select formatReadableSize(sum(bytes_allocated)) from system.dictionaries;

SELECT
    database,
    name,
    formatReadableSize(total_bytes)
FROM system.tables
WHERE engine = 'Memory'

select formatReadableSize(sum(memory_usage)) from system.merges;

select formatReadableSize(sum(memory_usage)) from system.processes;

SELECT
    initial_query_id,
    formatReadableSize(memory_usage),
    formatReadableSize(peak_memory_usage),
    query
FROM system.processes
ORDER BY peak_memory_usage DESC
LIMIT 10

SELECT
    initial_query_id,
    formatReadableSize(memory_usage),
    query
FROM system.query_log
WHERE (event_date >= today()) AND (event_time >= (now() - 7200))
ORDER BY memory_usage DESC
LIMIT 10

SELECT toDate(0)
┌──toDate(0)─┐
│ 1970-01-01 │
└────────────┘