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rocksdb/file/random_access_file_reader.cc

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// 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 "file/file_util.h"
#include "monitoring/histogram.h"
#include "monitoring/iostats_context_imp.h"
#include "port/port.h"
#include "table/format.h"
#include "test_util/sync_point.h"
#include "util/random.h"
#include "util/rate_limiter_impl.h"
namespace ROCKSDB_NAMESPACE {
inline Histograms GetFileReadHistograms(Statistics* stats,
Env::IOActivity io_activity) {
switch (io_activity) {
case Env::IOActivity::kFlush:
return Histograms::FILE_READ_FLUSH_MICROS;
case Env::IOActivity::kCompaction:
return Histograms::FILE_READ_COMPACTION_MICROS;
case Env::IOActivity::kDBOpen:
return Histograms::FILE_READ_DB_OPEN_MICROS;
default:
break;
}
if (stats && stats->get_stats_level() > StatsLevel::kExceptDetailedTimers) {
switch (io_activity) {
case Env::IOActivity::kGet:
return Histograms::FILE_READ_GET_MICROS;
case Env::IOActivity::kMultiGet:
return Histograms::FILE_READ_MULTIGET_MICROS;
case Env::IOActivity::kDBIterator:
return Histograms::FILE_READ_DB_ITERATOR_MICROS;
case Env::IOActivity::kVerifyDBChecksum:
return Histograms::FILE_READ_VERIFY_DB_CHECKSUM_MICROS;
case Env::IOActivity::kVerifyFileChecksums:
return Histograms::FILE_READ_VERIFY_FILE_CHECKSUMS_MICROS;
default:
break;
}
}
return Histograms::HISTOGRAM_ENUM_MAX;
}
inline void RecordIOStats(Statistics* stats, Temperature file_temperature,
bool is_last_level, size_t size) {
IOSTATS_ADD(bytes_read, size);
// record for last/non-last level
if (is_last_level) {
RecordTick(stats, LAST_LEVEL_READ_BYTES, size);
RecordTick(stats, LAST_LEVEL_READ_COUNT, 1);
} else {
RecordTick(stats, NON_LAST_LEVEL_READ_BYTES, size);
RecordTick(stats, NON_LAST_LEVEL_READ_COUNT, 1);
}
// record for temperature file
if (file_temperature != Temperature::kUnknown) {
switch (file_temperature) {
case Temperature::kHot:
IOSTATS_ADD(file_io_stats_by_temperature.hot_file_bytes_read, size);
IOSTATS_ADD(file_io_stats_by_temperature.hot_file_read_count, 1);
RecordTick(stats, HOT_FILE_READ_BYTES, size);
RecordTick(stats, HOT_FILE_READ_COUNT, 1);
break;
case Temperature::kWarm:
IOSTATS_ADD(file_io_stats_by_temperature.warm_file_bytes_read, size);
IOSTATS_ADD(file_io_stats_by_temperature.warm_file_read_count, 1);
RecordTick(stats, WARM_FILE_READ_BYTES, size);
RecordTick(stats, WARM_FILE_READ_COUNT, 1);
break;
case Temperature::kCold:
IOSTATS_ADD(file_io_stats_by_temperature.cold_file_bytes_read, size);
IOSTATS_ADD(file_io_stats_by_temperature.cold_file_read_count, 1);
RecordTick(stats, COLD_FILE_READ_BYTES, size);
RecordTick(stats, COLD_FILE_READ_COUNT, 1);
break;
default:
break;
}
}
}
IOStatus RandomAccessFileReader::Create(
const std::shared_ptr<FileSystem>& fs, const std::string& fname,
const FileOptions& file_opts,
std::unique_ptr<RandomAccessFileReader>* reader, IODebugContext* dbg) {
std::unique_ptr<FSRandomAccessFile> file;
IOStatus io_s = fs->NewRandomAccessFile(fname, file_opts, &file, dbg);
if (io_s.ok()) {
reader->reset(new RandomAccessFileReader(std::move(file), fname));
}
return io_s;
}
IOStatus RandomAccessFileReader::Read(const IOOptions& opts, uint64_t offset,
size_t n, Slice* result, char* scratch,
AlignedBuf* aligned_buf) const {
(void)aligned_buf;
const Env::IOPriority rate_limiter_priority = opts.rate_limiter_priority;
TEST_SYNC_POINT_CALLBACK("RandomAccessFileReader::Read", nullptr);
// To be paranoid: modify scratch a little bit, so in case underlying
// FileSystem doesn't fill the buffer but return success and `scratch` returns
// contains a previous block, returned value will not pass checksum.
if (n > 0 && scratch != nullptr) {
// This byte might not change anything for direct I/O case, but it's OK.
scratch[0]++;
}
IOStatus io_s;
uint64_t elapsed = 0;
size_t alignment = file_->GetRequiredBufferAlignment();
bool is_aligned = false;
if (scratch != nullptr) {
// Check if offset, length and buffer are aligned.
is_aligned = (offset & (alignment - 1)) == 0 &&
(n & (alignment - 1)) == 0 &&
(uintptr_t(scratch) & (alignment - 1)) == 0;
}
{
StopWatch sw(clock_, stats_, hist_type_,
GetFileReadHistograms(stats_, opts.io_activity),
(stats_ != nullptr) ? &elapsed : nullptr, true /*overwrite*/,
true /*delay_enabled*/);
auto prev_perf_level = GetPerfLevel();
IOSTATS_TIMER_GUARD(read_nanos);
if (use_direct_io() && is_aligned == false) {
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 (rate_limiter_priority != Env::IO_TOTAL &&
rate_limiter_ != nullptr) {
allowed = rate_limiter_->RequestToken(
buf.Capacity() - buf.CurrentSize(), buf.Alignment(),
rate_limiter_priority, stats_, RateLimiter::OpType::kRead);
} else {
assert(buf.CurrentSize() == 0);
allowed = read_size;
}
Slice tmp;
FileOperationInfo::StartTimePoint start_ts;
uint64_t orig_offset = 0;
if (ShouldNotifyListeners()) {
start_ts = FileOperationInfo::StartNow();
orig_offset = aligned_offset + buf.CurrentSize();
}
{
IOSTATS_CPU_TIMER_GUARD(cpu_read_nanos, clock_);
// Only user reads are expected to specify a timeout. And user reads
// are not subjected to rate_limiter and should go through only
// one iteration of this loop, so we don't need to check and adjust
// the opts.timeout before calling file_->Read
assert(!opts.timeout.count() || allowed == read_size);
io_s = file_->Read(aligned_offset + buf.CurrentSize(), allowed, opts,
&tmp, buf.Destination(), nullptr);
}
if (ShouldNotifyListeners()) {
auto finish_ts = FileOperationInfo::FinishNow();
NotifyOnFileReadFinish(orig_offset, tmp.size(), start_ts, finish_ts,
io_s);
if (!io_s.ok()) {
NotifyOnIOError(io_s, FileOperationType::kRead, file_name(),
tmp.size(), orig_offset);
}
}
buf.Size(buf.CurrentSize() + tmp.size());
if (!io_s.ok() || tmp.size() < allowed) {
break;
}
}
size_t res_len = 0;
if (io_s.ok() && offset_advance < buf.CurrentSize()) {
res_len = std::min(buf.CurrentSize() - offset_advance, n);
if (aligned_buf == nullptr) {
buf.Read(scratch, offset_advance, res_len);
} else {
scratch = buf.BufferStart() + offset_advance;
aligned_buf->reset(buf.Release());
}
}
*result = Slice(scratch, res_len);
} else {
size_t pos = 0;
const char* res_scratch = nullptr;
while (pos < n) {
size_t allowed;
if (rate_limiter_priority != Env::IO_TOTAL &&
rate_limiter_ != nullptr) {
if (rate_limiter_->IsRateLimited(RateLimiter::OpType::kRead)) {
sw.DelayStart();
}
allowed = rate_limiter_->RequestToken(
n - pos, (use_direct_io() ? alignment : 0), rate_limiter_priority,
stats_, RateLimiter::OpType::kRead);
if (rate_limiter_->IsRateLimited(RateLimiter::OpType::kRead)) {
sw.DelayStop();
}
} else {
allowed = n;
}
Slice tmp_result;
FileOperationInfo::StartTimePoint start_ts;
if (ShouldNotifyListeners()) {
start_ts = FileOperationInfo::StartNow();
}
{
IOSTATS_CPU_TIMER_GUARD(cpu_read_nanos, clock_);
// Only user reads are expected to specify a timeout. And user reads
// are not subjected to rate_limiter and should go through only
// one iteration of this loop, so we don't need to check and adjust
// the opts.timeout before calling file_->Read
assert(!opts.timeout.count() || allowed == n);
io_s = file_->Read(offset + pos, allowed, opts, &tmp_result,
scratch + pos, nullptr);
}
if (ShouldNotifyListeners()) {
auto finish_ts = FileOperationInfo::FinishNow();
NotifyOnFileReadFinish(offset + pos, tmp_result.size(), start_ts,
finish_ts, io_s);
if (!io_s.ok()) {
NotifyOnIOError(io_s, FileOperationType::kRead, file_name(),
tmp_result.size(), offset + pos);
}
}
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 (!io_s.ok() || tmp_result.size() < allowed) {
break;
}
}
*result = Slice(res_scratch, io_s.ok() ? pos : 0);
}
RecordIOStats(stats_, file_temperature_, is_last_level_, result->size());
SetPerfLevel(prev_perf_level);
}
if (stats_ != nullptr && file_read_hist_ != nullptr) {
file_read_hist_->Add(elapsed);
}
#ifndef NDEBUG
auto pair = std::make_pair(&file_name_, &io_s);
if (offset == 0) {
TEST_SYNC_POINT_CALLBACK("RandomAccessFileReader::Read::BeforeReturn",
&pair);
}
TEST_SYNC_POINT_CALLBACK("RandomAccessFileReader::Read::AnyOffset", &pair);
#endif
return io_s;
}
size_t End(const FSReadRequest& r) {
return static_cast<size_t>(r.offset) + r.len;
}
FSReadRequest Align(const FSReadRequest& r, size_t alignment) {
FSReadRequest req;
req.offset = static_cast<uint64_t>(
TruncateToPageBoundary(alignment, static_cast<size_t>(r.offset)));
req.len = Roundup(End(r), alignment) - req.offset;
req.scratch = nullptr;
return req;
}
bool TryMerge(FSReadRequest* dest, const FSReadRequest& src) {
size_t dest_offset = static_cast<size_t>(dest->offset);
size_t src_offset = static_cast<size_t>(src.offset);
size_t dest_end = End(*dest);
size_t src_end = End(src);
if (std::max(dest_offset, src_offset) > std::min(dest_end, src_end)) {
return false;
}
dest->offset = static_cast<uint64_t>(std::min(dest_offset, src_offset));
dest->len = std::max(dest_end, src_end) - dest->offset;
return true;
}
IOStatus RandomAccessFileReader::MultiRead(const IOOptions& opts,
FSReadRequest* read_reqs,
size_t num_reqs,
AlignedBuf* aligned_buf) const {
(void)aligned_buf; // suppress warning of unused variable in LITE mode
assert(num_reqs > 0);
#ifndef NDEBUG
for (size_t i = 0; i < num_reqs - 1; ++i) {
assert(read_reqs[i].offset <= read_reqs[i + 1].offset);
}
#endif // !NDEBUG
const Env::IOPriority rate_limiter_priority = opts.rate_limiter_priority;
// To be paranoid modify scratch a little bit, so in case underlying
// FileSystem doesn't fill the buffer but return success and `scratch` returns
// contains a previous block, returned value will not pass checksum.
// This byte might not change anything for direct I/O case, but it's OK.
for (size_t i = 0; i < num_reqs; i++) {
FSReadRequest& r = read_reqs[i];
if (r.len > 0 && r.scratch != nullptr) {
r.scratch[0]++;
}
}
IOStatus io_s;
uint64_t elapsed = 0;
{
StopWatch sw(clock_, stats_, hist_type_,
GetFileReadHistograms(stats_, opts.io_activity),
(stats_ != nullptr) ? &elapsed : nullptr, true /*overwrite*/,
true /*delay_enabled*/);
auto prev_perf_level = GetPerfLevel();
IOSTATS_TIMER_GUARD(read_nanos);
FSReadRequest* fs_reqs = read_reqs;
size_t num_fs_reqs = num_reqs;
std::vector<FSReadRequest> aligned_reqs;
if (use_direct_io()) {
// num_reqs is the max possible size,
// this can reduce std::vecector's internal resize operations.
aligned_reqs.reserve(num_reqs);
// Align and merge the read requests.
size_t alignment = file_->GetRequiredBufferAlignment();
for (size_t i = 0; i < num_reqs; i++) {
FSReadRequest r = Align(read_reqs[i], alignment);
if (i == 0) {
// head
aligned_reqs.push_back(std::move(r));
} else if (!TryMerge(&aligned_reqs.back(), r)) {
// head + n
aligned_reqs.push_back(std::move(r));
} else {
// unused
r.status.PermitUncheckedError();
}
}
TEST_SYNC_POINT_CALLBACK("RandomAccessFileReader::MultiRead:AlignedReqs",
&aligned_reqs);
// Allocate aligned buffer and let scratch buffers point to it.
size_t total_len = 0;
for (const auto& r : aligned_reqs) {
total_len += r.len;
}
AlignedBuffer buf;
buf.Alignment(alignment);
buf.AllocateNewBuffer(total_len);
char* scratch = buf.BufferStart();
for (auto& r : aligned_reqs) {
r.scratch = scratch;
scratch += r.len;
}
aligned_buf->reset(buf.Release());
fs_reqs = aligned_reqs.data();
num_fs_reqs = aligned_reqs.size();
}
FileOperationInfo::StartTimePoint start_ts;
if (ShouldNotifyListeners()) {
start_ts = FileOperationInfo::StartNow();
}
{
IOSTATS_CPU_TIMER_GUARD(cpu_read_nanos, clock_);
if (rate_limiter_priority != Env::IO_TOTAL && rate_limiter_ != nullptr) {
// TODO: ideally we should call `RateLimiter::RequestToken()` for
// allowed bytes to multi-read and then consume those bytes by
// satisfying as many requests in `MultiRead()` as possible, instead of
// what we do here, which can cause burst when the
// `total_multi_read_size` is big.
size_t total_multi_read_size = 0;
assert(fs_reqs != nullptr);
for (size_t i = 0; i < num_fs_reqs; ++i) {
FSReadRequest& req = fs_reqs[i];
total_multi_read_size += req.len;
}
size_t remaining_bytes = total_multi_read_size;
size_t request_bytes = 0;
while (remaining_bytes > 0) {
request_bytes = std::min(
static_cast<size_t>(rate_limiter_->GetSingleBurstBytes()),
remaining_bytes);
rate_limiter_->Request(request_bytes, rate_limiter_priority,
nullptr /* stats */,
RateLimiter::OpType::kRead);
remaining_bytes -= request_bytes;
}
}
io_s = file_->MultiRead(fs_reqs, num_fs_reqs, opts, nullptr);
RecordInHistogram(stats_, MULTIGET_IO_BATCH_SIZE, num_fs_reqs);
}
if (use_direct_io()) {
// Populate results in the unaligned read requests.
size_t aligned_i = 0;
for (size_t i = 0; i < num_reqs; i++) {
auto& r = read_reqs[i];
if (static_cast<size_t>(r.offset) > End(aligned_reqs[aligned_i])) {
aligned_i++;
}
const auto& fs_r = fs_reqs[aligned_i];
r.status = fs_r.status;
if (r.status.ok()) {
uint64_t offset = r.offset - fs_r.offset;
if (fs_r.result.size() <= offset) {
// No byte in the read range is returned.
r.result = Slice();
} else {
size_t len = std::min(
r.len, static_cast<size_t>(fs_r.result.size() - offset));
r.result = Slice(fs_r.scratch + offset, len);
}
} else {
r.result = Slice();
}
}
}
for (size_t i = 0; i < num_reqs; ++i) {
if (ShouldNotifyListeners()) {
auto finish_ts = FileOperationInfo::FinishNow();
NotifyOnFileReadFinish(read_reqs[i].offset, read_reqs[i].result.size(),
start_ts, finish_ts, read_reqs[i].status);
}
if (!read_reqs[i].status.ok()) {
NotifyOnIOError(read_reqs[i].status, FileOperationType::kRead,
file_name(), read_reqs[i].result.size(),
read_reqs[i].offset);
}
RecordIOStats(stats_, file_temperature_, is_last_level_,
read_reqs[i].result.size());
}
SetPerfLevel(prev_perf_level);
}
if (stats_ != nullptr && file_read_hist_ != nullptr) {
file_read_hist_->Add(elapsed);
}
return io_s;
}
IOStatus RandomAccessFileReader::PrepareIOOptions(const ReadOptions& ro,
IOOptions& opts) const {
if (clock_ != nullptr) {
return PrepareIOFromReadOptions(ro, clock_, opts);
} else {
return PrepareIOFromReadOptions(ro, SystemClock::Default().get(), opts);
}
}
IOStatus RandomAccessFileReader::ReadAsync(
FSReadRequest& req, const IOOptions& opts,
std::function<void(const FSReadRequest&, void*)> cb, void* cb_arg,
void** io_handle, IOHandleDeleter* del_fn, AlignedBuf* aligned_buf) {
IOStatus s;
// Create a callback and populate info.
auto read_async_callback =
std::bind(&RandomAccessFileReader::ReadAsyncCallback, this,
std::placeholders::_1, std::placeholders::_2);
ReadAsyncInfo* read_async_info =
new ReadAsyncInfo(cb, cb_arg, clock_->NowMicros());
if (ShouldNotifyListeners()) {
read_async_info->fs_start_ts_ = FileOperationInfo::StartNow();
}
size_t alignment = file_->GetRequiredBufferAlignment();
bool is_aligned = (req.offset & (alignment - 1)) == 0 &&
(req.len & (alignment - 1)) == 0 &&
(uintptr_t(req.scratch) & (alignment - 1)) == 0;
read_async_info->is_aligned_ = is_aligned;
uint64_t elapsed = 0;
if (use_direct_io() && is_aligned == false) {
FSReadRequest aligned_req = Align(req, alignment);
aligned_req.status.PermitUncheckedError();
// Allocate aligned buffer.
read_async_info->buf_.Alignment(alignment);
read_async_info->buf_.AllocateNewBuffer(aligned_req.len);
// Set rem fields in aligned FSReadRequest.
aligned_req.scratch = read_async_info->buf_.BufferStart();
// Set user provided fields to populate back in callback.
read_async_info->user_scratch_ = req.scratch;
read_async_info->user_aligned_buf_ = aligned_buf;
read_async_info->user_len_ = req.len;
read_async_info->user_offset_ = req.offset;
read_async_info->user_result_ = req.result;
assert(read_async_info->buf_.CurrentSize() == 0);
StopWatch sw(clock_, stats_, hist_type_,
GetFileReadHistograms(stats_, opts.io_activity),
(stats_ != nullptr) ? &elapsed : nullptr, true /*overwrite*/,
true /*delay_enabled*/);
s = file_->ReadAsync(aligned_req, opts, read_async_callback,
read_async_info, io_handle, del_fn, nullptr /*dbg*/);
} else {
StopWatch sw(clock_, stats_, hist_type_,
GetFileReadHistograms(stats_, opts.io_activity),
(stats_ != nullptr) ? &elapsed : nullptr, true /*overwrite*/,
true /*delay_enabled*/);
s = file_->ReadAsync(req, opts, read_async_callback, read_async_info,
io_handle, del_fn, nullptr /*dbg*/);
}
RecordTick(stats_, READ_ASYNC_MICROS, elapsed);
// Suppress false positive clang analyzer warnings.
// Memory is not released if file_->ReadAsync returns !s.ok(), because
// ReadAsyncCallback is never called in that case. If ReadAsyncCallback is
// called then ReadAsync should always return IOStatus::OK().
#ifndef __clang_analyzer__
if (!s.ok()) {
delete read_async_info;
}
#endif // __clang_analyzer__
return s;
}
void RandomAccessFileReader::ReadAsyncCallback(const FSReadRequest& req,
void* cb_arg) {
ReadAsyncInfo* read_async_info = static_cast<ReadAsyncInfo*>(cb_arg);
assert(read_async_info);
assert(read_async_info->cb_);
if (use_direct_io() && read_async_info->is_aligned_ == false) {
// Create FSReadRequest with user provided fields.
FSReadRequest user_req;
user_req.scratch = read_async_info->user_scratch_;
user_req.offset = read_async_info->user_offset_;
user_req.len = read_async_info->user_len_;
// Update results in user_req.
user_req.result = req.result;
user_req.status = req.status;
read_async_info->buf_.Size(read_async_info->buf_.CurrentSize() +
req.result.size());
size_t offset_advance_len = static_cast<size_t>(
/*offset_passed_by_user=*/read_async_info->user_offset_ -
/*aligned_offset=*/req.offset);
size_t res_len = 0;
if (req.status.ok() &&
offset_advance_len < read_async_info->buf_.CurrentSize()) {
res_len =
std::min(read_async_info->buf_.CurrentSize() - offset_advance_len,
read_async_info->user_len_);
if (read_async_info->user_aligned_buf_ == nullptr) {
// Copy the data into user's scratch.
// Clang analyzer assumes that it will take use_direct_io() == false in
// ReadAsync and use_direct_io() == true in Callback which cannot be true.
#ifndef __clang_analyzer__
read_async_info->buf_.Read(user_req.scratch, offset_advance_len,
res_len);
#endif // __clang_analyzer__
} else {
// Set aligned_buf provided by user without additional copy.
user_req.scratch =
read_async_info->buf_.BufferStart() + offset_advance_len;
read_async_info->user_aligned_buf_->reset(
read_async_info->buf_.Release());
}
user_req.result = Slice(user_req.scratch, res_len);
} else {
// Either req.status is not ok or data was not read.
user_req.result = Slice();
}
read_async_info->cb_(user_req, read_async_info->cb_arg_);
} else {
read_async_info->cb_(req, read_async_info->cb_arg_);
}
// Update stats and notify listeners.
if (stats_ != nullptr && file_read_hist_ != nullptr) {
// elapsed doesn't take into account delay and overwrite as StopWatch does
// in Read.
uint64_t elapsed = clock_->NowMicros() - read_async_info->start_time_;
file_read_hist_->Add(elapsed);
}
if (req.status.ok()) {
RecordInHistogram(stats_, ASYNC_READ_BYTES, req.result.size());
} else if (!req.status.IsAborted()) {
RecordTick(stats_, ASYNC_READ_ERROR_COUNT, 1);
}
if (ShouldNotifyListeners()) {
auto finish_ts = FileOperationInfo::FinishNow();
NotifyOnFileReadFinish(req.offset, req.result.size(),
read_async_info->fs_start_ts_, finish_ts,
req.status);
}
if (!req.status.ok()) {
NotifyOnIOError(req.status, FileOperationType::kRead, file_name(),
req.result.size(), req.offset);
}
RecordIOStats(stats_, file_temperature_, is_last_level_, req.result.size());
delete read_async_info;
}
} // namespace ROCKSDB_NAMESPACE
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