rocksdb/file/random_access_file_reader.cc

//  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 "file/random_access_file_reader.h"

#include <algorithm>
#include <mutex>

#include "monitoring/histogram.h"
#include "monitoring/iostats_context_imp.h"
#include "port/port.h"
#include "test_util/sync_point.h"
#include "util/random.h"
#include "util/rate_limiter.h"

namespace rocksdb {
Status RandomAccessFileReader::Read(uint64_t offset, size_t n, Slice* result,
                                    char* scratch, bool for_compaction) const {
  Status s;
  uint64_t elapsed = 0;
  {
    StopWatch sw(env_, stats_, hist_type_,
                 (stats_ != nullptr) ? &elapsed : nullptr, true /*overwrite*/,
                 true /*delay_enabled*/);
    auto prev_perf_level = GetPerfLevel();
    IOSTATS_TIMER_GUARD(read_nanos);
    if (use_direct_io()) {
#ifndef ROCKSDB_LITE
      size_t alignment = file_->GetRequiredBufferAlignment();
      size_t aligned_offset =
          TruncateToPageBoundary(alignment, static_cast<size_t>(offset));
      size_t offset_advance = static_cast<size_t>(offset) - aligned_offset;
      size_t read_size =
          Roundup(static_cast<size_t>(offset + n), alignment) - aligned_offset;
      AlignedBuffer buf;
      buf.Alignment(alignment);
      buf.AllocateNewBuffer(read_size);
      while (buf.CurrentSize() < read_size) {
        size_t allowed;
        if (for_compaction && rate_limiter_ != nullptr) {
          allowed = rate_limiter_->RequestToken(
              buf.Capacity() - buf.CurrentSize(), buf.Alignment(),
              Env::IOPriority::IO_LOW, stats_, RateLimiter::OpType::kRead);
        } else {
          assert(buf.CurrentSize() == 0);
          allowed = read_size;
        }
        Slice tmp;

        FileOperationInfo::TimePoint start_ts;
        uint64_t orig_offset = 0;
        if (ShouldNotifyListeners()) {
          start_ts = std::chrono::system_clock::now();
          orig_offset = aligned_offset + buf.CurrentSize();
        }
        {
          IOSTATS_CPU_TIMER_GUARD(cpu_read_nanos, env_);
          s = file_->Read(aligned_offset + buf.CurrentSize(), allowed,
                          IOOptions(), &tmp, buf.Destination(), nullptr);
        }
        if (ShouldNotifyListeners()) {
          auto finish_ts = std::chrono::system_clock::now();
          NotifyOnFileReadFinish(orig_offset, tmp.size(), start_ts, finish_ts,
                                 s);
        }

        buf.Size(buf.CurrentSize() + tmp.size());
        if (!s.ok() || tmp.size() < allowed) {
          break;
        }
      }
      size_t res_len = 0;
      if (s.ok() && offset_advance < buf.CurrentSize()) {
        res_len = buf.Read(scratch, offset_advance,
                           std::min(buf.CurrentSize() - offset_advance, n));
      }
      *result = Slice(scratch, res_len);
#endif  // !ROCKSDB_LITE
    } else {
      size_t pos = 0;
      const char* res_scratch = nullptr;
      while (pos < n) {
        size_t allowed;
        if (for_compaction && rate_limiter_ != nullptr) {
          if (rate_limiter_->IsRateLimited(RateLimiter::OpType::kRead)) {
            sw.DelayStart();
          }
          allowed = rate_limiter_->RequestToken(n - pos, 0 /* alignment */,
                                                Env::IOPriority::IO_LOW, stats_,
                                                RateLimiter::OpType::kRead);
          if (rate_limiter_->IsRateLimited(RateLimiter::OpType::kRead)) {
            sw.DelayStop();
          }
        } else {
          allowed = n;
        }
        Slice tmp_result;

#ifndef ROCKSDB_LITE
        FileOperationInfo::TimePoint start_ts;
        if (ShouldNotifyListeners()) {
          start_ts = std::chrono::system_clock::now();
        }
#endif
        {
          IOSTATS_CPU_TIMER_GUARD(cpu_read_nanos, env_);
          s = file_->Read(offset + pos, allowed, IOOptions(), &tmp_result,
                          scratch + pos, nullptr);
        }
#ifndef ROCKSDB_LITE
        if (ShouldNotifyListeners()) {
          auto finish_ts = std::chrono::system_clock::now();
          NotifyOnFileReadFinish(offset + pos, tmp_result.size(), start_ts,
                                 finish_ts, s);
        }
#endif

        if (res_scratch == nullptr) {
          // we can't simply use `scratch` because reads of mmap'd files return
          // data in a different buffer.
          res_scratch = tmp_result.data();
        } else {
          // make sure chunks are inserted contiguously into `res_scratch`.
          assert(tmp_result.data() == res_scratch + pos);
        }
        pos += tmp_result.size();
        if (!s.ok() || tmp_result.size() < allowed) {
          break;
        }
      }
      *result = Slice(res_scratch, s.ok() ? pos : 0);
    }
    IOSTATS_ADD_IF_POSITIVE(bytes_read, result->size());
    SetPerfLevel(prev_perf_level);
  }
  if (stats_ != nullptr && file_read_hist_ != nullptr) {
    file_read_hist_->Add(elapsed);
  }

  return s;
}

Status RandomAccessFileReader::MultiRead(FSReadRequest* read_reqs,
                                         size_t num_reqs) const {
  Status s;
  uint64_t elapsed = 0;
  assert(!use_direct_io());
  {
    StopWatch sw(env_, stats_, hist_type_,
                 (stats_ != nullptr) ? &elapsed : nullptr, true /*overwrite*/,
                 true /*delay_enabled*/);
    auto prev_perf_level = GetPerfLevel();
    IOSTATS_TIMER_GUARD(read_nanos);

#ifndef ROCKSDB_LITE
    FileOperationInfo::TimePoint start_ts;
    if (ShouldNotifyListeners()) {
      start_ts = std::chrono::system_clock::now();
    }
#endif  // ROCKSDB_LITE
    {
      IOSTATS_CPU_TIMER_GUARD(cpu_read_nanos, env_);
      s = file_->MultiRead(read_reqs, num_reqs, IOOptions(), nullptr);
    }
    for (size_t i = 0; i < num_reqs; ++i) {
#ifndef ROCKSDB_LITE
      if (ShouldNotifyListeners()) {
        auto finish_ts = std::chrono::system_clock::now();
        NotifyOnFileReadFinish(read_reqs[i].offset, read_reqs[i].result.size(),
                               start_ts, finish_ts, read_reqs[i].status);
      }
#endif  // ROCKSDB_LITE
      IOSTATS_ADD_IF_POSITIVE(bytes_read, read_reqs[i].result.size());
    }
    SetPerfLevel(prev_perf_level);
  }
  if (stats_ != nullptr && file_read_hist_ != nullptr) {
    file_read_hist_->Add(elapsed);
  }

  return s;
}
}  // namespace rocksdb