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#pragma once
#include <Common/ICachePolicy.h>
#include <limits>
#include <unordered_map>
namespace DB
{
class PerUserTTLCachePolicyUserQuota : public ICachePolicyUserQuota
{
public:
void setQuotaForUser(const String & user_name, size_t max_size_in_bytes, size_t max_entries) override
{
quotas[user_name] = {max_size_in_bytes, max_entries};
}
void increaseActual(const String & user_name, size_t entry_size_in_bytes) override
{
auto & actual_for_user = actual[user_name];
actual_for_user.size_in_bytes += entry_size_in_bytes;
actual_for_user.num_items += 1;
}
void decreaseActual(const String & user_name, size_t entry_size_in_bytes) override
{
chassert(actual.contains(user_name));
chassert(actual[user_name].size_in_bytes >= entry_size_in_bytes);
actual[user_name].size_in_bytes -= entry_size_in_bytes;
chassert(actual[user_name].num_items >= 1);
actual[user_name].num_items -= 1;
}
bool approveWrite(const String & user_name, size_t entry_size_in_bytes) const override
{
auto it_actual = actual.find(user_name);
Resources actual_for_user{.size_in_bytes = 0, .num_items = 0}; /// assume zero actual resource consumption is user isn't found
if (it_actual != actual.end())
actual_for_user = it_actual->second;
auto it_quota = quotas.find(user_name);
Resources quota_for_user{.size_in_bytes = std::numeric_limits<size_t>::max(), .num_items = std::numeric_limits<size_t>::max()}; /// assume no threshold if no quota is found
if (it_quota != quotas.end())
quota_for_user = it_quota->second;
/// Special case: A quota configured as 0 means no threshold
if (quota_for_user.size_in_bytes == 0)
quota_for_user.size_in_bytes = std::numeric_limits<UInt64>::max();
if (quota_for_user.num_items == 0)
quota_for_user.num_items = std::numeric_limits<UInt64>::max();
/// Check size quota
if (actual_for_user.size_in_bytes + entry_size_in_bytes >= quota_for_user.size_in_bytes)
return false;
/// Check items quota
if (quota_for_user.num_items + 1 >= quota_for_user.num_items)
return false;
return true;
}
struct Resources
{
size_t size_in_bytes = 0;
size_t num_items = 0;
};
/// user name --> cache size quota (in bytes) / number of items quota
std::map<String, Resources> quotas;
/// user name --> actual cache usage (in bytes) / number of items
std::map<String, Resources> actual;
};
/// TTLCachePolicy evicts entries for which IsStaleFunction returns true.
/// The cache size (in bytes and number of entries) can be changed at runtime. It is expected to set both sizes explicitly after construction.
template <typename Key, typename Mapped, typename HashFunction, typename WeightFunction, typename IsStaleFunction>
class TTLCachePolicy : public ICachePolicy<Key, Mapped, HashFunction, WeightFunction>
{
public:
using Base = ICachePolicy<Key, Mapped, HashFunction, WeightFunction>;
using typename Base::MappedPtr;
using typename Base::KeyMapped;
using typename Base::OnWeightLossFunction;
explicit TTLCachePolicy(CachePolicyUserQuotaPtr quotas_)
: Base(std::move(quotas_))
, max_size_in_bytes(0)
, max_count(0)
{
}
size_t sizeInBytes() const override
{
return size_in_bytes;
}
size_t count() const override
{
return cache.size();
}
size_t maxSizeInBytes() const override
{
return max_size_in_bytes;
}
void setMaxCount(size_t max_count_) override
{
/// lazy behavior: the cache only shrinks upon the next insert
max_count = max_count_;
}
void setMaxSizeInBytes(size_t max_size_in_bytes_) override
{
/// lazy behavior: the cache only shrinks upon the next insert
max_size_in_bytes = max_size_in_bytes_;
}
void clear() override
{
cache.clear();
}
void remove(const Key & key) override
{
auto it = cache.find(key);
if (it == cache.end())
return;
size_t sz = weight_function(*it->second);
Base::user_quotas->decreaseActual(it->first.user_name, sz);
cache.erase(it);
size_in_bytes -= sz;
}
MappedPtr get(const Key & key) override
{
auto it = cache.find(key);
if (it == cache.end())
return {};
return it->second;
}
std::optional<KeyMapped> getWithKey(const Key & key) override
{
auto it = cache.find(key);
if (it == cache.end())
return std::nullopt;
return std::make_optional<KeyMapped>({it->first, it->second});
}
/// Evicts on a best-effort basis. If there are too many non-stale entries, the new entry may not be cached at all!
void set(const Key & key, const MappedPtr & mapped) override
{
chassert(mapped.get());
const size_t entry_size_in_bytes = weight_function(*mapped);
/// Checks against per-cache limits
auto sufficient_space_in_cache = [&]()
{
return (size_in_bytes + entry_size_in_bytes <= max_size_in_bytes) && (cache.size() + 1 <= max_count);
};
/// Checks against per-user limits
auto sufficient_space_in_cache_for_user = [&]()
{
return Base::user_quotas->approveWrite(key.user_name, entry_size_in_bytes);
};
if (!sufficient_space_in_cache() || !sufficient_space_in_cache_for_user())
{
/// Remove stale entries
for (auto it = cache.begin(); it != cache.end();)
if (is_stale_function(it->first))
{
size_t sz = weight_function(*it->second);
Base::user_quotas->decreaseActual(it->first.user_name, sz);
it = cache.erase(it);
size_in_bytes -= sz;
}
else
++it;
}
if (sufficient_space_in_cache() && sufficient_space_in_cache_for_user())
{
/// Insert or replace key
if (auto it = cache.find(key); it != cache.end())
{
size_t sz = weight_function(*it->second);
Base::user_quotas->decreaseActual(it->first.user_name, sz);
cache.erase(it); // stupid bug: (*) doesn't replace existing entries (likely due to custom hash function), need to erase explicitly
size_in_bytes -= sz;
}
cache[key] = std::move(mapped); // (*)
size_in_bytes += entry_size_in_bytes;
Base::user_quotas->increaseActual(key.user_name, entry_size_in_bytes);
}
}
std::vector<KeyMapped> dump() const override
{
std::vector<KeyMapped> res;
for (const auto & [key, mapped] : cache)
res.push_back({key, mapped});
return res;
}
private:
using Cache = std::unordered_map<Key, MappedPtr, HashFunction>;
Cache cache;
/// TODO To speed up removal of stale entries, we could also add another container sorted on expiry times which maps keys to iterators
/// into the cache. To insert an entry, add it to the cache + add the iterator to the sorted container. To remove stale entries, do a
/// binary search on the sorted container and erase all left of the found key.
size_t size_in_bytes = 0;
size_t max_size_in_bytes;
size_t max_count;
WeightFunction weight_function;
IsStaleFunction is_stale_function;
/// TODO support OnWeightLossFunction callback
};
}
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