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 <Common/FileCacheSettings.h>
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#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
{
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extern const int REMOTE_FS_OBJECT_CACHE_ERROR;
extern const int LOGICAL_ERROR;
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}
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namespace
{
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String keyToStr(const IFileCache::Key & key)
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{
return getHexUIntLowercase(key);
}
}
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static bool isQueryInitialized()
{
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return CurrentThread::isInitialized() && CurrentThread::get().getQueryContext() && CurrentThread::getQueryId().size != 0;
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}
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IFileCache::IFileCache(
const String & cache_base_path_,
const FileCacheSettings & cache_settings_)
: cache_base_path(cache_base_path_)
, max_size(cache_settings_.max_size)
, max_element_size(cache_settings_.max_elements)
, max_file_segment_size(cache_settings_.max_file_segment_size)
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, enable_filesystem_query_cache_limit(cache_settings_.enable_filesystem_query_cache_limit)
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{
}
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IFileCache::Key IFileCache::hash(const String & path)
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{
return sipHash128(path.data(), path.size());
}
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String IFileCache::getPathInLocalCache(const Key & key, size_t offset)
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{
auto key_str = keyToStr(key);
return fs::path(cache_base_path) / key_str.substr(0, 3) / key_str / std::to_string(offset);
}
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String IFileCache::getPathInLocalCache(const Key & key)
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{
auto key_str = keyToStr(key);
return fs::path(cache_base_path) / key_str.substr(0, 3) / key_str;
}
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bool IFileCache::isReadOnly()
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{
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return (!isQueryInitialized());
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}
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void IFileCache::assertInitialized() const
{
if (!is_initialized)
throw Exception(ErrorCodes::REMOTE_FS_OBJECT_CACHE_ERROR, "Cache not initialized");
}
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IFileCache::QueryContextPtr IFileCache::getCurrentQueryContext(std::lock_guard<std::mutex> & cache_lock)
{
if (!isQueryInitialized())
return nullptr;
return getQueryContext(CurrentThread::getQueryId().toString(), cache_lock);
}
IFileCache::QueryContextPtr IFileCache::getQueryContext(const String & query_id, std::lock_guard<std::mutex> &)
{
auto query_iter = query_map.find(query_id);
return (query_iter == query_map.end()) ? nullptr : query_iter->second;
}
void IFileCache::removeQueryContext(const String & query_id)
{
std::lock_guard cache_lock(mutex);
auto query_iter = query_map.find(query_id);
if (query_iter == query_map.end())
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throw Exception(ErrorCodes::LOGICAL_ERROR, "Attempt to release query context that does not exist");
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query_map.erase(query_iter);
}
IFileCache::QueryContextPtr IFileCache::getOrSetQueryContext(const String & query_id, const ReadSettings & settings, std::lock_guard<std::mutex> & cache_lock)
{
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if (query_id.empty())
return nullptr;
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auto context = getQueryContext(query_id, cache_lock);
if (!context)
{
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auto query_iter = query_map.insert({query_id, std::make_shared<QueryContext>(settings.max_query_cache_size, settings.skip_download_if_exceeds_query_cache)}).first;
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context = query_iter->second;
}
return context;
}
IFileCache::QueryContextHolder IFileCache::getQueryContextHolder(const String & query_id, const ReadSettings & settings)
{
std::lock_guard cache_lock(mutex);
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/// if enable_filesystem_query_cache_limit is true, and max_query_cache_size large than zero,
/// we create context query for current query.
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if (enable_filesystem_query_cache_limit && settings.max_query_cache_size)
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{
auto context = getOrSetQueryContext(query_id, settings, cache_lock);
return QueryContextHolder(query_id, this, context);
}
else
return QueryContextHolder();
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}
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IFileCache::QueryContextHolder::QueryContextHolder(const String & query_id_, IFileCache * cache_, IFileCache::QueryContextPtr context_)
: query_id(query_id_), cache(cache_), context(context_)
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{
}
IFileCache::QueryContextHolder::~QueryContextHolder()
{
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/// If only the query_map and the current holder hold the context_query,
/// the query has been completed and the query_context is released.
if (context && context.use_count() == 2)
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cache->removeQueryContext(query_id);
}
LRUFileCache::LRUFileCache(const String & cache_base_path_, const FileCacheSettings & cache_settings_)
: IFileCache(cache_base_path_, cache_settings_)
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, max_stash_element_size(cache_settings_.max_elements)
, enable_cache_hits_threshold(cache_settings_.enable_cache_hits_threshold)
, log(&Poco::Logger::get("LRUFileCache"))
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{
}
void LRUFileCache::initialize()
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{
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std::lock_guard cache_lock(mutex);
if (!is_initialized)
{
if (fs::exists(cache_base_path))
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loadCacheInfoIntoMemory(cache_lock);
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else
fs::create_directories(cache_base_path);
is_initialized = true;
}
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}
void LRUFileCache::useCell(
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const FileSegmentCell & cell, FileSegments & result, std::lock_guard<std::mutex> & cache_lock)
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{
auto file_segment = cell.file_segment;
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if (file_segment->isDownloaded()
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&& fs::file_size(getPathInLocalCache(file_segment->key(), file_segment->offset())) == 0)
throw Exception(ErrorCodes::LOGICAL_ERROR,
"Cannot have zero size downloaded file segments. Current file segment: {}",
file_segment->range().toString());
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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.
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queue.moveToEnd(*cell.queue_iterator, cache_lock);
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}
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}
LRUFileCache::FileSegmentCell * LRUFileCache::getCell(
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const Key & key, size_t offset, std::lock_guard<std::mutex> & /* cache_lock */)
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{
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(
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const Key & key, const FileSegment::Range & range, std::lock_guard<std::mutex> & cache_lock)
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{
/// 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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auto key_path = getPathInLocalCache(key);
files.erase(key);
if (fs::exists(key_path))
fs::remove(key_path);
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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
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const auto & cell = file_segments.rbegin()->second;
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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;
}
}
return result;
}
FileSegments LRUFileCache::splitRangeIntoCells(
const Key & key, size_t offset, size_t size, FileSegment::State state, std::lock_guard<std::mutex> & cache_lock)
{
assert(size > 0);
auto current_pos = offset;
auto end_pos_non_included = offset + size;
size_t current_cell_size;
size_t remaining_size = size;
FileSegments file_segments;
while (current_pos < end_pos_non_included)
{
current_cell_size = std::min(remaining_size, max_file_segment_size);
remaining_size -= current_cell_size;
auto * cell = addCell(key, current_pos, current_cell_size, state, cache_lock);
if (cell)
file_segments.push_back(cell->file_segment);
assert(cell);
current_pos += current_cell_size;
}
assert(file_segments.empty() || offset + size - 1 == file_segments.back()->range().right);
return file_segments;
}
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void LRUFileCache::fillHolesWithEmptyFileSegments(
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FileSegments & file_segments,
const Key & key,
const FileSegment::Range & range,
bool fill_with_detached_file_segments,
std::lock_guard<std::mutex> & cache_lock)
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{
/// 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]
///
/// For each such hole create a cell with file segment state EMPTY.
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;
if (fill_with_detached_file_segments)
{
auto file_segment = std::make_shared<FileSegment>(current_pos, hole_size, key, this, FileSegment::State::EMPTY);
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{
std::lock_guard segment_lock(file_segment->mutex);
file_segment->markAsDetached(segment_lock);
}
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file_segments.insert(it, file_segment);
}
else
{
file_segments.splice(it, splitRangeIntoCells(key, current_pos, hole_size, FileSegment::State::EMPTY, cache_lock));
}
current_pos = segment_range.right + 1;
++it;
}
if (current_pos <= range.right)
{
/// ________] -- requested range
/// _____]
/// ^
/// segmentN
auto hole_size = range.right - current_pos + 1;
if (fill_with_detached_file_segments)
{
auto file_segment = std::make_shared<FileSegment>(current_pos, hole_size, key, this, FileSegment::State::EMPTY);
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{
std::lock_guard segment_lock(file_segment->mutex);
file_segment->markAsDetached(segment_lock);
}
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file_segments.insert(file_segments.end(), file_segment);
}
else
{
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file_segments.splice(
file_segments.end(), splitRangeIntoCells(key, current_pos, hole_size, FileSegment::State::EMPTY, cache_lock));
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}
}
}
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FileSegmentsHolder LRUFileCache::getOrSet(const Key & key, size_t offset, size_t size)
{
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assertInitialized();
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FileSegment::Range range(offset, offset + size - 1);
std::lock_guard cache_lock(mutex);
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#ifndef NDEBUG
assertCacheCorrectness(key, cache_lock);
#endif
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/// Get all segments which intersect with the given range.
auto file_segments = getImpl(key, range, cache_lock);
if (file_segments.empty())
{
file_segments = splitRangeIntoCells(key, offset, size, FileSegment::State::EMPTY, cache_lock);
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}
else
{
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fillHolesWithEmptyFileSegments(file_segments, key, range, false, cache_lock);
}
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assert(!file_segments.empty());
return FileSegmentsHolder(std::move(file_segments));
}
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FileSegmentsHolder LRUFileCache::get(const Key & key, size_t offset, size_t size)
{
assertInitialized();
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FileSegment::Range range(offset, offset + size - 1);
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std::lock_guard cache_lock(mutex);
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#ifndef NDEBUG
assertCacheCorrectness(key, cache_lock);
#endif
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/// Get all segments which intersect with the given range.
auto file_segments = getImpl(key, range, cache_lock);
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if (file_segments.empty())
{
auto file_segment = std::make_shared<FileSegment>(offset, size, key, this, FileSegment::State::EMPTY);
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{
std::lock_guard segment_lock(file_segment->mutex);
file_segment->markAsDetached(segment_lock);
}
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file_segments = { file_segment };
}
else
{
fillHolesWithEmptyFileSegments(file_segments, key, range, true, cache_lock);
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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,
std::lock_guard<std::mutex> & cache_lock)
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{
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/// Create a file segment cell and put it in `files` map by [key][offset].
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if (!size)
return nullptr; /// Empty files are not cached.
if (files[key].contains(offset))
throw Exception(
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ErrorCodes::LOGICAL_ERROR,
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"Cache already exists for key: `{}`, offset: {}, size: {}.\nCurrent cache structure: {}",
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keyToStr(key), offset, size, dumpStructureUnlocked(key, cache_lock));
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auto skip_or_download = [&]() -> FileSegmentPtr
{
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if (state == FileSegment::State::EMPTY && enable_cache_hits_threshold)
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{
auto record = records.find({key, offset});
if (record == records.end())
{
auto queue_iter = stash_queue.add(key, offset, 0, cache_lock);
records.insert({{key, offset}, queue_iter});
if (stash_queue.getElementsNum(cache_lock) > max_stash_element_size)
{
auto remove_queue_iter = stash_queue.begin();
records.erase({remove_queue_iter->key, remove_queue_iter->offset});
stash_queue.remove(remove_queue_iter, cache_lock);
}
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/// For segments that do not reach the download threshold, we do not download them, but directly read them
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return std::make_shared<FileSegment>(offset, size, key, this, FileSegment::State::SKIP_CACHE);
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}
else
{
auto queue_iter = record->second;
queue_iter->hits++;
stash_queue.moveToEnd(queue_iter, cache_lock);
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state = queue_iter->hits >= enable_cache_hits_threshold ? FileSegment::State::EMPTY : FileSegment::State::SKIP_CACHE;
return std::make_shared<FileSegment>(offset, size, key, this, state);
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}
}
else
return std::make_shared<FileSegment>(offset, size, key, this, state);
};
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FileSegmentCell cell(skip_or_download(), this, cache_lock);
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auto & offsets = files[key];
if (offsets.empty())
{
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auto key_path = getPathInLocalCache(key);
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if (!fs::exists(key_path))
fs::create_directories(key_path);
}
auto [it, inserted] = offsets.insert({offset, std::move(cell)});
if (!inserted)
throw Exception(
ErrorCodes::LOGICAL_ERROR,
"Failed to insert into cache key: `{}`, offset: {}, size: {}",
keyToStr(key), offset, size);
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return &(it->second);
}
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FileSegmentsHolder LRUFileCache::setDownloading(const Key & key, size_t offset, size_t size)
{
std::lock_guard cache_lock(mutex);
#ifndef NDEBUG
assertCacheCorrectness(key, cache_lock);
#endif
auto * cell = getCell(key, offset, cache_lock);
if (cell)
throw Exception(
ErrorCodes::REMOTE_FS_OBJECT_CACHE_ERROR,
"Cache cell already exists for key `{}` and offset {}",
keyToStr(key), offset);
auto file_segments = splitRangeIntoCells(key, offset, size, FileSegment::State::DOWNLOADING, cache_lock);
return FileSegmentsHolder(std::move(file_segments));
}
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bool LRUFileCache::tryReserve(const Key & key, size_t offset, size_t size, std::lock_guard<std::mutex> & cache_lock)
{
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auto query_context = enable_filesystem_query_cache_limit ? getCurrentQueryContext(cache_lock) : nullptr;
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/// If the context can be found, subsequent cache replacements are made through the Query context.
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if (query_context)
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{
auto res = tryReserveForQuery(key, offset, size, query_context, cache_lock);
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switch (res)
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{
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case ReserveResult::FITS_IN_QUERY_LIMIT_AND_RESERVATION_COMPLETED :
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{
/// When the maximum cache size of the query is reached, the cache will be
/// evicted from the history cache accessed by the current query.
return true;
}
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case ReserveResult::EXCEEDS_QUERY_LIMIT :
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{
/// The query currently does not have enough space to reserve.
/// It returns false and reads data directly from the remote fs.
return false;
}
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case ReserveResult::FITS_IN_QUERY_LIMIT_NEED_RESERVE_FROM_MAIN_LIST :
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{
/// When the maximum cache capacity of the request is not reached, the cache
/// block is evicted from the main LRU queue.
return tryReserveForMainList(key, offset, size, query_context, cache_lock);
}
}
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__builtin_unreachable();
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}
else
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{
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return tryReserveForMainList(key, offset, size, query_context, cache_lock);
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}
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}
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LRUFileCache::ReserveResult LRUFileCache::tryReserveForQuery(const Key & key, size_t offset, size_t size, QueryContextPtr query_context, std::lock_guard<std::mutex> & cache_lock)
{
/// The maximum cache capacity of the request is not reached, thus the
//// cache block is evicted from the main LRU queue by tryReserveForMainList().
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if (query_context->getCacheSize() + size <= query_context->getMaxCacheSize())
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{
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return ReserveResult::FITS_IN_QUERY_LIMIT_NEED_RESERVE_FROM_MAIN_LIST;
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}
/// When skip_download_if_exceeds_query_cache is true, there is no need
/// to evict old data, skip the cache and read directly from remote fs.
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else if (query_context->isSkipDownloadIfExceed())
{
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return ReserveResult::EXCEEDS_QUERY_LIMIT;
}
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/// The maximum cache size of the query is reached, the cache will be
/// evicted from the history cache accessed by the current query.
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else
{
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size_t removed_size = 0;
size_t queue_size = queue.getElementsNum(cache_lock);
auto * cell_for_reserve = getCell(key, offset, cache_lock);
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std::vector<IFileCache::LRUQueue::Iterator> ghost;
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std::vector<FileSegmentCell *> trash;
std::vector<FileSegmentCell *> to_evict;
auto is_overflow = [&]
{
return (max_size != 0 && queue.getTotalWeight(cache_lock) + size - removed_size > max_size)
|| (max_element_size != 0 && queue_size > max_element_size)
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|| (query_context->getCacheSize() + size - removed_size > query_context->getMaxCacheSize());
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};
/// Select the cache from the LRU queue held by query for expulsion.
for (auto iter = query_context->queue().begin(); iter != query_context->queue().end(); iter++)
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{
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if (!is_overflow())
break;
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auto * cell = getCell(iter->key, iter->offset, cache_lock);
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if (!cell)
{
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/// The cache corresponding to this record may be swapped out by
/// other queries, so it has become invalid.
ghost.push_back(iter);
removed_size += iter->size;
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}
else
{
size_t cell_size = cell->size();
assert(iter->size == cell_size);
if (cell->releasable())
{
auto & file_segment = cell->file_segment;
std::lock_guard segment_lock(file_segment->mutex);
switch (file_segment->download_state)
{
case FileSegment::State::DOWNLOADED:
{
to_evict.push_back(cell);
break;
}
default:
{
trash.push_back(cell);
break;
}
}
removed_size += cell_size;
--queue_size;
}
}
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}
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assert(trash.empty());
for (auto & cell : trash)
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{
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auto file_segment = cell->file_segment;
if (file_segment)
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{
query_context->remove(file_segment->key(), file_segment->offset(), cell->size(), cache_lock);
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std::lock_guard segment_lock(file_segment->mutex);
remove(file_segment->key(), file_segment->offset(), cache_lock, segment_lock);
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}
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}
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for (auto & iter : ghost)
query_context->remove(iter->key, iter->offset, iter->size, cache_lock);
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if (is_overflow())
{
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return ReserveResult::EXCEEDS_QUERY_LIMIT;
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}
if (cell_for_reserve)
{
auto queue_iterator = cell_for_reserve->queue_iterator;
if (queue_iterator)
queue.incrementSize(*queue_iterator, size, cache_lock);
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else
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cell_for_reserve->queue_iterator = queue.add(key, offset, size, cache_lock);
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}
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for (auto & cell : to_evict)
{
auto file_segment = cell->file_segment;
if (file_segment)
{
query_context->remove(file_segment->key(), file_segment->offset(), cell->size(), cache_lock);
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std::lock_guard<std::mutex> segment_lock(file_segment->mutex);
remove(file_segment->key(), file_segment->offset(), cache_lock, segment_lock);
}
}
query_context->reserve(key, offset, size, cache_lock);
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return ReserveResult::FITS_IN_QUERY_LIMIT_NEED_RESERVE_FROM_MAIN_LIST;
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}
}
bool LRUFileCache::tryReserveForMainList(
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const Key & key, size_t offset, size_t size, QueryContextPtr query_context, std::lock_guard<std::mutex> & cache_lock)
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{
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auto removed_size = 0;
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size_t queue_size = queue.getElementsNum(cache_lock);
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assert(queue_size <= max_element_size);
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/// Since space reservation is incremental, cache cell already exists if it's state is EMPTY.
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/// And it cache cell does not exist on startup -- as we first check for space and then add a cell.
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auto * cell_for_reserve = getCell(key, offset, cache_lock);
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/// A cell acquires a LRUQueue iterator on first successful space reservation attempt.
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/// cell_for_reserve can be nullptr here when we call tryReserve() from loadCacheInfoIntoMemory().
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if (!cell_for_reserve || !cell_for_reserve->queue_iterator)
queue_size += 1;
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auto is_overflow = [&]
{
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/// max_size == 0 means unlimited cache size, max_element_size means unlimited number of cache elements.
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return (max_size != 0 && queue.getTotalWeight(cache_lock) + size - removed_size > max_size)
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|| (max_element_size != 0 && queue_size > max_element_size);
};
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std::vector<FileSegmentCell *> to_evict;
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std::vector<FileSegmentCell *> trash;
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for (const auto & [entry_key, entry_offset, entry_size, _] : queue)
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{
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if (!is_overflow())
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break;
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auto * cell = getCell(entry_key, entry_offset, cache_lock);
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if (!cell)
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throw Exception(
ErrorCodes::REMOTE_FS_OBJECT_CACHE_ERROR,
"Cache became inconsistent. Key: {}, offset: {}",
keyToStr(key), offset);
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size_t cell_size = cell->size();
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assert(entry_size == cell_size);
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/// 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())
{
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auto & file_segment = cell->file_segment;
std::lock_guard segment_lock(file_segment->mutex);
switch (file_segment->download_state)
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{
case FileSegment::State::DOWNLOADED:
{
/// Cell will actually be removed only if
/// we managed to reserve enough space.
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to_evict.push_back(cell);
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break;
}
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default:
{
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trash.push_back(cell);
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break;
}
}
removed_size += cell_size;
--queue_size;
}
}
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/// This case is very unlikely, can happen in case of exception from
/// file_segment->complete(), which would be a logical error.
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assert(trash.empty());
for (auto & cell : trash)
{
auto file_segment = cell->file_segment;
if (file_segment)
{
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std::lock_guard segment_lock(file_segment->mutex);
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remove(file_segment->key(), file_segment->offset(), cache_lock, segment_lock);
}
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}
if (is_overflow())
return false;
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/// cache cell is nullptr on server startup because we first check for space and then add a cell.
if (cell_for_reserve)
{
/// queue_iteratir is std::nullopt here if no space has been reserved yet, a cache cell
/// acquires queue iterator on first successful space reservation attempt.
/// If queue iterator already exists, we need to update the size after each space reservation.
auto queue_iterator = cell_for_reserve->queue_iterator;
if (queue_iterator)
queue.incrementSize(*queue_iterator, size, cache_lock);
else
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cell_for_reserve->queue_iterator = queue.add(key, offset, size, cache_lock);
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}
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for (auto & cell : to_evict)
{
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auto file_segment = cell->file_segment;
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if (file_segment)
{
std::lock_guard<std::mutex> segment_lock(file_segment->mutex);
remove(file_segment->key(), file_segment->offset(), cache_lock, segment_lock);
}
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}
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if (queue.getTotalWeight(cache_lock) > (1ull << 63))
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throw Exception(ErrorCodes::LOGICAL_ERROR, "Cache became inconsistent. There must be a bug");
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if (query_context)
query_context->reserve(key, offset, size, cache_lock);
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return true;
}
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void LRUFileCache::remove(const Key & key)
{
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assertInitialized();
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std::lock_guard cache_lock(mutex);
auto it = files.find(key);
if (it == files.end())
return;
auto & offsets = it->second;
std::vector<FileSegmentCell *> to_remove;
to_remove.reserve(offsets.size());
for (auto & [offset, cell] : offsets)
to_remove.push_back(&cell);
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bool some_cells_were_skipped = false;
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for (auto & cell : to_remove)
{
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/// In ordinary case we remove data from cache when it's not used by anyone.
/// But if we have multiple replicated zero-copy tables on the same server
/// it became possible to start removing something from cache when it is used
/// by other "zero-copy" tables. That is why it's not an error.
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if (!cell->releasable())
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{
some_cells_were_skipped = true;
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continue;
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}
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auto file_segment = cell->file_segment;
if (file_segment)
{
std::lock_guard<std::mutex> segment_lock(file_segment->mutex);
remove(file_segment->key(), file_segment->offset(), cache_lock, segment_lock);
}
}
auto key_path = getPathInLocalCache(key);
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if (!some_cells_were_skipped)
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{
files.erase(key);
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if (fs::exists(key_path))
fs::remove(key_path);
}
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}
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void LRUFileCache::remove()
{
/// Try remove all cached files by cache_base_path.
/// Only releasable file segments are evicted.
std::lock_guard cache_lock(mutex);
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std::vector<FileSegment *> to_remove;
for (auto it = queue.begin(); it != queue.end();)
{
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const auto & [key, offset, size, _] = *it++;
auto * cell = getCell(key, offset, cache_lock);
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if (!cell)
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throw Exception(
ErrorCodes::LOGICAL_ERROR,
"Cache is in inconsistent state: LRU queue contains entries with no cache cell");
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if (cell->releasable())
{
auto file_segment = cell->file_segment;
if (file_segment)
{
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std::lock_guard segment_lock(file_segment->mutex);
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file_segment->detach(cache_lock, segment_lock);
remove(file_segment->key(), file_segment->offset(), cache_lock, segment_lock);
}
}
}
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/// Remove all access information.
records.clear();
stash_queue.removeAll(cache_lock);
}
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void LRUFileCache::remove(
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Key key, size_t offset,
std::lock_guard<std::mutex> & cache_lock, std::lock_guard<std::mutex> & /* segment_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);
if (!cell)
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throw Exception(ErrorCodes::LOGICAL_ERROR, "No cache cell for key: {}, offset: {}", keyToStr(key), offset);
if (cell->queue_iterator)
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{
queue.remove(*cell->queue_iterator, cache_lock);
}
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auto & offsets = files[key];
offsets.erase(offset);
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auto cache_file_path = getPathInLocalCache(key, offset);
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if (fs::exists(cache_file_path))
{
try
{
fs::remove(cache_file_path);
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if (is_initialized && offsets.empty())
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{
auto key_path = getPathInLocalCache(key);
files.erase(key);
if (fs::exists(key_path))
fs::remove(key_path);
}
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}
catch (...)
{
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throw Exception(ErrorCodes::REMOTE_FS_OBJECT_CACHE_ERROR,
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"Removal of cached file failed. Key: {}, offset: {}, path: {}, error: {}",
keyToStr(key), offset, cache_file_path, getCurrentExceptionMessage(false));
}
}
}
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void LRUFileCache::loadCacheInfoIntoMemory(std::lock_guard<std::mutex> & cache_lock)
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{
Key key;
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UInt64 offset = 0;
size_t size = 0;
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std::vector<std::pair<LRUQueue::Iterator, std::weak_ptr<FileSegment>>> queue_entries;
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/// 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)
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{
LOG_WARNING(log, "Unexpected file: ", offset_it->path().string());
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continue; /// Or just remove? Some unexpected file.
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}
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size = offset_it->file_size();
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if (!size)
{
fs::remove(offset_it->path());
continue;
}
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if (tryReserve(key, offset, size, cache_lock))
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{
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auto * cell = addCell(key, offset, size, FileSegment::State::DOWNLOADED, cache_lock);
if (cell)
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queue_entries.emplace_back(*cell->queue_iterator, cell->file_segment);
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}
else
{
LOG_WARNING(log,
"Cache capacity changed (max size: {}, available: {}), cached file `{}` does not fit in cache anymore (size: {})",
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max_size, getAvailableCacheSizeUnlocked(cache_lock), key_it->path().string(), size);
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fs::remove(offset_it->path());
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}
}
}
}
/// Shuffle cells to have random order in LRUQueue as at startup all cells have the same priority.
pcg64 generator(randomSeed());
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std::shuffle(queue_entries.begin(), queue_entries.end(), generator);
for (const auto & [it, file_segment] : queue_entries)
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{
/// Cell cache size changed and, for example, 1st file segment fits into cache
/// and 2nd file segment will fit only if first was evicted, then first will be removed and
/// cell is nullptr here.
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if (file_segment.expired())
continue;
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queue.moveToEnd(it, cache_lock);
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}
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#ifndef NDEBUG
assertCacheCorrectness(cache_lock);
#endif
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}
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void LRUFileCache::reduceSizeToDownloaded(
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const Key & key, size_t offset,
std::lock_guard<std::mutex> & cache_lock, std::lock_guard<std::mutex> & /* segment_lock */)
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{
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/**
* In case file was partially downloaded and it's download cannot be continued
* because of no space left in cache, we need to be able to cut cell's size to downloaded_size.
*/
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auto * cell = getCell(key, offset, cache_lock);
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if (!cell)
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{
throw Exception(
ErrorCodes::LOGICAL_ERROR,
"No cell found for key: {}, offset: {}",
keyToStr(key), offset);
}
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const auto & file_segment = cell->file_segment;
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size_t downloaded_size = file_segment->downloaded_size;
if (downloaded_size == file_segment->range().size())
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{
throw Exception(
ErrorCodes::LOGICAL_ERROR,
"Nothing to reduce, file segment fully downloaded, key: {}, offset: {}",
keyToStr(key), offset);
}
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cell->file_segment = std::make_shared<FileSegment>(offset, downloaded_size, key, this, FileSegment::State::DOWNLOADED);
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}
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bool LRUFileCache::isLastFileSegmentHolder(
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const Key & key, size_t offset,
std::lock_guard<std::mutex> & cache_lock, std::lock_guard<std::mutex> & /* segment_lock */)
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{
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auto * cell = getCell(key, offset, cache_lock);
if (!cell)
throw Exception(ErrorCodes::LOGICAL_ERROR, "No cell found for key: {}, offset: {}", keyToStr(key), offset);
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/// The caller of this method is last file segment holder if use count is 2 (the second pointer is cache itself)
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return cell->file_segment.use_count() == 2;
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}
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FileSegments LRUFileCache::getSnapshot() const
{
std::lock_guard cache_lock(mutex);
FileSegments file_segments;
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for (const auto & [key, cells_by_offset] : files)
{
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for (const auto & [offset, cell] : cells_by_offset)
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file_segments.push_back(FileSegment::getSnapshot(cell.file_segment, cache_lock));
}
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return file_segments;
}
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std::vector<String> LRUFileCache::tryGetCachePaths(const Key & key)
{
std::lock_guard cache_lock(mutex);
std::vector<String> cache_paths;
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const auto & cells_by_offset = files[key];
for (const auto & [offset, cell] : cells_by_offset)
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{
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if (cell.file_segment->state() == FileSegment::State::DOWNLOADED)
cache_paths.push_back(getPathInLocalCache(key, offset));
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}
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return cache_paths;
}
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size_t LRUFileCache::getUsedCacheSize() const
{
std::lock_guard cache_lock(mutex);
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return getUsedCacheSizeUnlocked(cache_lock);
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}
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size_t LRUFileCache::getUsedCacheSizeUnlocked(std::lock_guard<std::mutex> & cache_lock) const
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{
return queue.getTotalWeight(cache_lock);
}
size_t LRUFileCache::getAvailableCacheSize() const
{
std::lock_guard cache_lock(mutex);
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return getAvailableCacheSizeUnlocked(cache_lock);
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}
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size_t LRUFileCache::getAvailableCacheSizeUnlocked(std::lock_guard<std::mutex> & cache_lock) const
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{
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return max_size - getUsedCacheSizeUnlocked(cache_lock);
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}
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size_t LRUFileCache::getFileSegmentsNum() const
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{
std::lock_guard cache_lock(mutex);
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return getFileSegmentsNumUnlocked(cache_lock);
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}
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size_t LRUFileCache::getFileSegmentsNumUnlocked(std::lock_guard<std::mutex> & cache_lock) const
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{
return queue.getElementsNum(cache_lock);
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}
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LRUFileCache::FileSegmentCell::FileSegmentCell(
FileSegmentPtr file_segment_,
LRUFileCache * cache,
std::lock_guard<std::mutex> & cache_lock)
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: file_segment(file_segment_)
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{
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/**
* Cell can be created with either DOWNLOADED or EMPTY file segment's state.
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* File segment acquires DOWNLOADING state and creates LRUQueue iterator on first
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* successful getOrSetDownaloder call.
*/
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switch (file_segment->download_state)
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{
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case FileSegment::State::DOWNLOADED:
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{
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queue_iterator = cache->queue.add(file_segment->key(), file_segment->offset(), file_segment->range().size(), cache_lock);
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break;
}
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case FileSegment::State::SKIP_CACHE:
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case FileSegment::State::EMPTY:
case FileSegment::State::DOWNLOADING:
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{
break;
}
default:
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throw Exception(ErrorCodes::REMOTE_FS_OBJECT_CACHE_ERROR,
"Can create cell with either EMPTY, DOWNLOADED, DOWNLOADING state, got: {}",
FileSegment::stateToString(file_segment->download_state));
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}
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}
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IFileCache::LRUQueue::Iterator IFileCache::LRUQueue::add(
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const IFileCache::Key & key, size_t offset, size_t size, std::lock_guard<std::mutex> & /* cache_lock */)
{
#ifndef NDEBUG
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for (const auto & [entry_key, entry_offset, entry_size, entry_hits] : queue)
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{
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if (entry_key == key && entry_offset == offset)
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throw Exception(
ErrorCodes::LOGICAL_ERROR,
"Attempt to add duplicate queue entry to queue. (Key: {}, offset: {}, size: {})",
keyToStr(key), offset, size);
}
#endif
cache_size += size;
return queue.insert(queue.end(), FileKeyAndOffset(key, offset, size));
}
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void IFileCache::LRUQueue::remove(Iterator queue_it, std::lock_guard<std::mutex> & /* cache_lock */)
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{
cache_size -= queue_it->size;
queue.erase(queue_it);
}
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void IFileCache::LRUQueue::removeAll(std::lock_guard<std::mutex> & /* cache_lock */)
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{
queue.clear();
cache_size = 0;
}
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void IFileCache::LRUQueue::moveToEnd(Iterator queue_it, std::lock_guard<std::mutex> & /* cache_lock */)
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{
queue.splice(queue.end(), queue, queue_it);
}
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void IFileCache::LRUQueue::incrementSize(Iterator queue_it, size_t size_increment, std::lock_guard<std::mutex> & /* cache_lock */)
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{
cache_size += size_increment;
queue_it->size += size_increment;
}
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bool IFileCache::LRUQueue::contains(
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const IFileCache::Key & key, size_t offset, std::lock_guard<std::mutex> & /* cache_lock */) const
{
/// This method is used for assertions in debug mode.
/// So we do not care about complexity here.
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for (const auto & [entry_key, entry_offset, size, _] : queue)
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{
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if (key == entry_key && offset == entry_offset)
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return true;
}
return false;
}
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String IFileCache::LRUQueue::toString(std::lock_guard<std::mutex> & /* cache_lock */) const
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{
String result;
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for (const auto & [key, offset, size, _] : queue)
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{
if (!result.empty())
result += ", ";
result += fmt::format("{}: [{}, {}]", keyToStr(key), offset, offset + size - 1);
}
return result;
}
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String LRUFileCache::dumpStructure(const Key & key)
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{
std::lock_guard cache_lock(mutex);
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return dumpStructureUnlocked(key, cache_lock);
}
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String LRUFileCache::dumpStructureUnlocked(const Key & key, std::lock_guard<std::mutex> & cache_lock)
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{
WriteBufferFromOwnString result;
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const auto & cells_by_offset = files[key];
for (const auto & [offset, cell] : cells_by_offset)
result << cell.file_segment->getInfoForLog() << "\n";
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result << "\n\nQueue: " << queue.toString(cache_lock);
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return result.str();
}
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void LRUFileCache::assertCacheCellsCorrectness(
const FileSegmentsByOffset & cells_by_offset, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
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{
for (const auto & [_, cell] : cells_by_offset)
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{
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const auto & file_segment = cell.file_segment;
file_segment->assertCorrectness();
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if (file_segment->reserved_size != 0)
{
assert(cell.queue_iterator);
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assert(queue.contains(file_segment->key(), file_segment->offset(), cache_lock));
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}
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}
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}
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void LRUFileCache::assertCacheCorrectness(const Key & key, std::lock_guard<std::mutex> & cache_lock)
{
assertCacheCellsCorrectness(files[key], cache_lock);
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assertQueueCorrectness(cache_lock);
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}
void LRUFileCache::assertCacheCorrectness(std::lock_guard<std::mutex> & cache_lock)
{
for (const auto & [key, cells_by_offset] : files)
assertCacheCellsCorrectness(files[key], cache_lock);
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assertQueueCorrectness(cache_lock);
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}
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void LRUFileCache::assertQueueCorrectness(std::lock_guard<std::mutex> & cache_lock)
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{
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[[maybe_unused]] size_t total_size = 0;
for (auto it = queue.begin(); it != queue.end();)
{
auto & [key, offset, size, _] = *it++;
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auto * cell = getCell(key, offset, cache_lock);
if (!cell)
{
throw Exception(
ErrorCodes::LOGICAL_ERROR,
"Cache is in inconsistent state: LRU queue contains entries with no cache cell (assertCorrectness())");
}
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assert(cell->size() == size);
total_size += size;
}
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assert(total_size == queue.getTotalWeight(cache_lock));
assert(queue.getTotalWeight(cache_lock) <= max_size);
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assert(queue.getElementsNum(cache_lock) <= max_element_size);
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}
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}