rocksdb/db/blob/blob_source.cc

//  Copyright (c) Meta Platforms, Inc. and affiliates.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).

#include "db/blob/blob_source.h"

#include <cassert>
#include <string>

#include "cache/cache_reservation_manager.h"
#include "cache/charged_cache.h"
#include "db/blob/blob_contents.h"
#include "db/blob/blob_file_reader.h"
#include "db/blob/blob_gen2_format.h"
#include "db/blob/blob_log_format.h"
#include "file/random_access_file_reader.h"
#include "memory/memory_allocator_impl.h"
#include "monitoring/statistics_impl.h"
#include "options/cf_options.h"
#include "table/get_context.h"
#include "table/multiget_context.h"

namespace ROCKSDB_NAMESPACE {

namespace {

Status AppendBlobRefreshRetryFailure(const Status& stale_status,
                                     const Status& retry_status) {
  assert(stale_status.IsCorruption());
  assert(!retry_status.ok());
  if (retry_status.IsCorruption()) {
    return retry_status;
  }
  return Status::CopyAppendMessage(
      stale_status, "; refresh retry failed: ", retry_status.ToString());
}

}  // namespace

BlobSource::BlobSource(const ImmutableOptions& immutable_options,
                       const MutableCFOptions& mutable_cf_options,
                       const std::string& db_id,
                       const std::string& db_session_id,
                       BlobFileCache* blob_file_cache)
    : db_id_(db_id),
      db_session_id_(db_session_id),
      statistics_(immutable_options.statistics.get()),
      blob_file_cache_(blob_file_cache),
      blob_cache_(immutable_options.blob_cache),
      lowest_used_cache_tier_(immutable_options.lowest_used_cache_tier) {
  auto bbto =
      mutable_cf_options.table_factory->GetOptions<BlockBasedTableOptions>();
  if (bbto &&
      bbto->cache_usage_options.options_overrides.at(CacheEntryRole::kBlobCache)
              .charged == CacheEntryRoleOptions::Decision::kEnabled) {
    blob_cache_ = SharedCacheInterface{std::make_shared<ChargedCache>(
        immutable_options.blob_cache, bbto->block_cache)};
  }
}

BlobSource::~BlobSource() = default;

Status BlobSource::GetBlobFromCache(
    const Slice& cache_key, CacheHandleGuard<BlobContents>* cached_blob) const {
  assert(blob_cache_);
  assert(!cache_key.empty());
  assert(cached_blob);
  assert(cached_blob->IsEmpty());

  Cache::Handle* cache_handle = nullptr;
  cache_handle = GetEntryFromCache(cache_key);
  if (cache_handle != nullptr) {
    *cached_blob =
        CacheHandleGuard<BlobContents>(blob_cache_.get(), cache_handle);

    assert(cached_blob->GetValue());

    PERF_COUNTER_ADD(blob_cache_hit_count, 1);
    PERF_COUNTER_ADD(blob_cache_read_byte, cached_blob->GetValue()->size());
    RecordTick(statistics_, BLOB_DB_CACHE_HIT);
    RecordTick(statistics_, BLOB_DB_CACHE_BYTES_READ,
               cached_blob->GetValue()->size());

    return Status::OK();
  }

  RecordTick(statistics_, BLOB_DB_CACHE_MISS);

  return Status::NotFound("Blob not found in cache");
}

Status BlobSource::PutBlobIntoCache(
    const Slice& cache_key, std::unique_ptr<BlobContents>* blob,
    CacheHandleGuard<BlobContents>* cached_blob) const {
  assert(blob_cache_);
  assert(!cache_key.empty());
  assert(blob);
  assert(*blob);
  assert(cached_blob);
  assert(cached_blob->IsEmpty());

  TypedHandle* cache_handle = nullptr;
  const Status s = InsertEntryIntoCache(cache_key, blob->get(), &cache_handle,
                                        Cache::Priority::BOTTOM);
  if (s.ok()) {
    blob->release();

    assert(cache_handle != nullptr);
    *cached_blob =
        CacheHandleGuard<BlobContents>(blob_cache_.get(), cache_handle);

    assert(cached_blob->GetValue());

    RecordTick(statistics_, BLOB_DB_CACHE_ADD);
    RecordTick(statistics_, BLOB_DB_CACHE_BYTES_WRITE,
               cached_blob->GetValue()->size());

  } else {
    RecordTick(statistics_, BLOB_DB_CACHE_ADD_FAILURES);
  }

  return s;
}

BlobSource::TypedHandle* BlobSource::GetEntryFromCache(const Slice& key) const {
  return blob_cache_.LookupFull(key, nullptr /* context */,
                                Cache::Priority::BOTTOM, statistics_,
                                lowest_used_cache_tier_);
}

void BlobSource::PinCachedBlob(CacheHandleGuard<BlobContents>* cached_blob,
                               PinnableSlice* value) {
  assert(cached_blob);
  assert(cached_blob->GetValue());
  assert(value);

  // To avoid copying the cached blob into the buffer provided by the
  // application, we can simply transfer ownership of the cache handle to
  // the target PinnableSlice. This has the potential to save a lot of
  // CPU, especially with large blob values.

  value->Reset();

  constexpr Cleanable* cleanable = nullptr;
  value->PinSlice(cached_blob->GetValue()->data(), cleanable);

  cached_blob->TransferTo(value);
}

void BlobSource::PinOwnedBlob(std::unique_ptr<BlobContents>* owned_blob,
                              PinnableSlice* value) {
  assert(owned_blob);
  assert(*owned_blob);
  assert(value);

  BlobContents* const blob = owned_blob->release();
  assert(blob);

  value->Reset();
  value->PinSlice(
      blob->data(),
      [](void* arg1, void* /* arg2 */) {
        delete static_cast<BlobContents*>(arg1);
      },
      blob, nullptr);
}

Status BlobSource::InsertEntryIntoCache(const Slice& key, BlobContents* value,
                                        TypedHandle** cache_handle,
                                        Cache::Priority priority) const {
  return blob_cache_.InsertFull(key, value, value->ApproximateMemoryUsage(),
                                cache_handle, priority,
                                lowest_used_cache_tier_);
}

Status BlobSource::GetBlob(const ReadOptions& read_options,
                           const Slice& user_key, uint64_t file_number,
                           uint64_t offset, uint64_t file_size,
                           uint64_t value_size,
                           CompressionType compression_type,
                           FilePrefetchBuffer* prefetch_buffer,
                           PinnableSlice* value, uint64_t* bytes_read) {
  assert(value);

  Status s;

  const CacheKey cache_key = GetCacheKey(file_number, file_size, offset);

  CacheHandleGuard<BlobContents> blob_handle;

  // First, try to get the blob from the cache
  //
  // If blob cache is enabled, we'll try to read from it.
  if (blob_cache_) {
    Slice key = cache_key.AsSlice();
    s = GetBlobFromCache(key, &blob_handle);
    if (s.ok()) {
      PinCachedBlob(&blob_handle, value);

      // For consistency, the size of on-disk (possibly compressed) blob record
      // is assigned to bytes_read.
      uint64_t adjustment =
          read_options.verify_checksums
              ? BlobLogRecord::CalculateAdjustmentForRecordHeader(
                    user_key.size())
              : 0;
      assert(offset >= adjustment);

      uint64_t record_size = value_size + adjustment;
      if (bytes_read) {
        *bytes_read = record_size;
      }
      return s;
    }
  }

  assert(blob_handle.IsEmpty());

  const bool no_io = read_options.read_tier == kBlockCacheTier;
  if (no_io) {
    s = Status::Incomplete("Cannot read blob(s): no disk I/O allowed");
    return s;
  }

  // Can't find the blob from the cache. Since I/O is allowed, read from the
  // file.
  std::unique_ptr<BlobContents> blob_contents;

  {
    CacheHandleGuard<BlobFileReader> blob_file_reader;
    s = blob_file_cache_->GetBlobFileReader(read_options, file_number,
                                            &blob_file_reader);
    if (!s.ok()) {
      return s;
    }

    assert(blob_file_reader.GetValue());

    if (compression_type != blob_file_reader.GetValue()->GetCompressionType()) {
      return Status::Corruption("Compression type mismatch when reading blob");
    }

    MemoryAllocator* const allocator =
        (blob_cache_ && read_options.fill_cache)
            ? blob_cache_.get()->memory_allocator()
            : nullptr;

    uint64_t read_size = 0;
    s = blob_file_reader.GetValue()->GetBlob(
        read_options, user_key, offset, value_size, compression_type,
        prefetch_buffer, allocator, &blob_contents, &read_size);
    if (s.IsCorruption()) {
      const Status stale_status = s;
      blob_file_reader.Reset();
      blob_file_cache_->Evict(file_number);

      std::unique_ptr<BlobFileReader> fresh_reader;
      s = blob_file_cache_->OpenBlobFileReaderUncached(
          read_options, file_number, &fresh_reader,
          /*allow_footer_skip_retry=*/false);
      if (!s.ok()) {
        return AppendBlobRefreshRetryFailure(stale_status, s);
      }

      if (compression_type != fresh_reader->GetCompressionType()) {
        return Status::Corruption(
            "Compression type mismatch when reading blob");
      }

      blob_contents.reset();
      read_size = 0;
      s = fresh_reader->GetBlob(read_options, user_key, offset, value_size,
                                compression_type, prefetch_buffer, allocator,
                                &blob_contents, &read_size);
      if (!s.ok()) {
        s = AppendBlobRefreshRetryFailure(stale_status, s);
      } else {
        CacheHandleGuard<BlobFileReader> ignored_reader;
        blob_file_cache_
            ->RefreshBlobFileReader(file_number, &fresh_reader, &ignored_reader)
            .PermitUncheckedError();
      }
    }
    if (!s.ok()) {
      return s;
    }
    if (bytes_read) {
      *bytes_read = read_size;
    }
  }

  if (blob_cache_ && read_options.fill_cache) {
    // If filling cache is allowed and a cache is configured, try to put the
    // blob to the cache.
    Slice key = cache_key.AsSlice();
    s = PutBlobIntoCache(key, &blob_contents, &blob_handle);
    if (!s.ok()) {
      return s;
    }

    PinCachedBlob(&blob_handle, value);
  } else {
    PinOwnedBlob(&blob_contents, value);
  }

  assert(s.ok());
  return s;
}

Status BlobSource::GetSimpleGen2Blob(
    const ReadOptions& read_options, const OffsetableCacheKey& base_cache_key,
    RandomAccessFileReader* file, uint64_t record_offset, uint64_t payload_size,
    ChecksumType checksum_type, uint32_t base_context_checksum,
    CompressionType expected_compression, PinnableSlice* value,
    uint64_t* bytes_read) {
  assert(value);
  assert(file);

  const uint64_t record_size = payload_size + kSimpleGen2BlobTrailerSize;

  // The cache key is derived from the SimpleGen2Blob format (shared scheme with
  // block-based SST blocks); see GetSimpleGen2BlobCacheKey.
  const CacheKey cache_key =
      GetSimpleGen2BlobCacheKey(base_cache_key, record_offset);

  Status s;

  CacheHandleGuard<BlobContents> blob_handle;

  // First, try to get the blob from the cache.
  if (blob_cache_) {
    Slice key = cache_key.AsSlice();
    s = GetBlobFromCache(key, &blob_handle);
    if (s.ok()) {
      PinCachedBlob(&blob_handle, value);

      // For consistency, the on-disk record size is assigned to bytes_read on
      // both cache hits and misses.
      if (bytes_read) {
        *bytes_read = record_size;
      }
      return s;
    }
  }

  assert(blob_handle.IsEmpty());

  const bool no_io = read_options.read_tier == kBlockCacheTier;
  if (no_io) {
    return Status::Incomplete("Cannot read blob(s): no disk I/O allowed");
  }

  // Cache miss (or no cache configured). Read the record into a buffer
  // allocated from the blob cache's memory allocator when we intend to insert
  // it, exposing the uncompressed payload as BlobContents (the trailer just
  // sits unused at the tail of the buffer).
  MemoryAllocator* const allocator = (blob_cache_ && read_options.fill_cache)
                                         ? blob_cache_.get()->memory_allocator()
                                         : nullptr;

  CacheAllocationPtr buf =
      AllocateBlock(static_cast<size_t>(record_size), allocator);
  s = ReadAndVerifySimpleGen2BlobRecord(
      read_options, file, record_offset, static_cast<size_t>(payload_size),
      static_cast<size_t>(record_size), checksum_type, base_context_checksum,
      expected_compression, buf.get());
  if (!s.ok()) {
    return s;
  }

  std::unique_ptr<BlobContents> blob_contents(
      new BlobContents(std::move(buf), static_cast<size_t>(payload_size)));

  // Record the per-read statistics (mirrors BlobFileReader::GetBlob).
  RecordTick(statistics_, BLOB_DB_BLOB_FILE_BYTES_READ, record_size);
  PERF_COUNTER_ADD(blob_read_count, 1);
  PERF_COUNTER_ADD(blob_read_byte, record_size);
  if (bytes_read) {
    *bytes_read = record_size;
  }

  if (blob_cache_ && read_options.fill_cache) {
    // If filling cache is allowed and a cache is configured, try to put the
    // blob into the cache.
    Slice key = cache_key.AsSlice();
    s = PutBlobIntoCache(key, &blob_contents, &blob_handle);
    if (!s.ok()) {
      return s;
    }

    PinCachedBlob(&blob_handle, value);
  } else {
    PinOwnedBlob(&blob_contents, value);
  }

  assert(s.ok());
  return s;
}

void BlobSource::MultiGetBlob(const ReadOptions& read_options,
                              autovector<BlobFileReadRequests>& blob_reqs,
                              uint64_t* bytes_read) {
  assert(blob_reqs.size() > 0);

  uint64_t total_bytes_read = 0;
  uint64_t bytes_read_in_file = 0;

  for (auto& [file_number, file_size, blob_reqs_in_file] : blob_reqs) {
    // sort blob_reqs_in_file by file offset.
    std::sort(
        blob_reqs_in_file.begin(), blob_reqs_in_file.end(),
        [](const BlobReadRequest& lhs, const BlobReadRequest& rhs) -> bool {
          return lhs.offset < rhs.offset;
        });

    MultiGetBlobFromOneFile(read_options, file_number, file_size,
                            blob_reqs_in_file, &bytes_read_in_file);

    total_bytes_read += bytes_read_in_file;
  }

  if (bytes_read) {
    *bytes_read = total_bytes_read;
  }
}

void BlobSource::MultiGetBlobFromOneFile(const ReadOptions& read_options,
                                         uint64_t file_number,
                                         uint64_t /*file_size*/,
                                         autovector<BlobReadRequest>& blob_reqs,
                                         uint64_t* bytes_read) {
  const size_t num_blobs = blob_reqs.size();
  assert(num_blobs > 0);
  assert(num_blobs <= MultiGetContext::MAX_BATCH_SIZE);

#ifndef NDEBUG
  for (size_t i = 0; i < num_blobs - 1; ++i) {
    assert(blob_reqs[i].offset <= blob_reqs[i + 1].offset);
  }
#endif  // !NDEBUG

  using Mask = uint64_t;
  Mask cache_hit_mask = 0;

  uint64_t total_bytes = 0;
  const OffsetableCacheKey base_cache_key(db_id_, db_session_id_, file_number);

  if (blob_cache_) {
    size_t cached_blob_count = 0;
    for (size_t i = 0; i < num_blobs; ++i) {
      auto& req = blob_reqs[i];

      CacheHandleGuard<BlobContents> blob_handle;
      const CacheKey cache_key = base_cache_key.WithOffset(req.offset);
      const Slice key = cache_key.AsSlice();

      const Status s = GetBlobFromCache(key, &blob_handle);

      if (s.ok()) {
        assert(req.status);
        *req.status = s;

        PinCachedBlob(&blob_handle, req.result);

        // Update the counter for the number of valid blobs read from the cache.
        ++cached_blob_count;

        // For consistency, the size of each on-disk (possibly compressed) blob
        // record is accumulated to total_bytes.
        uint64_t adjustment =
            read_options.verify_checksums
                ? BlobLogRecord::CalculateAdjustmentForRecordHeader(
                      req.user_key->size())
                : 0;
        assert(req.offset >= adjustment);
        total_bytes += req.len + adjustment;
        cache_hit_mask |= (Mask{1} << i);  // cache hit
      }
    }

    // All blobs were read from the cache.
    if (cached_blob_count == num_blobs) {
      if (bytes_read) {
        *bytes_read = total_bytes;
      }
      return;
    }
  }

  const bool no_io = read_options.read_tier == kBlockCacheTier;
  if (no_io) {
    for (size_t i = 0; i < num_blobs; ++i) {
      if (!(cache_hit_mask & (Mask{1} << i))) {
        BlobReadRequest& req = blob_reqs[i];
        assert(req.status);

        *req.status =
            Status::Incomplete("Cannot read blob(s): no disk I/O allowed");
      }
    }
    return;
  }

  {
    // Find the rest of blobs from the file since I/O is allowed.
    autovector<std::pair<BlobReadRequest*, std::unique_ptr<BlobContents>>>
        _blob_reqs;
    uint64_t _bytes_read = 0;

    for (size_t i = 0; i < num_blobs; ++i) {
      if (!(cache_hit_mask & (Mask{1} << i))) {
        _blob_reqs.emplace_back(&blob_reqs[i], std::unique_ptr<BlobContents>());
      }
    }

    CacheHandleGuard<BlobFileReader> blob_file_reader;
    Status s = blob_file_cache_->GetBlobFileReader(read_options, file_number,
                                                   &blob_file_reader);
    if (!s.ok()) {
      for (size_t i = 0; i < _blob_reqs.size(); ++i) {
        BlobReadRequest* const req = _blob_reqs[i].first;
        assert(req);
        assert(req->status);

        *req->status = s;
      }
      return;
    }

    assert(blob_file_reader.GetValue());

    MemoryAllocator* const allocator =
        (blob_cache_ && read_options.fill_cache)
            ? blob_cache_.get()->memory_allocator()
            : nullptr;

    blob_file_reader.GetValue()->MultiGetBlob(read_options, allocator,
                                              _blob_reqs, &_bytes_read);

    bool needs_reader_refresh = false;
    for (const auto& blob_req : _blob_reqs) {
      BlobReadRequest* const req = blob_req.first;
      assert(req != nullptr);
      assert(req->status != nullptr);
      if (req->status->IsCorruption()) {
        needs_reader_refresh = true;
        break;
      }
    }

    if (needs_reader_refresh) {
      blob_file_reader.Reset();
      blob_file_cache_->Evict(file_number);

      std::unique_ptr<BlobFileReader> fresh_reader;
      s = blob_file_cache_->OpenBlobFileReaderUncached(
          read_options, file_number, &fresh_reader,
          /*allow_footer_skip_retry=*/false);
      if (!s.ok()) {
        for (const auto& blob_req : _blob_reqs) {
          BlobReadRequest* const req = blob_req.first;
          assert(req != nullptr);
          assert(req->status != nullptr);
          if (req->status->IsCorruption()) {
            *req->status = AppendBlobRefreshRetryFailure(*req->status, s);
          }
        }
        return;
      }

      autovector<std::pair<BlobReadRequest*, std::unique_ptr<BlobContents>>>
          retry_blob_reqs;
      autovector<Status> stale_statuses;
      for (auto& blob_req : _blob_reqs) {
        BlobReadRequest* const req = blob_req.first;
        assert(req != nullptr);
        assert(req->status != nullptr);
        if (!req->status->IsCorruption()) {
          continue;
        }

        stale_statuses.emplace_back(*req->status);
        *req->status = Status::OK();
        blob_req.second.reset();
        retry_blob_reqs.emplace_back(req, std::unique_ptr<BlobContents>());
      }

      uint64_t refreshed_bytes_read = 0;
      fresh_reader->MultiGetBlob(read_options, allocator, retry_blob_reqs,
                                 &refreshed_bytes_read);
      _bytes_read += refreshed_bytes_read;

      bool install_fresh_reader = false;
      for (size_t i = 0; i < retry_blob_reqs.size(); ++i) {
        auto& retried_blob_req = retry_blob_reqs[i];
        BlobReadRequest* const retried_req = retried_blob_req.first;
        assert(retried_req != nullptr);
        if (retried_req->status->ok()) {
          install_fresh_reader = true;
        } else {
          *retried_req->status = AppendBlobRefreshRetryFailure(
              stale_statuses[i], *retried_req->status);
        }

        for (auto& blob_req : _blob_reqs) {
          if (blob_req.first != retried_req) {
            continue;
          }

          blob_req.second = std::move(retried_blob_req.second);
          break;
        }
      }

      if (install_fresh_reader) {
        CacheHandleGuard<BlobFileReader> ignored_reader;
        blob_file_cache_
            ->RefreshBlobFileReader(file_number, &fresh_reader, &ignored_reader)
            .PermitUncheckedError();
      }
    }

    if (blob_cache_ && read_options.fill_cache) {
      // If filling cache is allowed and a cache is configured, try to put
      // the blob(s) to the cache.
      for (auto& [req, blob_contents] : _blob_reqs) {
        assert(req);

        if (req->status->ok()) {
          CacheHandleGuard<BlobContents> blob_handle;
          const CacheKey cache_key = base_cache_key.WithOffset(req->offset);
          const Slice key = cache_key.AsSlice();
          s = PutBlobIntoCache(key, &blob_contents, &blob_handle);
          if (!s.ok()) {
            *req->status = s;
          } else {
            PinCachedBlob(&blob_handle, req->result);
          }
        }
      }
    } else {
      for (auto& [req, blob_contents] : _blob_reqs) {
        assert(req);

        if (req->status->ok()) {
          PinOwnedBlob(&blob_contents, req->result);
        }
      }
    }

    total_bytes += _bytes_read;
    if (bytes_read) {
      *bytes_read = total_bytes;
    }
  }
}

bool BlobSource::TEST_BlobInCache(uint64_t file_number, uint64_t file_size,
                                  uint64_t offset, size_t* charge) const {
  const CacheKey cache_key = GetCacheKey(file_number, file_size, offset);
  const Slice key = cache_key.AsSlice();

  CacheHandleGuard<BlobContents> blob_handle;
  const Status s = GetBlobFromCache(key, &blob_handle);

  if (s.ok() && blob_handle.GetValue() != nullptr) {
    if (charge) {
      const Cache* const cache = blob_handle.GetCache();
      assert(cache);

      Cache::Handle* const handle = blob_handle.GetCacheHandle();
      assert(handle);

      *charge = cache->GetUsage(handle);
    }

    return true;
  }

  return false;
}

}  // namespace ROCKSDB_NAMESPACE