ClickHouse/src/Common/FileCache.cpp

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#include "FileCache.h"
#include <Common/randomSeed.h>
#include <Common/SipHash.h>
#include <Common/hex.h>
#include <IO/ReadHelpers.h>
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#include <IO/WriteBufferFromFile.h>
#include <IO/ReadSettings.h>
#include <IO/WriteBufferFromString.h>
#include <IO/Operators.h>
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#include <pcg-random/pcg_random.hpp>
#include <filesystem>
namespace fs = std::filesystem;
namespace DB
{
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namespace ErrorCodes
{
extern const int FILE_CACHE_ERROR;
}
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namespace
{
String keyToStr(const FileCache::Key & key)
{
return getHexUIntLowercase(key);
}
}
FileCache::FileCache(const String & cache_base_path_, size_t max_size_, size_t max_element_size_)
: cache_base_path(cache_base_path_), max_size(max_size_), max_element_size(max_element_size_)
{
}
FileCache::Key FileCache::hash(const String & path)
{
return sipHash128(path.data(), path.size());
}
String FileCache::path(const Key & key, size_t offset)
{
auto key_str = keyToStr(key);
return fs::path(cache_base_path) / key_str.substr(0, 3) / key_str / std::to_string(offset);
}
String FileCache::path(const Key & key)
{
auto key_str = keyToStr(key);
return fs::path(cache_base_path) / key_str.substr(0, 3) / key_str;
}
LRUFileCache::LRUFileCache(const String & cache_base_path_, size_t max_size_, size_t max_element_size_)
: FileCache(cache_base_path_, max_size_, max_element_size_), log(&Poco::Logger::get("LRUFileCache"))
{
if (fs::exists(cache_base_path))
restore();
else
fs::create_directories(cache_base_path);
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startup_restore_finished = true;
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}
void LRUFileCache::useCell(
const FileSegmentCell & cell, FileSegments & result, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
result.push_back(cell.file_segment);
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/**
* A cell receives a queue iterator on first successful space reservation attempt
* (space is reserved incrementally on each read buffer nextImpl() call).
*/
if (cell.queue_iterator)
{
/// Move to the end of the queue. The iterator remains valid.
queue.splice(queue.end(), queue, *cell.queue_iterator);
}
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}
LRUFileCache::FileSegmentCell * LRUFileCache::getCell(
const Key & key, size_t offset, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
auto it = files.find(key);
if (it == files.end())
return nullptr;
auto & offsets = it->second;
auto cell_it = offsets.find(offset);
if (cell_it == offsets.end())
return nullptr;
return &cell_it->second;
}
FileSegments LRUFileCache::getImpl(
const Key & key, const FileSegment::Range & range, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
/// Given range = [left, right] and non-overlapping ordered set of file segments,
/// find list [segment1, ..., segmentN] of segments which intersect with given range.
auto it = files.find(key);
if (it == files.end())
return {};
const auto & file_segments = it->second;
if (file_segments.empty())
{
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removeFileKey(key);
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return {};
}
FileSegments result;
auto segment_it = file_segments.lower_bound(range.left);
if (segment_it == file_segments.end())
{
/// N - last cached segment for given file key, segment{N}.offset < range.left:
/// segment{N} segment{N}
/// [________ [_______]
/// [__________] OR [________]
/// ^ ^
/// range.left range.left
const auto & cell = (--file_segments.end())->second;
if (cell.file_segment->range().right < range.left)
return {};
useCell(cell, result, cache_lock);
}
else /// segment_it <-- segmment{k}
{
if (segment_it != file_segments.begin())
{
const auto & prev_cell = std::prev(segment_it)->second;
const auto & prev_cell_range = prev_cell.file_segment->range();
if (range.left <= prev_cell_range.right)
{
/// segment{k-1} segment{k}
/// [________] [_____
/// [___________
/// ^
/// range.left
useCell(prev_cell, result, cache_lock);
}
}
/// segment{k} ... segment{k-1} segment{k} segment{k}
/// [______ [______] [____ [________
/// [_________ OR [________ OR [______] ^
/// ^ ^ ^ segment{k}.offset
/// range.left range.left range.right
while (segment_it != file_segments.end())
{
const auto & cell = segment_it->second;
if (range.right < cell.file_segment->range().left)
break;
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useCell(cell, result, cache_lock);
++segment_it;
}
}
/// TODO: remove this extra debug logging.
String ranges;
for (const auto & s : result)
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ranges += "\nRange: " + s->range().toString() + ", download state: " + FileSegment::toString(s->state()) + " ";
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LOG_TEST(log, "Cache get. Key: {}, range: {}, file_segments number: {}, ranges: {}",
keyToStr(key), range.toString(), result.size(), ranges);
return result;
}
FileSegmentsHolder LRUFileCache::getOrSet(const Key & key, size_t offset, size_t size)
{
FileSegment::Range range(offset, offset + size - 1);
std::lock_guard cache_lock(mutex);
/// Get all segments which intersect with the given range.
auto file_segments = getImpl(key, range, cache_lock);
if (file_segments.empty())
{
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auto * cell = setImpl(key, offset, size, FileSegment::State::EMPTY, cache_lock);
file_segments = {cell->file_segment};
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}
else
{
/// There are segments [segment1, ..., segmentN]
/// (non-overlapping, non-empty, ascending-ordered) which (maybe partially)
/// intersect with given range.
/// It can have holes:
/// [____________________] -- requested range
/// [____] [_] [_________] -- intersecting cache [segment1, ..., segmentN]
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///
/// For each such hole create a cell with file segment state EMPTY.
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auto it = file_segments.begin();
auto segment_range = (*it)->range();
size_t current_pos;
if (segment_range.left < range.left)
{
/// [_______ -- requested range
/// [_______
/// ^
/// segment1
current_pos = segment_range.right + 1;
++it;
}
else
current_pos = range.left;
while (current_pos <= range.right && it != file_segments.end())
{
segment_range = (*it)->range();
if (current_pos == segment_range.left)
{
current_pos = segment_range.right + 1;
++it;
continue;
}
assert(current_pos < segment_range.left);
auto hole_size = segment_range.left - current_pos;
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auto * cell = setImpl(key, current_pos, hole_size, FileSegment::State::EMPTY, cache_lock);
file_segments.insert(it, cell->file_segment);
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current_pos = segment_range.right + 1;
++it;
}
if (current_pos <= range.right)
{
/// ________] -- requested range
/// _____]
/// ^
/// segmentN
auto hole_size = range.right - current_pos + 1;
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auto * cell = setImpl(key, current_pos, hole_size, FileSegment::State::EMPTY, cache_lock);
file_segments.push_back(cell->file_segment);
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}
}
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assert(!file_segments.empty());
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return FileSegmentsHolder(std::move(file_segments));
}
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LRUFileCache::FileSegmentCell * LRUFileCache::addCell(
const Key & key, size_t offset, size_t size, FileSegment::State state, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
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{
if (!size)
return nullptr; /// Empty files are not cached.
if (files[key].contains(offset))
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throw Exception(ErrorCodes::FILE_CACHE_ERROR,
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"Cache already exists for key: `{}`, offset: {}, size: {}", keyToStr(key), offset, size);
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auto file_segment = std::make_shared<FileSegment>(offset, size, key, this, state);
FileSegmentCell cell(std::move(file_segment));
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auto & offsets = files[key];
if (offsets.empty())
{
auto key_path = path(key);
if (!fs::exists(key_path))
fs::create_directories(key_path);
}
auto [it, inserted] = offsets.insert({offset, std::move(cell)});
if (!inserted)
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throw Exception(ErrorCodes::FILE_CACHE_ERROR,
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"Failed to insert into cache key: `{}`, offset: {}, size: {}", keyToStr(key), offset, size);
return &(it->second);
}
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bool LRUFileCache::set(
const Key & key, size_t offset, size_t size,
[[maybe_unused]] std::lock_guard<std::mutex> & segment_lock,
[[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
auto * cell = getCell(key, offset, cache_lock);
if (!cell)
throw Exception(ErrorCodes::FILE_CACHE_ERROR,
"Cannot set cell, because it was not created for key: {}, offset: {}", keyToStr(key), offset);
auto state = cell->file_segment->download_state;
return setImpl(key, offset, size, state, cache_lock) != nullptr;
}
LRUFileCache::FileSegmentCell * LRUFileCache::setImpl(
const Key & key, size_t offset, size_t size,
FileSegment::State state, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
if (!size)
return nullptr;
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LOG_TEST(log, "SetImpl. Key: {}, offset: {}, size: {}", keyToStr(key), offset, size);
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switch (state)
{
case FileSegment::State::EMPTY:
{
/**
* A new cell in cache becomes EMPTY at first, does not have any reserved space and
* is not present in LRUQueue, but are visible to cache users as a valid cache cell.
* EMPTY cells acquire DOWNLOADING state when it's owner successfully calls getOrSetDownlaoder()
* and are put into LRUQueue on first (successful) space reservation attempt.
*/
return addCell(key, offset, size, state, cache_lock);
}
case FileSegment::State::DOWNLOADED:
{
if (startup_restore_finished)
throw Exception(ErrorCodes::FILE_CACHE_ERROR, "Setting DOWNLOADED state cell is allowed only at startup");
if (tryReserve(size, cache_lock))
{
auto * cell = addCell(key, offset, size, state, cache_lock);
cell->queue_iterator = queue.insert(queue.end(), std::make_pair(key, offset));
return cell;
}
return nullptr;
}
case FileSegment::State::DOWNLOADING:
{
auto * cell = getCell(key, offset, cache_lock);
if (!cell)
throw Exception(ErrorCodes::FILE_CACHE_ERROR,
"Cannot set cell, because it was not created for key: {}, offset: {}", keyToStr(key), offset);
if (tryReserve(size, cache_lock))
{
cell->queue_iterator = queue.insert(queue.end(), std::make_pair(key, offset));
return cell;
}
return nullptr;
}
default:
throw Exception(ErrorCodes::FILE_CACHE_ERROR, "Unexpected state: {}", FileSegment::toString(state));
}
}
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bool LRUFileCache::tryReserve(size_t size, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
auto queue_size = queue.size() + 1;
auto removed_size = 0;
auto is_overflow = [&]
{
return (current_size + size - removed_size > max_size)
|| (max_element_size != 0 && queue_size > max_element_size);
};
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std::vector<FileKeyAndOffset> to_evict;
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auto key_it = queue.begin();
while (is_overflow() && key_it != queue.end())
{
const auto [key, offset] = *key_it++;
auto * cell = getCell(key, offset, cache_lock);
if (!cell)
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throw Exception(ErrorCodes::FILE_CACHE_ERROR,
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"Cache became inconsistent. Key: {}, offset: {}", keyToStr(key), offset);
size_t cell_size = cell->size();
/// It is guaranteed that cell is not removed from cache as long as
/// pointer to corresponding file segment is hold by any other thread.
if (cell->releasable())
{
switch (cell->file_segment->state())
{
case FileSegment::State::DOWNLOADED:
{
/// Cell will actually be removed only if
/// we managed to reserve enough space.
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to_evict.emplace_back(key, offset);
break;
}
case FileSegment::State::DOWNLOADING:
{
remove(key, offset, cache_lock);
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break;
}
default:
{
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remove(key, offset, cache_lock);
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break;
}
}
removed_size += cell_size;
--queue_size;
}
}
if (is_overflow())
return false;
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for (auto & [key, offset] : to_evict)
remove(key, offset, cache_lock);
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current_size += size - removed_size;
if (current_size > (1ull << 63))
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throw Exception(ErrorCodes::FILE_CACHE_ERROR, "Cache became inconsistent. There must be a bug");
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return true;
}
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void LRUFileCache::remove(
Key key, size_t offset, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
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{
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LOG_TEST(log, "Remove. Key: {}, offset: {}", keyToStr(key), offset);
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auto * cell = getCell(key, offset, cache_lock);
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if (!cell)
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throw Exception(ErrorCodes::FILE_CACHE_ERROR, "No cache cell for key: {}, offset: {}", keyToStr(key), offset);
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if (cell->queue_iterator)
queue.erase(*cell->queue_iterator);
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auto & offsets = files[key];
offsets.erase(offset);
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auto cache_file_path = path(key, offset);
if (fs::exists(cache_file_path))
{
try
{
fs::remove(cache_file_path);
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if (startup_restore_finished && offsets.empty())
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{
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removeFileKey(key);
return;
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}
}
catch (...)
{
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throw Exception(ErrorCodes::FILE_CACHE_ERROR,
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"Removal of cached file failed. Key: {}, offset: {}, path: {}, error: {}",
keyToStr(key), offset, cache_file_path, getCurrentExceptionMessage(false));
}
}
}
void LRUFileCache::restore()
{
std::lock_guard cache_lock(mutex);
Key key;
UInt64 offset;
size_t size;
std::vector<FileSegmentCell *> cells;
/// cache_base_path / key_prefix / key / offset
fs::directory_iterator key_prefix_it{cache_base_path};
for (; key_prefix_it != fs::directory_iterator(); ++key_prefix_it)
{
fs::directory_iterator key_it{key_prefix_it->path()};
for (; key_it != fs::directory_iterator(); ++key_it)
{
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key = unhexUInt<UInt128>(key_it->path().filename().string().data());
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fs::directory_iterator offset_it{key_it->path()};
for (; offset_it != fs::directory_iterator(); ++offset_it)
{
bool parsed = tryParse<UInt64>(offset, offset_it->path().filename());
if (!parsed)
throw Exception(
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ErrorCodes::FILE_CACHE_ERROR,
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"Unexpected file in cache: cannot parse offset. Path: {}", key_it->path().string());
size = offset_it->file_size();
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auto * cell = setImpl(key, offset, size, FileSegment::State::DOWNLOADED, cache_lock);
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if (cell)
{
cells.push_back(cell);
}
else
{
LOG_WARNING(log,
"Cache capacity changed (max size: {}, available: {}), cached file `{}` does not fit in cache anymore (size: {})",
max_size, available(), key_it->path().string(), size);
fs::remove(path(key, offset));
}
}
}
}
/// Shuffle cells to have random order in LRUQueue as at startup all cells have the same priority.
pcg64 generator(randomSeed());
std::shuffle(cells.begin(), cells.end(), generator);
for (const auto & cell : cells)
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queue.splice(queue.end(), queue, *cell->queue_iterator);
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}
void LRUFileCache::remove(const Key & key)
{
std::lock_guard cache_lock(mutex);
auto it = files.find(key);
if (it == files.end())
return;
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auto & offsets = it->second;
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for (auto & [offset, _] : offsets)
remove(key, offset, cache_lock);
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removeFileKey(key);
}
void LRUFileCache::removeFileKey(const Key & key)
{
auto key_path = path(key);
files.erase(key);
if (fs::exists(key_path))
fs::remove(key_path);
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}
LRUFileCache::Stat LRUFileCache::getStat()
{
std::lock_guard cache_lock(mutex);
Stat stat
{
.size = queue.size(),
.available = available(),
.downloaded_size = 0,
.downloading_size = 0,
};
for (const auto & [key, offset] : queue)
{
const auto * cell = getCell(key, offset, cache_lock);
if (!cell)
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throw Exception(ErrorCodes::FILE_CACHE_ERROR,
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"Cache became inconsistent. Key: {}, offset: {}", keyToStr(key), offset);
switch (cell->file_segment->state())
{
case FileSegment::State::DOWNLOADED:
{
++stat.downloaded_size;
break;
}
case FileSegment::State::DOWNLOADING:
{
++stat.downloading_size;
break;
}
default:
break;
}
}
return stat;
}
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size_t LRUFileCache::getUseCount(const FileSegment & file_segment,
[[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
auto * cell = getCell(file_segment.key(), file_segment.range().left, cache_lock);
assert(cell->file_segment.use_count() >= 1);
return cell->file_segment.use_count() - 1; /// Do not consider pointer which lies in cache itself.
}
String FileSegment::getCallerId()
{
if (!CurrentThread::isInitialized() || CurrentThread::getQueryId().size == 0)
throw Exception(ErrorCodes::FILE_CACHE_ERROR, "Cannot use cache without query id");
return CurrentThread::getQueryId().toString();
}
String FileSegment::getOrSetDownloader()
{
std::lock_guard segment_lock(mutex);
if (downloader_id.empty())
{
downloader_id = getCallerId();
download_state = State::DOWNLOADING;
}
return downloader_id;
}
bool FileSegment::isDownloader() const
{
std::lock_guard segment_lock(mutex);
return getCallerId() == downloader_id;
}
void FileSegment::write(const char * from, size_t size)
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{
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if (available() < size)
throw Exception(
ErrorCodes::FILE_CACHE_ERROR,
"Not enough space is reserved. Available: {}, expected: {}", available(), size);
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if (!download_buffer)
{
assert(!downloaded_size);
auto download_path = cache->path(key(), range().left);
download_buffer = std::make_unique<WriteBufferFromFile>(download_path);
}
download_buffer->write(from, size);
downloaded_size += size;
}
void FileSegment::complete()
{
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{
std::lock_guard segment_lock(mutex);
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/// TODO: There is a gap between next thread will call getOrSetDownlaoder and no one will remove the cell during this gap.
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if (downloader_id != getCallerId())
throw Exception(ErrorCodes::FILE_CACHE_ERROR,
"File segment can be completed only by downloader or downloader's FileSegmentsHodler");
downloader_id.clear();
download_buffer.reset();
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switch (download_state)
{
case State::EMPTY:
case State::DOWNLOADED:
{
/// Download not even started or already completed successfully.
break;
}
case State::NO_SPACE: /// Space reservation failed.
{
assert(!downloaded_size);
reserved_size = 0;
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std::lock_guard cache_lock(cache->mutex);
cache->remove(key(), range().left, cache_lock);
break;
}
case State::DOWNLOADING:
{
if (downloaded_size == range().size())
{
std::lock_guard cache_lock(cache->mutex);
download_state = State::DOWNLOADED;
reserved_size = downloaded_size;
}
else
{
/**
* If file segment downloader did not finish download completely, check if there is some other
* thread holding the same file segment. It can finish download.
* Since pointers to file segments are returned to users in FileSegmentsHolder,
* which calls complete() on destruction, removal of failed file segments is guaranteed.
*/
std::lock_guard cache_lock(cache->mutex);
size_t users_count = cache->getUseCount(*this, cache_lock);
assert(users_count >= 1);
if (users_count == 1)
{
if (downloaded_size > 0)
{
segment_range.right = segment_range.left + downloaded_size - 1;
reserved_size = downloaded_size;
download_state = State::DOWNLOADED;
}
else
cache->remove(key(), range().left, cache_lock);
}
}
}
}
LOG_TEST(&Poco::Logger::get("kssenii"), "Complete on: {} with state: {}", range().toString(), FileSegment::toString(download_state));
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}
cv.notify_all();
}
FileSegment::State FileSegment::wait()
{
std::unique_lock segment_lock(mutex);
switch (download_state)
{
case State::DOWNLOADING:
{
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LOG_TEST(&Poco::Logger::get("kssenii"), "Waiting on: {}", range().toString());
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cv.wait_for(segment_lock, std::chrono::seconds(60)); /// TODO: use value defined by setting
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break;
}
case State::DOWNLOADED:[[fallthrough]];
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case State::NO_SPACE:
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{
break;
}
default:
{
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throw Exception(ErrorCodes::FILE_CACHE_ERROR, "Trying to wait for segment with incorrect");
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}
}
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LOG_TEST(&Poco::Logger::get("kssenii"), "Waiting on: {} finished with state: {}", range().toString(), FileSegment::toString(download_state));
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return download_state;
}
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bool FileSegment::reserve(size_t size)
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{
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if (!size)
throw Exception(ErrorCodes::FILE_CACHE_ERROR, "Zero space reservation is not allowed");
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std::lock_guard segment_lock(mutex);
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if (downloaded_size == range().size())
throw Exception(ErrorCodes::FILE_CACHE_ERROR,
"Attempt to reserve space for fully downloaded file segment");
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if (downloader_id != getCallerId())
throw Exception(ErrorCodes::FILE_CACHE_ERROR, "Space can be reserved only by downloader");
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assert(reserved_size >= downloaded_size);
std::lock_guard cache_lock(cache->mutex);
/**
* It is possible to have downloaded_size < reserved_size when reserve is called
* in case previous downloader did not fully download current file_segment
* and the caller is going to continue;
*/
size_t free_space = reserved_size - downloaded_size;
size_t size_to_reserve = size - free_space;
bool reserved;
if (downloaded_size)
reserved = cache->tryReserve(size_to_reserve, cache_lock);
else
reserved = cache->set(key(), range().left, size_to_reserve, segment_lock, cache_lock);
if (reserved)
reserved_size += size;
else
download_state = State::NO_SPACE;
return reserved;
}
String LRUFileCache::dump()
{
std::lock_guard cache_lock(mutex);
WriteBufferFromOwnString result;
for (auto it = queue.begin(); it != queue.end(); ++it)
{
auto [key, offset] = *it;
auto * cell = getCell(key, offset, cache_lock);
result << (it != queue.begin() ? ", " : "") << cell->file_segment->range().toString();
result << "(state: " << cell->file_segment->state() << ")";
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}
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return result.str();
}
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String FileSegment::toString(FileSegment::State state)
{
switch (state)
{
case FileSegment::State::DOWNLOADED:
return "DOWNLOADED";
case FileSegment::State::DOWNLOADING:
return "DOWNLOADING";
case FileSegment::State::EMPTY:
return "EMPTY";
case FileSegment::State::NO_SPACE:
return "NO_SPACE";
}
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}
}