ClickHouse/dbms/Common/ArrayCache.h

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#pragma once
#include <atomic>
#include <mutex>
#include <list>
#include <memory>
#include <random>
#include <pcg_random.hpp>
#include <unordered_map>
#include <sys/mman.h>
#include <boost/intrusive/list.hpp>
#include <boost/intrusive/set.hpp>
#include <boost/noncopyable.hpp>
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#include <ext/scope_guard.h>
#include <Common/Exception.h>
#include <Common/randomSeed.h>
#include <Common/formatReadable.h>
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/// Required for older Darwin builds, that lack definition of MAP_ANONYMOUS
#ifndef MAP_ANONYMOUS
#define MAP_ANONYMOUS MAP_ANON
#endif
namespace DB
{
namespace ErrorCodes
{
extern const int CANNOT_ALLOCATE_MEMORY;
extern const int CANNOT_MUNMAP;
}
}
/** Cache for variable length memory regions (contiguous arrays of bytes).
* Example: cache for data read from disk, cache for decompressed data, etc.
* It combines cache and allocator: allocates memory by itself without use of malloc/new.
*
* Motivation:
* - cache has specified memory usage limit and we want this limit to include allocator fragmentation overhead;
* - the cache overcomes memory fragmentation by cache eviction;
* - there is no sense for reclaimed memory regions to be cached internally by usual allocator (malloc/new);
* - by allocating memory directly with mmap, we could place it in virtual address space far
* from other (malloc'd) memory - this helps debugging memory stomping bugs
* (your program will likely hit unmapped memory and get segfault rather than silent cache corruption)
*
* Implementation:
*
* Cache is represented by list of mmapped chunks.
* Each chunk holds free and occupied memory regions. Contiguous free regions are always coalesced.
*
* Each region could be linked by following metadata structures:
* 1. LRU list - to find next region for eviction. NOTE Replace with exponentially-smoothed size-weighted LFU map.
* 2. Adjacency list - to find neighbour free regions to coalesce on eviction.
* 3. Size multimap - to find free region with at least requested size.
* 4. Key map - to find element by key.
*
* Each region has:
* - size;
* - refcount: region could be evicted only if it is not used anywhere;
* - chunk address: to check if regions are from same chunk.
*
* During insertion, each key is locked - to avoid parallel initialization of regions for same key.
*
* On insertion, we search for free region of at least requested size.
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* If nothing was found, we evict oldest unused region; if not enough size, we evict it neighbours; and try again.
*
* Metadata is allocated by usual allocator and its memory usage is not accounted.
*
* Caveats:
* - cache is not NUMA friendly.
*
* Performance: few million ops/sec from single thread, less in case of concurrency.
* Fragmentation is usually less than 10%.
*/
template <typename Key, typename Payload>
class ArrayCache : private boost::noncopyable
{
private:
struct LRUListTag;
struct AdjacencyListTag;
struct SizeMultimapTag;
struct KeyMapTag;
using LRUListHook = boost::intrusive::list_base_hook<boost::intrusive::tag<LRUListTag>>;
using AdjacencyListHook = boost::intrusive::list_base_hook<boost::intrusive::tag<AdjacencyListTag>>;
using SizeMultimapHook = boost::intrusive::set_base_hook<boost::intrusive::tag<SizeMultimapTag>>;
using KeyMapHook = boost::intrusive::set_base_hook<boost::intrusive::tag<KeyMapTag>>;
struct RegionMetadata : public LRUListHook, AdjacencyListHook, SizeMultimapHook, KeyMapHook
{
Key key;
Payload payload;
union
{
void * ptr;
char * char_ptr;
};
size_t size;
size_t refcount = 0;
void * chunk;
bool operator< (const RegionMetadata & other) const { return size < other.size; }
bool isFree() const { return SizeMultimapHook::is_linked(); }
static RegionMetadata * create()
{
return new RegionMetadata;
}
void destroy()
{
delete this;
}
private:
RegionMetadata() = default;
~RegionMetadata() = default;
};
struct RegionCompareBySize
{
bool operator() (const RegionMetadata & a, const RegionMetadata & b) const { return a.size < b.size; }
bool operator() (const RegionMetadata & a, size_t size) const { return a.size < size; }
bool operator() (size_t size, const RegionMetadata & b) const { return size < b.size; }
};
struct RegionCompareByKey
{
bool operator() (const RegionMetadata & a, const RegionMetadata & b) const { return a.key < b.key; }
bool operator() (const RegionMetadata & a, Key key) const { return a.key < key; }
bool operator() (Key key, const RegionMetadata & b) const { return key < b.key; }
};
using LRUList = boost::intrusive::list<RegionMetadata,
boost::intrusive::base_hook<LRUListHook>, boost::intrusive::constant_time_size<true>>;
using AdjacencyList = boost::intrusive::list<RegionMetadata,
boost::intrusive::base_hook<AdjacencyListHook>, boost::intrusive::constant_time_size<true>>;
using SizeMultimap = boost::intrusive::multiset<RegionMetadata,
boost::intrusive::compare<RegionCompareBySize>, boost::intrusive::base_hook<SizeMultimapHook>, boost::intrusive::constant_time_size<true>>;
using KeyMap = boost::intrusive::set<RegionMetadata,
boost::intrusive::compare<RegionCompareByKey>, boost::intrusive::base_hook<KeyMapHook>, boost::intrusive::constant_time_size<true>>;
/** Each region could be:
* - free: not holding any data;
* - allocated: having data, addressed by key;
* -- allocated, in use: holded externally, could not be evicted;
* -- allocated, not in use: not holded, could be evicted.
*/
/** Invariants:
* adjacency_list contains all regions
* size_multimap contains free regions
* key_map contains allocated regions
* lru_list contains allocated regions, that are not in use
*/
LRUList lru_list;
AdjacencyList adjacency_list;
SizeMultimap size_multimap;
KeyMap key_map;
mutable std::mutex mutex;
pcg64 rng{randomSeed()};
struct Chunk : private boost::noncopyable
{
void * ptr;
size_t size;
Chunk(size_t size_, void * address_hint) : size(size_)
{
ptr = mmap(address_hint, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (MAP_FAILED == ptr)
DB::throwFromErrno("Allocator: Cannot mmap " + formatReadableSizeWithBinarySuffix(size) + ".", DB::ErrorCodes::CANNOT_ALLOCATE_MEMORY);
}
~Chunk()
{
if (ptr && 0 != munmap(ptr, size))
DB::throwFromErrno("Allocator: Cannot munmap " + formatReadableSizeWithBinarySuffix(size) + ".", DB::ErrorCodes::CANNOT_MUNMAP);
}
Chunk(Chunk && other) : ptr(other.ptr), size(other.size)
{
other.ptr = nullptr;
}
};
using Chunks = std::list<Chunk>;
Chunks chunks;
size_t total_chunks_size = 0;
size_t total_allocated_size = 0;
std::atomic<size_t> total_size_currently_initialized {0};
size_t total_size_in_use = 0;
/// Max size of cache.
const size_t max_total_size;
/// We will allocate memory in chunks of at least that size.
/// 64 MB makes mmap overhead comparable to memory throughput.
static constexpr size_t min_chunk_size = 64 * 1024 * 1024;
/// Cache stats.
std::atomic<size_t> hits {0}; /// Value was in cache.
std::atomic<size_t> concurrent_hits {0}; /// Value was calculated by another thread and we was waiting for it. Also summed in hits.
std::atomic<size_t> misses {0};
/// For whole lifetime.
size_t allocations = 0;
size_t allocated_bytes = 0;
size_t evictions = 0;
size_t evicted_bytes = 0;
size_t secondary_evictions = 0;
public:
/// Holds region as in use. Regions in use could not be evicted from cache.
/// In constructor, increases refcount and if it becomes non-zero, remove region from lru_list.
/// In destructor, decreases refcount and if it becomes zero, insert region to lru_list.
struct Holder : private boost::noncopyable
{
Holder(ArrayCache & cache_, RegionMetadata & region_) : cache(cache_), region(region_)
{
if (++region.refcount == 1 && region.LRUListHook::is_linked())
cache.lru_list.erase(cache.lru_list.iterator_to(region));
cache.total_size_in_use += region.size;
}
~Holder()
{
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std::lock_guard cache_lock(cache.mutex);
if (--region.refcount == 0)
cache.lru_list.push_back(region);
cache.total_size_in_use -= region.size;
}
void * ptr() { return region.ptr; }
const void * ptr() const { return region.ptr; }
size_t size() const { return region.size; }
Key key() const { return region.key; }
Payload & payload() { return region.payload; }
const Payload & payload() const { return region.payload; }
private:
ArrayCache & cache;
RegionMetadata & region;
};
using HolderPtr = std::shared_ptr<Holder>;
private:
/// Represents pending insertion attempt.
struct InsertToken
{
InsertToken(ArrayCache & cache_) : cache(cache_) {}
std::mutex mutex;
bool cleaned_up = false; /// Protected by the token mutex
HolderPtr value; /// Protected by the token mutex
ArrayCache & cache;
size_t refcount = 0; /// Protected by the cache mutex
};
using InsertTokens = std::unordered_map<Key, std::shared_ptr<InsertToken>>;
InsertTokens insert_tokens;
/// This class is responsible for removing used insert tokens from the insert_tokens map.
/// Among several concurrent threads the first successful one is responsible for removal. But if they all
/// fail, then the last one is responsible.
struct InsertTokenHolder
{
const Key * key = nullptr;
std::shared_ptr<InsertToken> token;
bool cleaned_up = false;
InsertTokenHolder() = default;
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void acquire(const Key * key_, const std::shared_ptr<InsertToken> & token_, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
key = key_;
token = token_;
++token->refcount;
}
void cleanup([[maybe_unused]] std::lock_guard<std::mutex> & token_lock, [[maybe_unused]] std::lock_guard<std::mutex> & cache_lock)
{
token->cache.insert_tokens.erase(*key);
token->cleaned_up = true;
cleaned_up = true;
}
~InsertTokenHolder()
{
if (!token)
return;
if (cleaned_up)
return;
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std::lock_guard token_lock(token->mutex);
if (token->cleaned_up)
return;
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std::lock_guard cache_lock(token->cache.mutex);
--token->refcount;
if (token->refcount == 0)
cleanup(token_lock, cache_lock);
}
};
friend struct InsertTokenHolder;
static size_t roundUp(size_t x, size_t rounding)
{
return (x + (rounding - 1)) / rounding * rounding;
}
static constexpr size_t page_size = 4096;
/// Sizes and addresses of allocated memory will be aligned to specified boundary.
static constexpr size_t alignment = 16;
/// Precondition: region is not in lru_list, not in key_map, not in size_multimap.
/// Postcondition: region is not in lru_list, not in key_map,
/// inserted into size_multimap, possibly coalesced with adjacent free regions.
void freeRegion(RegionMetadata & region) noexcept
{
auto adjacency_list_it = adjacency_list.iterator_to(region);
auto left_it = adjacency_list_it;
auto right_it = adjacency_list_it;
//size_t was_size = region.size;
if (left_it != adjacency_list.begin())
{
--left_it;
//std::cerr << "left_it->isFree(): " << left_it->isFree() << "\n";
if (left_it->chunk == region.chunk && left_it->isFree())
{
region.size += left_it->size;
region.char_ptr-= left_it->size;
size_multimap.erase(size_multimap.iterator_to(*left_it));
adjacency_list.erase_and_dispose(left_it, [](RegionMetadata * elem) { elem->destroy(); });
}
}
++right_it;
if (right_it != adjacency_list.end())
{
//std::cerr << "right_it->isFree(): " << right_it->isFree() << "\n";
if (right_it->chunk == region.chunk && right_it->isFree())
{
region.size += right_it->size;
size_multimap.erase(size_multimap.iterator_to(*right_it));
adjacency_list.erase_and_dispose(right_it, [](RegionMetadata * elem) { elem->destroy(); });
}
}
//std::cerr << "size is enlarged: " << was_size << " -> " << region.size << "\n";
size_multimap.insert(region);
}
void evictRegion(RegionMetadata & evicted_region) noexcept
{
total_allocated_size -= evicted_region.size;
lru_list.erase(lru_list.iterator_to(evicted_region));
if (evicted_region.KeyMapHook::is_linked())
key_map.erase(key_map.iterator_to(evicted_region));
++evictions;
evicted_bytes += evicted_region.size;
freeRegion(evicted_region);
}
/// Evict region from cache and return it, coalesced with nearby free regions.
/// While size is not enough, evict adjacent regions at right, if any.
/// If nothing to evict, returns nullptr.
/// Region is removed from lru_list and key_map and inserted into size_multimap.
RegionMetadata * evictSome(size_t requested_size) noexcept
{
if (lru_list.empty())
return nullptr;
/*for (const auto & elem : adjacency_list)
std::cerr << (!elem.SizeMultimapHook::is_linked() ? "\033[1m" : "") << elem.size << (!elem.SizeMultimapHook::is_linked() ? "\033[0m " : " ");
std::cerr << '\n';*/
auto it = adjacency_list.iterator_to(lru_list.front());
while (true)
{
RegionMetadata & evicted_region = *it;
evictRegion(evicted_region);
if (evicted_region.size >= requested_size)
return &evicted_region;
++it;
if (it == adjacency_list.end() || it->chunk != evicted_region.chunk || !it->LRUListHook::is_linked())
return &evicted_region;
++secondary_evictions;
}
}
/// Allocates a chunk of specified size. Creates free region, spanning through whole chunk and returns it.
RegionMetadata * addNewChunk(size_t size)
{
/// ASLR by hand.
void * address_hint = reinterpret_cast<void *>(std::uniform_int_distribution<size_t>(0x100000000000UL, 0x700000000000UL)(rng));
chunks.emplace_back(size, address_hint);
Chunk & chunk = chunks.back();
total_chunks_size += size;
/// Create free region spanning through chunk.
RegionMetadata * free_region;
try
{
free_region = RegionMetadata::create();
}
catch (...)
{
total_chunks_size -= size;
chunks.pop_back();
throw;
}
free_region->ptr = chunk.ptr;
free_region->chunk = chunk.ptr;
free_region->size = chunk.size;
adjacency_list.push_back(*free_region);
size_multimap.insert(*free_region);
return free_region;
}
/// Precondition: free_region.size >= size.
RegionMetadata * allocateFromFreeRegion(RegionMetadata & free_region, size_t size)
{
++allocations;
allocated_bytes += size;
if (free_region.size == size)
{
total_allocated_size += size;
size_multimap.erase(size_multimap.iterator_to(free_region));
return &free_region;
}
RegionMetadata * allocated_region = RegionMetadata::create();
total_allocated_size += size;
allocated_region->ptr = free_region.ptr;
allocated_region->chunk = free_region.chunk;
allocated_region->size = size;
size_multimap.erase(size_multimap.iterator_to(free_region));
free_region.size -= size;
free_region.char_ptr += size;
size_multimap.insert(free_region);
adjacency_list.insert(adjacency_list.iterator_to(free_region), *allocated_region);
return allocated_region;
}
/// Does not insert allocated region to key_map or lru_list. Caller must do it.
RegionMetadata * allocate(size_t size)
{
size = roundUp(size, alignment);
/// Look up to size multimap to find free region of specified size.
auto it = size_multimap.lower_bound(size, RegionCompareBySize());
if (size_multimap.end() != it)
{
return allocateFromFreeRegion(*it, size);
}
/// If nothing was found and total size of allocated chunks plus required size is lower than maximum,
/// allocate a new chunk.
size_t required_chunk_size = std::max(min_chunk_size, roundUp(size, page_size));
if (total_chunks_size + required_chunk_size <= max_total_size)
{
/// Create free region spanning through chunk.
RegionMetadata * free_region = addNewChunk(required_chunk_size);
return allocateFromFreeRegion(*free_region, size);
}
// std::cerr << "Requested size: " << size << "\n";
/// Evict something from cache and continue.
while (true)
{
RegionMetadata * res = evictSome(size);
/// Nothing to evict. All cache is full and in use - cannot allocate memory.
if (!res)
return nullptr;
/// Not enough. Evict more.
if (res->size < size)
continue;
return allocateFromFreeRegion(*res, size);
}
}
public:
ArrayCache(size_t max_total_size_) : max_total_size(max_total_size_)
{
}
~ArrayCache()
{
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std::lock_guard cache_lock(mutex);
key_map.clear();
lru_list.clear();
size_multimap.clear();
adjacency_list.clear_and_dispose([](RegionMetadata * elem) { elem->destroy(); });
}
/// If the value for the key is in the cache, returns it.
///
/// If it is not, calls 'get_size' to obtain required size of storage for key,
/// then allocates storage and call 'initialize' for necessary initialization before data from cache could be used.
///
/// Only one of several concurrent threads calling this method will call get_size or initialize,
/// others will wait for that call to complete and will use its result (this helps prevent cache stampede).
///
/// Exceptions occuring in callbacks will be propagated to the caller.
/// Another thread from the set of concurrent threads will then try to call its callbacks etc.
///
/// Returns cached value wrapped by holder, preventing cache entry from eviction.
/// Also could return a bool indicating whether the value was produced during this call.
template <typename GetSizeFunc, typename InitializeFunc>
HolderPtr getOrSet(const Key & key, GetSizeFunc && get_size, InitializeFunc && initialize, bool * was_calculated)
{
InsertTokenHolder token_holder;
{
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std::lock_guard cache_lock(mutex);
auto it = key_map.find(key, RegionCompareByKey());
if (key_map.end() != it)
{
++hits;
if (was_calculated)
*was_calculated = false;
return std::make_shared<Holder>(*this, *it);
}
auto & token = insert_tokens[key];
if (!token)
token = std::make_shared<InsertToken>(*this);
token_holder.acquire(&key, token, cache_lock);
}
InsertToken * token = token_holder.token.get();
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std::lock_guard token_lock(token->mutex);
token_holder.cleaned_up = token->cleaned_up;
if (token->value)
{
/// Another thread already produced the value while we waited for token->mutex.
++hits;
++concurrent_hits;
if (was_calculated)
*was_calculated = false;
return token->value;
}
++misses;
size_t size = get_size();
RegionMetadata * region;
{
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std::lock_guard cache_lock(mutex);
region = allocate(size);
}
/// Cannot allocate memory.
if (!region)
return {};
region->key = key;
{
total_size_currently_initialized += size;
SCOPE_EXIT({ total_size_currently_initialized -= size; });
try
{
initialize(region->ptr, region->payload);
}
catch (...)
{
{
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std::lock_guard cache_lock(mutex);
freeRegion(*region);
}
throw;
}
}
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std::lock_guard cache_lock(mutex);
try
{
token->value = std::make_shared<Holder>(*this, *region);
/// Insert the new value only if the token is still in present in insert_tokens.
/// (The token may be absent because of a concurrent reset() call).
auto token_it = insert_tokens.find(key);
if (token_it != insert_tokens.end() && token_it->second.get() == token)
{
key_map.insert(*region);
}
if (!token->cleaned_up)
token_holder.cleanup(token_lock, cache_lock);
if (was_calculated)
*was_calculated = true;
return token->value;
}
catch (...)
{
if (region->KeyMapHook::is_linked())
key_map.erase(key_map.iterator_to(*region));
freeRegion(*region);
throw;
}
}
struct Statistics
{
size_t total_chunks_size = 0;
size_t total_allocated_size = 0;
size_t total_size_currently_initialized = 0;
size_t total_size_in_use = 0;
size_t num_chunks = 0;
size_t num_regions = 0;
size_t num_free_regions = 0;
size_t num_regions_in_use = 0;
size_t num_keyed_regions = 0;
size_t hits = 0;
size_t concurrent_hits = 0;
size_t misses = 0;
size_t allocations = 0;
size_t allocated_bytes = 0;
size_t evictions = 0;
size_t evicted_bytes = 0;
size_t secondary_evictions = 0;
};
Statistics getStatistics() const
{
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std::lock_guard cache_lock(mutex);
Statistics res;
res.total_chunks_size = total_chunks_size;
res.total_allocated_size = total_allocated_size;
res.total_size_currently_initialized = total_size_currently_initialized.load(std::memory_order_relaxed);
res.total_size_in_use = total_size_in_use;
res.num_chunks = chunks.size();
res.num_regions = adjacency_list.size();
res.num_free_regions = size_multimap.size();
res.num_regions_in_use = adjacency_list.size() - size_multimap.size() - lru_list.size();
res.num_keyed_regions = key_map.size();
res.hits = hits.load(std::memory_order_relaxed);
res.concurrent_hits = concurrent_hits.load(std::memory_order_relaxed);
res.misses = misses.load(std::memory_order_relaxed);
res.allocations = allocations;
res.allocated_bytes = allocated_bytes;
res.evictions = evictions;
res.evicted_bytes = evicted_bytes;
res.secondary_evictions = secondary_evictions;
return res;
}
};
template <typename Key, typename Payload> constexpr size_t ArrayCache<Key, Payload>::min_chunk_size;