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#include <Storages/Cache/SchemaCache.h>
#include <Common/ProfileEvents.h>
#include <ctime>
namespace ProfileEvents
{
extern const Event SchemaInferenceCacheHits;
extern const Event SchemaInferenceCacheSchemaHits;
extern const Event SchemaInferenceCacheNumRowsHits;
extern const Event SchemaInferenceCacheMisses;
extern const Event SchemaInferenceCacheSchemaMisses;
extern const Event SchemaInferenceCacheNumRowsMisses;
extern const Event SchemaInferenceCacheEvictions;
extern const Event SchemaInferenceCacheInvalidations;
}
namespace DB
{
SchemaCache::SchemaCache(size_t max_elements_) : max_elements(max_elements_)
{
}
void SchemaCache::addColumns(const Key & key, const ColumnsDescription & columns)
{
std::lock_guard lock(mutex);
addUnlocked(key, columns, std::nullopt);
}
void SchemaCache::addManyColumns(const Keys & keys, const ColumnsDescription & columns)
{
std::lock_guard lock(mutex);
for (const auto & key : keys)
addUnlocked(key, columns, std::nullopt);
}
void SchemaCache::addNumRows(const DB::SchemaCache::Key & key, size_t num_rows)
{
std::lock_guard lock(mutex);
addUnlocked(key, std::nullopt, num_rows);
}
void SchemaCache::addUnlocked(const Key & key, const std::optional<ColumnsDescription> & columns, std::optional<size_t> num_rows)
{
/// Update columns/num_rows with new values if this key is already in cache.
if (auto it = data.find(key); it != data.end())
{
if (columns)
it->second.schema_info.columns = columns;
if (num_rows)
it->second.schema_info.num_rows = num_rows;
return;
}
time_t now = std::time(nullptr);
auto it = queue.insert(queue.end(), key);
data[key] = {SchemaInfo{columns, num_rows, now}, it};
checkOverflow();
}
void SchemaCache::checkOverflow()
{
if (queue.size() <= max_elements)
return;
auto key = queue.front();
data.erase(key);
queue.pop_front();
ProfileEvents::increment(ProfileEvents::SchemaInferenceCacheEvictions);
}
std::optional<ColumnsDescription> SchemaCache::tryGetColumns(const DB::SchemaCache::Key & key, DB::SchemaCache::LastModificationTimeGetter get_last_mod_time)
{
auto schema_info = tryGetImpl(key, get_last_mod_time);
if (!schema_info)
return std::nullopt;
if (schema_info->columns)
ProfileEvents::increment(ProfileEvents::SchemaInferenceCacheSchemaHits);
else
ProfileEvents::increment(ProfileEvents::SchemaInferenceCacheSchemaMisses);
return schema_info->columns;
}
std::optional<size_t> SchemaCache::tryGetNumRows(const DB::SchemaCache::Key & key, DB::SchemaCache::LastModificationTimeGetter get_last_mod_time)
{
auto schema_info = tryGetImpl(key, get_last_mod_time);
if (!schema_info)
return std::nullopt;
if (schema_info->num_rows)
ProfileEvents::increment(ProfileEvents::SchemaInferenceCacheNumRowsHits);
else
ProfileEvents::increment(ProfileEvents::SchemaInferenceCacheNumRowsMisses);
return schema_info->num_rows;
}
std::optional<SchemaCache::SchemaInfo> SchemaCache::tryGetImpl(const Key & key, LastModificationTimeGetter get_last_mod_time)
{
std::lock_guard lock(mutex);
auto it = data.find(key);
if (it == data.end())
{
ProfileEvents::increment(ProfileEvents::SchemaInferenceCacheMisses);
return std::nullopt;
}
ProfileEvents::increment(ProfileEvents::SchemaInferenceCacheHits);
auto & schema_info = it->second.schema_info;
auto & queue_iterator = it->second.iterator;
if (get_last_mod_time)
{
/// It's important to call get_last_mod_time only if we have key in cache,
/// because this function can do some heavy operations.
auto last_mod_time = get_last_mod_time();
/// If get_last_mod_time function was provided but it returned nullopt, it means that
/// it failed to get last modification time, so we cannot safely use value from cache.
if (!last_mod_time)
return std::nullopt;
if (*last_mod_time >= schema_info.registration_time)
{
/// Object was modified after it was added in cache.
/// So, stored value is no more valid and we should remove it.
ProfileEvents::increment(ProfileEvents::SchemaInferenceCacheInvalidations);
queue.erase(queue_iterator);
data.erase(key);
return std::nullopt;
}
}
/// Move key to the end of queue.
queue.splice(queue.end(), queue, queue_iterator);
return schema_info;
}
void SchemaCache::clear()
{
std::lock_guard lock(mutex);
data.clear();
queue.clear();
}
std::unordered_map<SchemaCache::Key, SchemaCache::SchemaInfo, SchemaCache::KeyHash> SchemaCache::getAll()
{
std::lock_guard lock(mutex);
std::unordered_map<Key, SchemaCache::SchemaInfo, SchemaCache::KeyHash> result;
for (const auto & [key, value] : data)
result[key] = value.schema_info;
return result;
}
}
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