PQ can exceed queue.max_bytes

[kaisecheng]

Currently, the queue size is the sum of the event size per tail page and head page. Some pages may have 100kb event, some may have 30mb. However, pages are immutable and consume a fixed size, default 64mb, on disk. So, the size calculation should take the capacity not the event size. Hence, the current PQ can consume more than the queue.max_bytes

[kaisecheng]

Check comment for the queue max size assumption