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->clusters_mutex);
    shared->clusters_config = config;
    if (!shared->clusters)
        shared->clusters = std::make_unique<Clusters>(*shared->clusters_config, settings, config_name);
    else
        shared->clusters->updateClusters(*shared->clusters_config, settings, config_name);
}
void Context::setCluster(const String & cluster_name, const std::shared_ptr<Cluster> & cluster)
{
    std::lock_guard lock(shared->clusters_mutex);
    if (!shared->clusters)
        throw Exception("Clusters are not set", ErrorCodes::LOGICAL_ERROR);
    shared->clusters->setCluster(cluster_name, cluster);
}
void Context::initializeSystemLogs()
{
    auto lock = getLock();
    shared->system_logs.emplace(*global_context, getConfigRef());
}
void Context::initializeTraceCollector()
{
    shared->initializeTraceCollector(getTraceLog());
}
bool Context::hasTraceCollector() const
{
    return shared->hasTraceCollector();
}
std::shared_ptr<QueryLog> Context::getQueryLog()