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.
{
    static_cast<void>(getEmbeddedDictionariesImpl(true));
}
void Context::setProgressCallback(ProgressCallback callback)
{
    
    progress_callback = callback;
}
ProgressCallback Context::getProgressCallback() const
{
    return progress_callback;
}
void Context::setProcessListElement(ProcessList::Element * elem)
{
    
    process_list_elem = elem;
}
ProcessList::Element * Context::getProcessListElement() const
{
    return process_list_elem;
}
void Context::setUncompressedCache(size_t max_size_in_bytes)
{
    auto lock = getLock();
    if (shared->uncompressed_cache)
        throw Exception("Uncompressed cache has been already created.", ErrorCodes::LOGICAL_ERROR);
    shared->uncompressed_cache = std::make_shared<UncompressedCache>(max_size_in_bytes);
}
UncompressedCachePtr Context::getUncompressedCache() const