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.
{
    return getClusters().getCluster(cluster_name);
}
void Context::reloadClusterConfig()
{
    while (true)
    {
        ConfigurationPtr cluster_config;
        {
            std::lock_guard lock(shared->clusters_mutex);
            cluster_config = shared->clusters_config;
        }
        const auto & config = cluster_config ? *cluster_config : getConfigRef();
        auto new_clusters = std::make_unique<Clusters>(config, settings);
        {
            std::lock_guard lock(shared->clusters_mutex);
            if (shared->clusters_config.get() == cluster_config.get())
            {
                shared->clusters = std::move(new_clusters);
                return;
            }
            
        }
    }
}
Clusters & Context::getClusters() const