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.
{
    auto lock = getLock();
    if (!shared->compression_codec_selector)
    {
        constexpr auto config_name = "compression";
        const auto & config = getConfigRef();
        if (config.has(config_name))
            shared->compression_codec_selector = std::make_unique<CompressionCodecSelector>(config, "compression");
        else
            shared->compression_codec_selector = std::make_unique<CompressionCodecSelector>();
    }
    return shared->compression_codec_selector->choose(part_size, part_size_ratio);
}
DiskPtr Context::getDisk(const String & name) const
{
    std::lock_guard lock(shared->storage_policies_mutex);
    auto disk_selector = getDiskSelector(lock);
    return disk_selector->get(name);
}
StoragePolicyPtr Context::getStoragePolicy(const String & name) const
{
    std::lock_guard lock(shared->storage_policies_mutex);
    auto policy_selector = getStoragePolicySelector(lock);
    return policy_selector->get(name);
}
DisksMap Context::getDisksMap() const