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#include "ThreadPoolReader.h"
#include <Common/VersionNumber.h>
#include <Common/assert_cast.h>
#include <Common/Exception.h>
#include <Common/ProfileEvents.h>
#include <Common/CurrentMetrics.h>
#include <Common/Stopwatch.h>
#include <Common/setThreadName.h>
#include <Common/MemorySanitizer.h>
#include <Common/CurrentThread.h>
#include <Common/ThreadPool.h>
#include <Poco/Environment.h>
#include <base/errnoToString.h>
#include <Poco/Event.h>
#include <future>
#include <unistd.h>
#include <fcntl.h>
#if defined(OS_LINUX)
#include <sys/syscall.h>
#include <sys/uio.h>
/// We don't want to depend on specific glibc version.
#if !defined(RWF_NOWAIT)
#define RWF_NOWAIT 8
#endif
#if !defined(SYS_preadv2)
#if defined(__x86_64__)
#define SYS_preadv2 327
#elif defined(__aarch64__)
#define SYS_preadv2 286
#elif defined(__powerpc64__)
#define SYS_preadv2 380
#elif defined(__riscv)
#define SYS_preadv2 286
#else
#error "Unsupported architecture"
#endif
#endif
#endif
namespace ProfileEvents
{
extern const Event ThreadPoolReaderPageCacheHit;
extern const Event ThreadPoolReaderPageCacheHitBytes;
extern const Event ThreadPoolReaderPageCacheHitElapsedMicroseconds;
extern const Event ThreadPoolReaderPageCacheMiss;
extern const Event ThreadPoolReaderPageCacheMissBytes;
extern const Event ThreadPoolReaderPageCacheMissElapsedMicroseconds;
extern const Event ReadBufferFromFileDescriptorRead;
extern const Event ReadBufferFromFileDescriptorReadFailed;
extern const Event ReadBufferFromFileDescriptorReadBytes;
extern const Event DiskReadElapsedMicroseconds;
}
namespace CurrentMetrics
{
extern const Metric Read;
extern const Metric ThreadPoolFSReaderThreads;
extern const Metric ThreadPoolFSReaderThreadsActive;
}
namespace DB
{
namespace ErrorCodes
{
extern const int CANNOT_READ_FROM_FILE_DESCRIPTOR;
}
#if defined(OS_LINUX)
/// According to man, Linux 5.9 and 5.10 have a bug in preadv2() with the RWF_NOWAIT.
/// https://manpages.debian.org/testing/manpages-dev/preadv2.2.en.html#BUGS
/// We also disable it for older Linux kernels, because according to user's reports, RedHat-patched kernels might be also affected.
static bool hasBugInPreadV2()
{
VersionNumber linux_version(Poco::Environment::osVersion());
return linux_version < VersionNumber{5, 11, 0};
}
#endif
ThreadPoolReader::ThreadPoolReader(size_t pool_size, size_t queue_size_)
: pool(std::make_unique<ThreadPool>(CurrentMetrics::ThreadPoolFSReaderThreads, CurrentMetrics::ThreadPoolFSReaderThreadsActive, pool_size, pool_size, queue_size_))
{
}
std::future<IAsynchronousReader::Result> ThreadPoolReader::submit(Request request)
{
/// If size is zero, then read() cannot be distinguished from EOF
assert(request.size);
int fd = assert_cast<const LocalFileDescriptor &>(*request.descriptor).fd;
#if defined(OS_LINUX)
/// Check if data is already in page cache with preadv2 syscall.
/// We don't want to depend on new Linux kernel.
/// But kernels 5.9 and 5.10 have a bug where preadv2() with the
/// RWF_NOWAIT flag may return 0 even when not at end of file.
/// It can't be distinguished from the real eof, so we have to
/// disable pread with nowait.
static std::atomic<bool> has_pread_nowait_support = !hasBugInPreadV2();
if (has_pread_nowait_support.load(std::memory_order_relaxed))
{
/// It reports real time spent including the time spent while thread was preempted doing nothing.
/// And it is Ok for the purpose of this watch (it is used to lower the number of threads to read from tables).
/// Sometimes it is better to use taskstats::blkio_delay_total, but it is quite expensive to get it
/// (NetlinkMetricsProvider has about 500K RPS).
Stopwatch watch(CLOCK_MONOTONIC);
SCOPE_EXIT({
watch.stop();
ProfileEvents::increment(ProfileEvents::ThreadPoolReaderPageCacheHitElapsedMicroseconds, watch.elapsedMicroseconds());
ProfileEvents::increment(ProfileEvents::DiskReadElapsedMicroseconds, watch.elapsedMicroseconds());
});
std::promise<Result> promise;
std::future<Result> future = promise.get_future();
size_t bytes_read = 0;
while (!bytes_read)
{
ssize_t res = 0;
{
CurrentMetrics::Increment metric_increment{CurrentMetrics::Read};
struct iovec io_vec{ .iov_base = request.buf, .iov_len = request.size };
res = syscall(
SYS_preadv2, fd,
&io_vec, 1,
/// This is kind of weird calling convention for syscall.
static_cast<int64_t>(request.offset), static_cast<int64_t>(request.offset >> 32),
/// This flag forces read from page cache or returning EAGAIN.
RWF_NOWAIT);
}
if (!res)
{
/// The file has ended.
promise.set_value({0, 0, nullptr});
return future;
}
if (-1 == res)
{
if (errno == ENOSYS || errno == EOPNOTSUPP)
{
/// No support for the syscall or the flag in the Linux kernel.
has_pread_nowait_support.store(false, std::memory_order_relaxed);
break;
}
else if (errno == EAGAIN)
{
/// Data is not available in page cache. Will hand off to thread pool.
break;
}
else if (errno == EINTR)
{
/// Interrupted by a signal.
continue;
}
else
{
ProfileEvents::increment(ProfileEvents::ReadBufferFromFileDescriptorReadFailed);
promise.set_exception(std::make_exception_ptr(ErrnoException(
fmt::format("Cannot read from file {}, {}", fd, errnoToString()),
ErrorCodes::CANNOT_READ_FROM_FILE_DESCRIPTOR, errno)));
return future;
}
}
else
{
bytes_read += res;
__msan_unpoison(request.buf, res);
}
}
if (bytes_read)
{
/// Read successfully from page cache.
ProfileEvents::increment(ProfileEvents::ThreadPoolReaderPageCacheHit);
ProfileEvents::increment(ProfileEvents::ThreadPoolReaderPageCacheHitBytes, bytes_read);
ProfileEvents::increment(ProfileEvents::ReadBufferFromFileDescriptorReadBytes, bytes_read);
promise.set_value({bytes_read, request.ignore, nullptr});
return future;
}
}
#endif
ProfileEvents::increment(ProfileEvents::ThreadPoolReaderPageCacheMiss);
auto schedule = threadPoolCallbackRunner<Result>(*pool, "ThreadPoolRead");
return schedule([request, fd]() -> Result
{
Stopwatch watch(CLOCK_MONOTONIC);
SCOPE_EXIT({
watch.stop();
ProfileEvents::increment(ProfileEvents::ThreadPoolReaderPageCacheMissElapsedMicroseconds, watch.elapsedMicroseconds());
ProfileEvents::increment(ProfileEvents::DiskReadElapsedMicroseconds, watch.elapsedMicroseconds());
});
size_t bytes_read = 0;
while (!bytes_read)
{
ssize_t res = 0;
{
CurrentMetrics::Increment metric_increment{CurrentMetrics::Read};
res = ::pread(fd, request.buf, request.size, request.offset);
}
/// File has ended.
if (!res)
break;
if (-1 == res && errno != EINTR)
{
ProfileEvents::increment(ProfileEvents::ReadBufferFromFileDescriptorReadFailed);
throwFromErrno(fmt::format("Cannot read from file {}", fd), ErrorCodes::CANNOT_READ_FROM_FILE_DESCRIPTOR);
}
bytes_read += res;
}
watch.stop();
ProfileEvents::increment(ProfileEvents::ThreadPoolReaderPageCacheMissBytes, bytes_read);
ProfileEvents::increment(ProfileEvents::ReadBufferFromFileDescriptorReadBytes, bytes_read);
return Result{ .size = bytes_read, .offset = request.ignore };
}, request.priority);
}
void ThreadPoolReader::wait()
{
pool->wait();
}
}
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