When I queried `system.metrics` table, I found some negative values which hint to some potential internal overflows.

```
SELECT *
FROM system.metrics
FORMAT Vertical

...

Row 31:
───────
metric:      MemoryTrackingInBackgroundProcessingPool
value:       -580863171
description: Total amount of memory (bytes) allocated in background processing pool (that is dedicated for backround merges, mutations and fetches). Note that this value may include a drift when the memory was allocated in a context of background processing pool and freed in other context or vice-versa. This happens naturally due to caches for tables indexes and doesn't indicate memory leaks.

Row 32:
───────
metric:      MemoryTrackingInBackgroundMoveProcessingPool
value:       0
description: Total amount of memory (bytes) allocated in background processing pool (that is dedicated for backround moves). Note that this value may include a drift when the memory was allocated in a context of background processing pool and freed in other context or vice-versa. This happens naturally due to caches for tables indexes and doesn't indicate memory leaks.

Row 33:
───────
metric:      MemoryTrackingInBackgroundSchedulePool
value:       -4461308831
description: Total amount of memory (bytes) allocated in background schedule pool (that is dedicated for bookkeeping tasks of Replicated tables).

...

56 rows in set. Elapsed: 0.003 sec.
```

Server version: 20.8.2.3.
{
    std::lock_guard lock(shared->storage_policies_mutex);
    return getDiskSelector(lock)->getDisksMap();
}
StoragePoliciesMap Context::getPoliciesMap() const
{
    std::lock_guard lock(shared->storage_policies_mutex);
    return getStoragePolicySelector(lock)->getPoliciesMap();
}
DiskSelectorPtr Context::getDiskSelector(std::lock_guard<std::mutex> & ) const
{
    if (!shared->merge_tree_disk_selector)
    {
        constexpr auto config_name = "storage_configuration.disks";
        const auto & config = getConfigRef();
        shared->merge_tree_disk_selector = std::make_shared<DiskSelector>(config, config_name, *this);
    }
    return shared->merge_tree_disk_selector;
}
StoragePolicySelectorPtr Context::getStoragePolicySelector(std::lock_guard<std::mutex> & lock) const
{
    if (!shared->merge_tree_storage_policy_selector)
    {
        constexpr auto config_name = "storage_configuration.policies";
        const auto & config = getConfigRef();
        shared->merge_tree_storage_policy_selector = std::make_shared<StoragePolicySelector>(config, config_name, getDiskSelector(lock));
    }
    return shared->merge_tree_storage_policy_selector;
}
void Context::updateStorageConfiguration(const Poco::Util::AbstractConfiguration & config)