rocksdb/file/random_access_file_reader.cc
anand76 afa2420c2b Introduce a new storage specific Env API (#5761)
Summary:
The current Env API encompasses both storage/file operations, as well as OS related operations. Most of the APIs return a Status, which does not have enough metadata about an error, such as whether its retry-able or not, scope (i.e fault domain) of the error etc., that may be required in order to properly handle a storage error. The file APIs also do not provide enough control over the IO SLA, such as timeout, prioritization, hinting about placement and redundancy etc.

This PR separates out the file/storage APIs from Env into a new FileSystem class. The APIs are updated to return an IOStatus with metadata about the error, as well as to take an IOOptions structure as input in order to allow more control over the IO.

The user can set both ```options.env``` and ```options.file_system``` to specify that RocksDB should use the former for OS related operations and the latter for storage operations. Internally, a ```CompositeEnvWrapper``` has been introduced that inherits from ```Env``` and redirects individual methods to either an ```Env``` implementation or the ```FileSystem``` as appropriate. When options are sanitized during ```DB::Open```, ```options.env``` is replaced with a newly allocated ```CompositeEnvWrapper``` instance if both env and file_system have been specified. This way, the rest of the RocksDB code can continue to function as before.

This PR also ports PosixEnv to the new API by splitting it into two - PosixEnv and PosixFileSystem. PosixEnv is defined as a sub-class of CompositeEnvWrapper, and threading/time functions are overridden with Posix specific implementations in order to avoid an extra level of indirection.

The ```CompositeEnvWrapper``` translates ```IOStatus``` return code to ```Status```, and sets the severity to ```kSoftError``` if the io_status is retryable. The error handling code in RocksDB can then recover the DB automatically.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5761

Differential Revision: D18868376

Pulled By: anand1976

fbshipit-source-id: 39efe18a162ea746fabac6360ff529baba48486f
2019-12-13 14:48:41 -08:00

190 lines
6.6 KiB
C++

// 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