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();
    return settings;
}
void Context::setSettings(const Settings & settings_)
{
    auto lock = getLock();
    auto old_readonly = settings.readonly;
    auto old_allow_ddl = settings.allow_ddl;
    auto old_allow_introspection_functions = settings.allow_introspection_functions;
    settings = settings_;
    if ((settings.readonly != old_readonly) || (settings.allow_ddl != old_allow_ddl) || (settings.allow_introspection_functions != old_allow_introspection_functions))
        calculateAccessRights();
}
void Context::setSetting(const StringRef & name, const String & value)
{
    auto lock = getLock();
    if (name == "profile")
    {
        setProfile(value);
        return;
    }
    settings.set(std::string_view{name}, value);
    if (name == "readonly" || name == "allow_ddl" || name == "allow_introspection_functions")
        calculateAccessRights();
}
void Context::setSetting(const StringRef & name, const Field & value)