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);
    if (shared->merge_tree_disk_selector)
        shared->merge_tree_disk_selector = shared->merge_tree_disk_selector->updateFromConfig(config, "storage_configuration.disks", *this);
    if (shared->merge_tree_storage_policy_selector)
    {
        try
        {
            shared->merge_tree_storage_policy_selector = shared->merge_tree_storage_policy_selector->updateFromConfig(config, "storage_configuration.policies", shared->merge_tree_disk_selector);
        }
        catch (Exception & e)
        {
            LOG_ERROR(shared->log, "An error has occurred while reloading storage policies, storage policies were not applied: {}", e.message());
        }
    }
#if !defined(ARCADIA_BUILD)
    if (shared->storage_s3_settings)
    {
        shared->storage_s3_settings->loadFromConfig("s3", config);
    }
#endif
}
const MergeTreeSettings & Context::getMergeTreeSettings() const