
-  uint32_t crc_exp;
+                   static_cast<size_t>(size));
+
+  uint32_t crc_exp = 0;
   if (!GetFixed32(&crc_slice, &crc_exp)) {
-    ROCKS_LOG_DEBUG(db_options_.info_log,
-                    "Unable to decode CRC from blob file %" PRIu64
-                    ", blob_offset: %" PRIu64 ", blob_size: %" PRIu64
-                    ", key size: %" ROCKSDB_PRIszt ", status: '%s'",
-                    bfile->BlobFileNumber(), blob_index.offset(),
-                    blob_index.size(), key.size(), s.ToString().c_str());
+    ROCKS_LOG_DEBUG(
+        db_options_.info_log,
+        "Unable to decode CRC from blob file %" PRIu64 ", blob_offset: %" PRIu64
+        ", blob_size: %" PRIu64 ", key size: %" ROCKSDB_PRIszt ", status: '%s'",
+        file_number, offset, size, key.size(), s.ToString().c_str());
     return Status::Corruption("Unable to decode checksum.");
   }
 
@@ -1373,34 +1429,20 @@ Status BlobDBImpl::GetBlobValue(const Slice& key, const Slice& index_entry,
   crc = crc32c::Mask(crc);  // Adjust for storage
   if (crc != crc_exp) {
     if (debug_level_ >= 2) {
-      ROCKS_LOG_ERROR(db_options_.info_log,
-                      "Blob crc mismatch file: %s blob_offset: %" PRIu64
-                      " blob_size: %" PRIu64 " key: %s status: '%s'",
-                      bfile->PathName().c_str(), blob_index.offset(),
-                      blob_index.size(), key.data(), s.ToString().c_str());
+      ROCKS_LOG_ERROR(
+          db_options_.info_log,
+          "Blob crc mismatch file: %" PRIu64 " blob_offset: %" PRIu64
+          " blob_size: %" PRIu64 " key: %s status: '%s'",
+          file_number, offset, size,
+          key.ToString(/* output_hex */ true).c_str(), s.ToString().c_str());
     }
+
     return Status::Corruption("Corruption. Blob CRC mismatch");
   }
 
-  if (bfile->compression() == kNoCompression) {
-    value->PinSelf(blob_value);
-  } else {
-    BlockContents contents;
-    auto cfh = reinterpret_cast<ColumnFamilyHandleImpl*>(DefaultColumnFamily());
-    {
-      StopWatch decompression_sw(env_, statistics_,
-                                 BLOB_DB_DECOMPRESSION_MICROS);
-      UncompressionContext context(bfile->compression());
-      UncompressionInfo info(context, UncompressionDict::GetEmptyDict(),
-                             bfile->compression());
-      s = UncompressBlockContentsForCompressionType(
-          info, blob_value.data(), blob_value.size(), &contents,
-          kBlockBasedTableVersionFormat, *(cfh->cfd()->ioptions()));
-    }
-    value->PinSelf(contents.data);
-  }
+  value->PinSelf(blob_value);
 
-  return s;
+  return Status::OK();
 }
 
 Status BlobDBImpl::Get(const ReadOptions& read_options,

utilities/blob_db/blob_db_impl.h

@@ -237,6 +237,11 @@ class BlobDBImpl : public BlobDB {
   Status GetBlobValue(const Slice& key, const Slice& index_entry,
                       PinnableSlice* value, uint64_t* expiration = nullptr);
 
+  Status GetRawBlobFromFile(const Slice& key, uint64_t file_number,
+                            uint64_t offset, uint64_t size,
+                            PinnableSlice* value,
+                            CompressionType* compression_type);
+
   Slice GetCompressedSlice(const Slice& raw,
                            std::string* compression_output) const;