//  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.

//  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).

//

// Copyright (c) 2011 The LevelDB Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include "db/table_cache.h"

#include <algorithm>

#include "db/dbformat.h"

#include "db/range_tombstone_fragmenter.h"

#include "db/snapshot_impl.h"

#include "db/version_edit.h"

#include "file/file_util.h"

#include "file/filename.h"

#include "file/random_access_file_reader.h"

#include "logging/logging.h"

#include "monitoring/file_read_sample.h"

#include "monitoring/perf_context_imp.h"

#include "options/options_helper.h"

#include "rocksdb/advanced_options.h"

#include "rocksdb/statistics.h"

#include "table/block_based/block_based_table_reader.h"

#include "table/get_context.h"

#include "table/internal_iterator.h"

#include "table/iterator_wrapper.h"

#include "table/multiget_context.h"

#include "table/table_builder.h"

#include "table/table_reader.h"

#include "test_util/sync_point.h"

#include "util/cast_util.h"

#include "util/coding.h"

#include "util/stop_watch.h"

// Generate the regular and coroutine versions of some methods by

// including table_cache_sync_and_async.h twice

// Macros in the header will expand differently based on whether

// WITH_COROUTINES or WITHOUT_COROUTINES is defined

// clang-format off

#define WITHOUT_COROUTINES

#include "db/table_cache_sync_and_async.h"

#undef WITHOUT_COROUTINES

#define WITH_COROUTINES

#include "db/table_cache_sync_and_async.h"

#undef WITH_COROUTINES

// clang-format on

namespace ROCKSDB_NAMESPACE {

namespace {

static Slice GetSliceForFileNumber(const uint64_t* file_number) {

  return Slice(reinterpret_cast<const char*>(file_number),

               sizeof(*file_number));

}

void AppendVarint64(IterKey* key, uint64_t v) {

  char buf[10];

  auto ptr = EncodeVarint64(buf, v);

  key->TrimAppend(key->Size(), buf, ptr - buf);

}

}  // anonymous namespace

const int kLoadConcurency = 128;

TableCache::TableCache(const ImmutableOptions& ioptions,

                       const FileOptions* file_options, Cache* const cache,

                       BlockCacheTracer* const block_cache_tracer,

                       const std::shared_ptr<IOTracer>& io_tracer,

                       const std::string& db_session_id, bool fast_sst_open)

    : ioptions_(ioptions),

      file_options_(*file_options),

      cache_(cache),

      immortal_tables_(false),

      should_pin_table_handles_(cache_.get()->GetCapacity() >=

                                kInfiniteCapacity),

      fast_sst_open_(fast_sst_open),

      block_cache_tracer_(block_cache_tracer),

      loader_mutex_(kLoadConcurency),

      io_tracer_(io_tracer),

      db_session_id_(db_session_id) {

  if (ioptions_.row_cache) {

    // If the same cache is shared by multiple instances, we need to

    // disambiguate its entries.

    PutVarint64(&row_cache_id_, ioptions_.row_cache->NewId());

  }

}

TableCache::~TableCache() = default;

Status TableCache::GetTableReader(

    const ReadOptions& ro, const FileOptions& file_options,

    const InternalKeyComparator& internal_comparator,

    const FileMetaData& file_meta, bool sequential_mode,

    HistogramImpl* file_read_hist, std::unique_ptr<TableReader>* table_reader,

    const MutableCFOptions& mutable_cf_options, bool skip_filters, int level,

    bool prefetch_index_and_filter_in_cache,

    size_t max_file_size_for_l0_meta_pin, Temperature file_temperature,

    std::string* file_open_metadata, bool avoid_shared_metadata_cache) {

  std::string fname = TableFileName(

      ioptions_.cf_paths, file_meta.fd.GetNumber(), file_meta.fd.GetPathId());

  std::unique_ptr<FSRandomAccessFile> file;

  FileOptions fopts = file_options;

  fopts.temperature = file_temperature;

  fopts.file_checksum = file_meta.file_checksum;

  fopts.file_checksum_func_name = file_meta.file_checksum_func_name;

  // Pass file open metadata for fast SST open. Use a local copy since

  // fopts.file_metadata is a non-owning pointer and file_meta is const.

  // Only pass metadata when fast_sst_open is enabled; otherwise ignore

  // previously persisted metadata (e.g. stale filesystem credentials).

  std::string file_open_metadata_copy;

  if (fast_sst_open_.load(std::memory_order_relaxed) &&

      !file_meta.file_open_metadata.empty()) {

    file_open_metadata_copy = file_meta.file_open_metadata;

    fopts.file_metadata = &file_open_metadata_copy;

    RecordTick(ioptions_.stats, FILE_OPEN_METADATA_PASSED);

  }

  Status s = PrepareIOFromReadOptions(ro, ioptions_.clock, fopts.io_options);

  TEST_SYNC_POINT_CALLBACK("TableCache::GetTableReader:BeforeOpenFile",

                           const_cast<Status*>(&s));

  if (s.ok()) {

    s = ioptions_.fs->NewRandomAccessFile(fname, fopts, &file, nullptr);

  }

  if (s.ok()) {

    RecordTick(ioptions_.stats, NO_FILE_OPENS);

  } else if (s.IsPathNotFound()) {

    fname = Rocks2LevelTableFileName(fname);

    // If this file is also not found, we want to use the error message

    // that contains the table file name which is less confusing.

    Status temp_s =

        PrepareIOFromReadOptions(ro, ioptions_.clock, fopts.io_options);

    if (temp_s.ok()) {

      temp_s = ioptions_.fs->NewRandomAccessFile(fname, fopts, &file, nullptr);

    }

    if (temp_s.ok()) {

      RecordTick(ioptions_.stats, NO_FILE_OPENS);

      s = temp_s;

    }

  }

  if (s.ok()) {

    // Retrieve file open metadata before wrapping the file

    if (file_open_metadata != nullptr) {

      IOStatus io_s = file->GetFileOpenMetadata(file_open_metadata);

      if (io_s.ok() && !file_open_metadata->empty() &&

          file_open_metadata->size() <=

              FSRandomAccessFile::kMaxFileOpenMetadataSize) {

        RecordTick(ioptions_.stats, FILE_OPEN_METADATA_RETRIEVED);

      } else {

        if (io_s.ok() && file_open_metadata->size() >

                             FSRandomAccessFile::kMaxFileOpenMetadataSize) {

          ROCKS_LOG_WARN(ioptions_.logger,

                         "File open metadata for %s too large (%zu bytes), "

                         "ignoring",

                         fname.c_str(), file_open_metadata->size());

        }

        file_open_metadata->clear();

      }

    }

    if (!sequential_mode && ioptions_.advise_random_on_open) {

      file->Hint(FSRandomAccessFile::kRandom);

    }

    if (ioptions_.default_temperature != Temperature::kUnknown &&

        file_temperature == Temperature::kUnknown) {

      file_temperature = ioptions_.default_temperature;

    }

    StopWatch sw(ioptions_.clock, ioptions_.stats, TABLE_OPEN_IO_MICROS);

    std::unique_ptr<RandomAccessFileReader> file_reader(

        new RandomAccessFileReader(std::move(file), fname, ioptions_.clock,

                                   io_tracer_, ioptions_.stats, SST_READ_MICROS,

                                   file_read_hist, ioptions_.rate_limiter.get(),

                                   ioptions_.listeners, file_temperature,

                                   level == ioptions_.num_levels - 1));

    UniqueId64x2 expected_unique_id;

    if (ioptions_.verify_sst_unique_id_in_manifest) {

      expected_unique_id = file_meta.unique_id;

    } else {

      expected_unique_id = kNullUniqueId64x2;  // null ID == no verification

    }

    TableReaderOptions table_reader_options(

        ioptions_, mutable_cf_options.prefix_extractor,

        mutable_cf_options.compression_manager.get(), file_options,

        internal_comparator, mutable_cf_options.block_protection_bytes_per_key,

        skip_filters, immortal_tables_, false /* force_direct_prefetch */,

        level, block_cache_tracer_, max_file_size_for_l0_meta_pin,

        db_session_id_, file_meta.fd.GetNumber(), expected_unique_id,

        file_meta.fd.largest_seqno, file_meta.tail_size,

        file_meta.user_defined_timestamps_persisted,

        avoid_shared_metadata_cache);

    // Route same-file ("embedded") blob reads through the CFD's BlobSource for

    // caching + stats. nullptr in non-DB contexts (e.g. repair).

    table_reader_options.blob_source = blob_source_;

    s = mutable_cf_options.table_factory->NewTableReader(

        ro, table_reader_options, std::move(file_reader),

        file_meta.fd.GetFileSize(), table_reader,

        prefetch_index_and_filter_in_cache);

    TEST_SYNC_POINT("TableCache::GetTableReader:0");

  }

  return s;

}

Cache::Handle* TableCache::Lookup(Cache* cache, uint64_t file_number) {

  // NOTE: sharing same Cache with BlobFileCache

  Slice key = GetSliceForFileNumber(&file_number);

  return cache->Lookup(key);

}

// TODO: consider making handle RAII.

Status TableCache::FindTable(

    const ReadOptions& ro, const FileOptions& file_options,

    const InternalKeyComparator& internal_comparator,

    const FileMetaData& file_meta, TypedHandle** handle,

    const MutableCFOptions& mutable_cf_options, TableReader** out_table_reader,

    const bool no_io, HistogramImpl* file_read_hist, bool skip_filters,

    int level, bool prefetch_index_and_filter_in_cache,

    size_t max_file_size_for_l0_meta_pin, Temperature file_temperature,

    bool pin_table_handle, std::string* file_open_metadata,

    std::unique_ptr<TableReader>* fresh_table_reader_owner,

    const TableCacheOpenOptions& open_options) {

  assert(out_table_reader != nullptr && *out_table_reader == nullptr);

  assert(handle != nullptr && *handle == nullptr);

  // open_ephemeral_table_reader requests a fresh reader;

  // fresh_table_reader_owner is where we return it. The two must agree.

  assert(open_options.open_ephemeral_table_reader ==

         (fresh_table_reader_owner != nullptr));

  PERF_TIMER_GUARD_WITH_CLOCK(find_table_nanos, ioptions_.clock);

  // Bypass path: open a fresh TableReader, skipping the pinned-reader fast path

  // and the shared cache. The caller takes ownership via

  // fresh_table_reader_owner. no_io is not allowed here since opening a new

  // reader always needs I/O.

  if (fresh_table_reader_owner != nullptr) {

    assert(!no_io);

    if (no_io) {

      // Defensive in release builds: the caller violated the contract.

      return Status::Incomplete(

          "fresh TableReader requested but no_io is set; cannot open file");

    }

    std::unique_ptr<TableReader> table_reader;

    const bool effective_skip_filters =

        skip_filters || open_options.skip_filters;

    TEST_SYNC_POINT_CALLBACK("TableCache::FindTable:FreshTableReader",

                             const_cast<TableCacheOpenOptions*>(&open_options));

    Status s = GetTableReader(

        ro, file_options, internal_comparator, file_meta,

        false /* sequential mode */, file_read_hist, &table_reader,

        mutable_cf_options, effective_skip_filters, level,

        prefetch_index_and_filter_in_cache &&

            !open_options.avoid_shared_metadata_cache,

        max_file_size_for_l0_meta_pin, file_temperature, file_open_metadata,

        open_options.avoid_shared_metadata_cache);

    if (!s.ok()) {

      assert(table_reader == nullptr);

      RecordTick(ioptions_.stats, NO_FILE_ERRORS);

      IGNORE_STATUS_IF_ERROR(s);

      return s;

    }

    *out_table_reader = table_reader.get();

    *fresh_table_reader_owner = std::move(table_reader);

    *handle = nullptr;

    return s;

  }

  // Fast path: if table reader is already pinned, return it directly without a

  // cache lookup.

  auto pinned_reader = file_meta.fd.pinned_reader.Get();

  if (pinned_reader != nullptr) {

    *handle = nullptr;

    *out_table_reader = pinned_reader;

    return Status::OK();

  }

  uint64_t number = file_meta.fd.GetNumber();

  // NOTE: sharing same Cache with BlobFileCache

  Slice key = GetSliceForFileNumber(&number);

  *handle = cache_.Lookup(key);

  TEST_SYNC_POINT_CALLBACK("TableCache::FindTable:0",

                           const_cast<bool*>(&no_io));

  Status s = Status::OK();

  if (*handle == nullptr) {

    if (no_io) {

      s = Status::Incomplete("Table not found in table_cache, no_io is set");

      return s;

    }

    MutexLock load_lock(&loader_mutex_.Get(key));

    // Check if another thread has already pinned the table reader

    pinned_reader = file_meta.fd.pinned_reader.Get();

    if (pinned_reader != nullptr) {

      *handle = nullptr;

      *out_table_reader = pinned_reader;

      return s;

    }

    // We check the cache again under loading mutex

    *handle = cache_.Lookup(key);

    if (*handle == nullptr) {

      std::unique_ptr<TableReader> table_reader;

      s = GetTableReader(ro, file_options, internal_comparator, file_meta,

                         false /* sequential mode */, file_read_hist,

                         &table_reader, mutable_cf_options, skip_filters, level,

                         prefetch_index_and_filter_in_cache,

                         max_file_size_for_l0_meta_pin, file_temperature,

                         file_open_metadata);

      if (!s.ok()) {

        assert(table_reader == nullptr);

        RecordTick(ioptions_.stats, NO_FILE_ERRORS);

        // We do not cache error results so that if the error is transient,

        // or somebody repairs the file, we recover automatically.

        IGNORE_STATUS_IF_ERROR(s);

      } else {

        s = cache_.Insert(key, table_reader.get(), 1, handle);

        if (s.ok()) {

          // Release ownership of table reader.

          (void)table_reader.release();

        }

      }

    }

    if (s.ok()) {

      *out_table_reader = cache_.Value(*handle);

      if (pin_table_handle) {

        file_meta.fd.pinned_reader.Pin(*handle, *out_table_reader);

        *handle = nullptr;

      }

    }

  } else {

    *out_table_reader = cache_.Value(*handle);

    if (pin_table_handle) {

      // handle is in cache but not pinned. This should happen fairly rarely,

      // and once the reader is pinned, we will no longer need to go through

      // these mutexes again.

      MutexLock load_lock(&loader_mutex_.Get(key));

      if (file_meta.fd.pinned_reader.Get() != nullptr) {

        // Another thread has pinned the handle; release our lookup ref.

        cache_.Release(*handle);

      } else {

        file_meta.fd.pinned_reader.Pin(*handle, *out_table_reader);

      }

      *handle = nullptr;

    }

  }

  return s;

}

InternalIterator* TableCache::NewIterator(

    const ReadOptions& options, const FileOptions& file_options,

    const InternalKeyComparator& icomparator, const FileMetaData& file_meta,

    RangeDelAggregator* range_del_agg,

    const MutableCFOptions& mutable_cf_options, TableReader** table_reader_ptr,

    HistogramImpl* file_read_hist, TableReaderCaller caller, Arena* arena,

    bool skip_filters, int level, size_t max_file_size_for_l0_meta_pin,

    const InternalKey* smallest_compaction_key,

    const InternalKey* largest_compaction_key, bool allow_unprepared_value,

    const SequenceNumber* read_seqno,

    std::unique_ptr<TruncatedRangeDelIterator>* range_del_iter,

    bool maybe_pin_table_handle, std::string* file_open_metadata,

    const TableCacheOpenOptions& open_options) {

  PERF_TIMER_GUARD(new_table_iterator_nanos);

  Status s;

  TableReader* table_reader = nullptr;

  TypedHandle* handle = nullptr;

  assert(!open_options.open_ephemeral_table_reader ||

         table_reader_ptr == nullptr);

  // Holds ownership of a freshly-opened TableReader when the caller asked us

  // to bypass the shared cache. When non-empty, the iterator we hand back must

  // arrange to free it on destruction.

  std::unique_ptr<TableReader> ephemeral_reader;

  if (table_reader_ptr != nullptr) {

    *table_reader_ptr = nullptr;

  }

  const bool effective_skip_filters = skip_filters || open_options.skip_filters;

  bool for_compaction = caller == TableReaderCaller::kCompaction;

  TEST_SYNC_POINT_CALLBACK("TableCache::NewIterator::BeforeFindTable",

                           const_cast<FileDescriptor*>(&file_meta.fd));

  s = FindTable(

      options, file_options, icomparator, file_meta, &handle,

      mutable_cf_options, &table_reader,

      options.read_tier == kBlockCacheTier /* no_io */, file_read_hist,

      effective_skip_filters, level,

      /*prefetch_index_and_filter_in_cache=*/

      !open_options.avoid_shared_metadata_cache, max_file_size_for_l0_meta_pin,

      file_meta.temperature,

      maybe_pin_table_handle && should_pin_table_handles_, file_open_metadata,

      open_options.open_ephemeral_table_reader ? &ephemeral_reader : nullptr,

      open_options);

  InternalIterator* result = nullptr;

  if (s.ok()) {

    if (HasTableFilter(options) &&

        !(*options.table_filter)(*table_reader->GetTableProperties())) {

      result = NewEmptyInternalIterator<Slice>(arena);

    } else {

      result = table_reader->NewIterator(

          options, mutable_cf_options.prefix_extractor.get(), arena,

          effective_skip_filters, caller,

          file_options.compaction_readahead_size, allow_unprepared_value);

    }

    if (handle != nullptr) {

      cache_.RegisterReleaseAsCleanup(handle, *result);

      handle = nullptr;  // prevent from releasing below

    }

    // Don't hand ephemeral_reader to result's cleanup yet: range-del

    // processing below can set s to non-OK, in which case result is replaced

    // by an error iterator at function end. Transfer ownership only once we

    // know s stays OK; otherwise ephemeral_reader's destructor frees it.

    if (for_compaction) {

      table_reader->SetupForCompaction();

    }

    if (table_reader_ptr != nullptr) {

      *table_reader_ptr = table_reader;

    }

  }

  if (s.ok() && !options.ignore_range_deletions) {

    if (range_del_iter != nullptr) {

      auto new_range_del_iter =

          read_seqno ? table_reader->NewRangeTombstoneIterator(

                           *read_seqno, options.timestamp)

                     : table_reader->NewRangeTombstoneIterator(options);

      if (new_range_del_iter == nullptr || new_range_del_iter->empty()) {

        delete new_range_del_iter;

        *range_del_iter = nullptr;

      } else {

        *range_del_iter = std::make_unique<TruncatedRangeDelIterator>(

            std::unique_ptr<FragmentedRangeTombstoneIterator>(

                new_range_del_iter),

            &icomparator, &file_meta.smallest, &file_meta.largest);

      }

    }

    if (range_del_agg != nullptr) {

      if (range_del_agg->AddFile(file_meta.fd.GetNumber())) {

        std::unique_ptr<FragmentedRangeTombstoneIterator> new_range_del_iter(

            static_cast<FragmentedRangeTombstoneIterator*>(

                table_reader->NewRangeTombstoneIterator(options)));

        if (new_range_del_iter != nullptr) {

          s = new_range_del_iter->status();

        }

        if (s.ok()) {

          const InternalKey* smallest = &file_meta.smallest;

          const InternalKey* largest = &file_meta.largest;

          if (smallest_compaction_key != nullptr) {

            smallest = smallest_compaction_key;

          }

          if (largest_compaction_key != nullptr) {

            largest = largest_compaction_key;

          }

          range_del_agg->AddTombstones(std::move(new_range_del_iter), smallest,

                                       largest);

        }

      }

    }

  }

  if (handle != nullptr) {

    cache_.Release(handle);

  }

  // Range-del processing is done and s is final. Hand the ephemeral reader's

  // lifetime to the returned iterator; if s is non-OK, leave it for

  // ephemeral_reader's destructor. RegisterCleanup gets the raw pointer before

  // release(), so if its allocation throws the reader is still owned by

  // ephemeral_reader and freed on unwind.

  if (s.ok() && ephemeral_reader && result != nullptr) {

    TableReader* raw = ephemeral_reader.get();

    result->RegisterCleanup(

        [](void* arg1, void* /*arg2*/) {

          delete static_cast<TableReader*>(arg1);

        },

        raw, nullptr);

    // release() returns raw, which the cleanup now owns; drop the unique_ptr's

    // ownership so the reader isn't freed twice.

    [[maybe_unused]] TableReader* released = ephemeral_reader.release();

    assert(released == raw);

  }

  if (!s.ok()) {

    // Today result is always null here: it is only set when s was OK, and the

    // only later change to s, new_range_del_iter->status(), is always OK for a

    // FragmentedRangeTombstoneIterator. The assert documents that; the cleanup

    // still disposes of any stray result before the error iterator replaces it.

    assert(result == nullptr);

    if (result != nullptr) {

      if (arena != nullptr) {

        result->~InternalIterator();

      } else {

        delete result;

      }

      result = nullptr;

    }

    result = NewErrorInternalIterator<Slice>(s, arena);

  }

  return result;

}

Status TableCache::GetRangeTombstoneIterator(

    const ReadOptions& options,

    const InternalKeyComparator& internal_comparator,

    const FileMetaData& file_meta, const MutableCFOptions& mutable_cf_options,

    std::unique_ptr<FragmentedRangeTombstoneIterator>* out_iter) {

  assert(out_iter);

  Status s;

  TableReader* t = nullptr;

  TypedHandle* handle = nullptr;

  s = FindTable(options, file_options_, internal_comparator, file_meta, &handle,

                mutable_cf_options, &t);

  if (s.ok()) {

    // Note: NewRangeTombstoneIterator could return nullptr

    out_iter->reset(t->NewRangeTombstoneIterator(options));

  }

  if (handle) {

    if (*out_iter) {

      cache_.RegisterReleaseAsCleanup(handle, **out_iter);

    } else {

      cache_.Release(handle);

    }

  }

  return s;

}

uint64_t TableCache::CreateRowCacheKeyPrefix(const ReadOptions& options,

                                             const FileDescriptor& fd,

                                             const Slice& internal_key,

                                             GetContext* get_context,

                                             IterKey& row_cache_key) {

  uint64_t fd_number = fd.GetNumber();

  // We use the user key as cache key instead of the internal key,

  // otherwise the whole cache would be invalidated every time the

  // sequence key increases. However, to support caching snapshot

  // reads, we append a sequence number (incremented by 1 to

  // distinguish from 0) other than internal_key seq no

  // to determine row cache entry visibility.

  // If the snapshot is larger than the largest seqno in the file,

  // all data should be exposed to the snapshot, so we treat it

  // the same as there is no snapshot. The exception is that if

  // a seq-checking callback is registered, some internal keys

  // may still be filtered out.

  uint64_t cache_entry_seq_no = 0;

  // Maybe we can include the whole file ifsnapshot == fd.largest_seqno.

  if (options.snapshot != nullptr &&

      (get_context->has_callback() ||

       static_cast_with_check<const SnapshotImpl>(options.snapshot)

               ->GetSequenceNumber() <= fd.largest_seqno)) {

    // We should consider to use options.snapshot->GetSequenceNumber()

    // instead of GetInternalKeySeqno(k), which will make the code

    // easier to understand.

    const MetadataReadBounds* metadata_read_bounds =

        get_context->metadata_read_bounds();

    cache_entry_seq_no = 1 + (metadata_read_bounds != nullptr

                                  ? metadata_read_bounds->read_snapshot_seq

                                  : GetInternalKeySeqno(internal_key));

  }

  // Compute row cache key.

  row_cache_key.TrimAppend(row_cache_key.Size(), row_cache_id_.data(),

                           row_cache_id_.size());

  AppendVarint64(&row_cache_key, fd_number);

  AppendVarint64(&row_cache_key, cache_entry_seq_no);

  // Provide a sequence number for callback checking on cache hit.

  // As cache_entry_seq_no starts at 1, decrease it's value by 1 to get

  // a sequence number align with get context's logic.

  return cache_entry_seq_no == 0 ? 0 : cache_entry_seq_no - 1;

}

bool TableCache::GetFromRowCache(const Slice& user_key, IterKey& row_cache_key,

                                 size_t prefix_size, GetContext* get_context,

                                 Status* read_status, SequenceNumber seq_no) {

  bool found = false;

  row_cache_key.TrimAppend(prefix_size, user_key.data(), user_key.size());

  RowCacheInterface row_cache{ioptions_.row_cache.get()};

  if (auto row_handle = row_cache.Lookup(row_cache_key.GetUserKey())) {

    // Cleanable routine to release the cache entry

    Cleanable value_pinner;

    // If it comes here value is located on the cache.

    // found_row_cache_entry points to the value on cache,

    // and value_pinner has cleanup procedure for the cached entry.

    // After replayGetContextLog() returns, get_context.pinnable_slice_

    // will point to cache entry buffer (or a copy based on that) and

    // cleanup routine under value_pinner will be delegated to

    // get_context.pinnable_slice_. Cache entry is released when

    // get_context.pinnable_slice_ is reset.

    row_cache.RegisterReleaseAsCleanup(row_handle, value_pinner);

    // If row cache hit, knowing cache key is the same to row_cache_key,

    // can use row_cache_key's seq no to construct InternalKey.

    *read_status = replayGetContextLog(*row_cache.Value(row_handle), user_key,

                                       get_context, &value_pinner, seq_no);

    RecordTick(ioptions_.stats, ROW_CACHE_HIT);

    found = true;

  } else {

    RecordTick(ioptions_.stats, ROW_CACHE_MISS);

  }

  return found;

}

void TableCache::UpdateRangeTombstoneSeqnums(

    const ReadOptions& options, TableReader* t,

    MultiGetContext::Range& table_range) {

  std::unique_ptr<FragmentedRangeTombstoneIterator> latest_range_del_iter;

  bool track_newer_versions = false;

  if (!table_range.empty()) {

    ReadCallback* callback = table_range.begin()->get_context->read_callback();

    if (callback != nullptr && callback->GetMetadataReadBounds() != nullptr) {

      for (auto iter = table_range.begin(); iter != table_range.end(); ++iter) {

        if (iter->get_context->NeedToTrackNewerVersions()) {

          track_newer_versions = true;

          break;

        }

      }

    }

  }

  if (track_newer_versions) {

    SequenceNumber latest_range_del_read_seq = 0;

    for (auto iter = table_range.begin(); iter != table_range.end(); ++iter) {

      if (iter->get_context->NeedToTrackNewerVersions()) {

        latest_range_del_read_seq = std::max(latest_range_del_read_seq,

                                             GetInternalKeySeqno(iter->ikey));

      }

    }

    if (latest_range_del_read_seq > 0) {

      latest_range_del_iter.reset(t->NewRangeTombstoneIterator(

          latest_range_del_read_seq, options.timestamp));

    }

  }

  std::unique_ptr<FragmentedRangeTombstoneIterator> range_del_iter;

  if (!options.ignore_range_deletions) {

    range_del_iter.reset(t->NewRangeTombstoneIterator(options));

  }

  if (range_del_iter != nullptr || latest_range_del_iter != nullptr) {

    for (auto iter = table_range.begin(); iter != table_range.end(); ++iter) {

      if (latest_range_del_iter != nullptr &&

          iter->get_context->NeedToTrackNewerVersions()) {

        const SequenceNumber covering_seq =

            latest_range_del_iter->MaxCoveringTombstoneSeqnum(

                iter->ukey_with_ts, iter->get_context->read_callback());

        if (covering_seq != 0) {

          iter->get_context->RecordNewerVersionIfNeeded(covering_seq,

                                                        kTypeRangeDeletion);

        }

      }

      if (range_del_iter == nullptr) {

        continue;

      }

      SequenceNumber* max_covering_tombstone_seq =

          iter->get_context->max_covering_tombstone_seq();

      SequenceNumber seq =

          range_del_iter->MaxCoveringTombstoneSeqnum(iter->ukey_with_ts);

      if (seq > *max_covering_tombstone_seq) {

        *max_covering_tombstone_seq = seq;

        if (iter->get_context->NeedTimestamp()) {

          iter->get_context->SetTimestampFromRangeTombstone(

              range_del_iter->timestamp());

        }

      }

    }

  }

}

Status TableCache::MultiGetFilter(

    const ReadOptions& options,

    const InternalKeyComparator& internal_comparator,

    const FileMetaData& file_meta, const MutableCFOptions& mutable_cf_options,

    HistogramImpl* file_read_hist, int level,

    MultiGetContext::Range* mget_range, TypedHandle** handle) {

  assert(*handle == nullptr);

  IterKey row_cache_key;

  std::string row_cache_entry_buffer;

  // Check if we need to use the row cache. If yes, then we cannot do the

  // filtering here, since the filtering needs to happen after the row cache

  // lookup.

  KeyContext& first_key = *mget_range->begin();

  bool track_newer_versions = false;

  ReadCallback* callback = first_key.get_context->read_callback();

  if (callback != nullptr && callback->GetMetadataReadBounds() != nullptr) {

    for (auto iter = mget_range->begin(); iter != mget_range->end(); ++iter) {

      if (iter->get_context->NeedToTrackNewerVersions()) {

        track_newer_versions = true;

        break;

      }

    }

  }

  if (ioptions_.row_cache && !first_key.get_context->NeedToReadSequence() &&

      !track_newer_versions) {

    return Status::NotSupported();

  }

  Status s;

  TableReader* t = nullptr;

  MultiGetContext::Range tombstone_range(*mget_range, mget_range->begin(),

                                         mget_range->end());

  s = FindTable(options, file_options_, internal_comparator, file_meta, handle,

                mutable_cf_options, &t,

                options.read_tier == kBlockCacheTier /* no_io */,

                file_read_hist,

                /*skip_filters=*/false, level,

                true /* prefetch_index_and_filter_in_cache */,

                /*max_file_size_for_l0_meta_pin=*/0, file_meta.temperature,

                should_pin_table_handles_);

  if (s.ok()) {

    s = t->MultiGetFilter(options, mutable_cf_options.prefix_extractor.get(),

                          mget_range);

  }

  if (s.ok() && (!options.ignore_range_deletions || track_newer_versions)) {

    // Update the range tombstone sequence numbers for the keys here

    // as TableCache::MultiGet may or may not be called, and even if it

    // is, it may be called with fewer keys in the rangedue to filtering.

    UpdateRangeTombstoneSeqnums(options, t, tombstone_range);

  }

  if (mget_range->empty() && *handle) {

    cache_.Release(*handle);

    *handle = nullptr;

  }

  return s;

}

Status TableCache::GetTableProperties(

    const FileOptions& file_options, const ReadOptions& read_options,

    const InternalKeyComparator& internal_comparator,

    const FileMetaData& file_meta,

    std::shared_ptr<const TableProperties>* properties,

    const MutableCFOptions& mutable_cf_options, bool no_io) {

  TypedHandle* table_handle = nullptr;

  TableReader* table = nullptr;

  Status s =

      FindTable(read_options, file_options, internal_comparator, file_meta,

                &table_handle, mutable_cf_options, &table, no_io);

  if (!s.ok()) {

    return s;

  }

  *properties = table->GetTableProperties();

  if (table_handle) {

    cache_.Release(table_handle);

  }

  return s;

}

Status TableCache::ApproximateKeyAnchors(

    const ReadOptions& ro, const InternalKeyComparator& internal_comparator,

    const FileMetaData& file_meta, const MutableCFOptions& mutable_cf_options,

    std::vector<TableReader::Anchor>& anchors) {

  Status s;

  TableReader* t = nullptr;

  TypedHandle* handle = nullptr;

  s = FindTable(ro, file_options_, internal_comparator, file_meta, &handle,

                mutable_cf_options, &t);

  if (s.ok() && t != nullptr) {

    s = t->ApproximateKeyAnchors(ro, anchors);

  }

  if (handle != nullptr) {

    cache_.Release(handle);

  }

  return s;

}

size_t TableCache::GetMemoryUsageByTableReader(

    const FileOptions& file_options, const ReadOptions& read_options,

    const InternalKeyComparator& internal_comparator,

    const FileMetaData& file_meta, const MutableCFOptions& mutable_cf_options) {

  TypedHandle* table_handle = nullptr;

  TableReader* table = nullptr;

  Status s =

      FindTable(read_options, file_options, internal_comparator, file_meta,

                &table_handle, mutable_cf_options, &table, true /* no_io */);

  if (!s.ok()) {

    return 0;

  }

  auto ret = table->ApproximateMemoryUsage();

  if (table_handle) {

    cache_.Release(table_handle);

  }

  return ret;

}

void TableCache::Evict(Cache* cache, uint64_t file_number) {

  cache->Erase(GetSliceForFileNumber(&file_number));

}

uint64_t TableCache::ApproximateOffsetOf(

    const ReadOptions& read_options, const Slice& key,

    const FileMetaData& file_meta, TableReaderCaller caller,

    const InternalKeyComparator& internal_comparator,

    const MutableCFOptions& mutable_cf_options) {

  uint64_t result = 0;

  TableReader* table_reader = nullptr;

  TypedHandle* table_handle = nullptr;

  Status s =

      FindTable(read_options, file_options_, internal_comparator, file_meta,

                &table_handle, mutable_cf_options, &table_reader);

  if (s.ok() && table_reader != nullptr) {

    result = table_reader->ApproximateOffsetOf(read_options, key, caller);

  }

  if (table_handle != nullptr) {

    cache_.Release(table_handle);

  }

  return result;

}

uint64_t TableCache::ApproximateSize(

    const ReadOptions& read_options, const Slice& start, const Slice& end,

    const FileMetaData& file_meta, TableReaderCaller caller,

    const InternalKeyComparator& internal_comparator,

    const MutableCFOptions& mutable_cf_options) {

  uint64_t result = 0;

  TableReader* table_reader = nullptr;

  TypedHandle* table_handle = nullptr;

  Status s =

      FindTable(read_options, file_options_, internal_comparator, file_meta,

                &table_handle, mutable_cf_options, &table_reader);

  if (s.ok() && table_reader != nullptr) {

    result = table_reader->ApproximateSize(read_options, start, end, caller);

  }

  if (table_handle != nullptr) {

    cache_.Release(table_handle);

  }

  return result;

}

void TableCache::ReleaseObsolete(Cache* cache, uint64_t file_number,

                                 Cache::Handle* h,

                                 uint32_t uncache_aggressiveness) {

  CacheInterface typed_cache(cache);

  TypedHandle* table_handle = reinterpret_cast<TypedHandle*>(h);

  if (table_handle == nullptr) {

    table_handle = typed_cache.Lookup(GetSliceForFileNumber(&file_number));

  }

  if (table_handle != nullptr) {

    TableReader* table_reader = typed_cache.Value(table_handle);

    table_reader->MarkObsolete(uncache_aggressiveness);

    // Mark the entry Invisible so that if concurrent readers hold references,

    // the entry will be erased when the last reference is released.

    cache->Erase(GetSliceForFileNumber(&file_number));

    typed_cache.Release(table_handle);

  }

}

}  // namespace ROCKSDB_NAMESPACE