Don't invoke r.log() if not r.debug

[colega]

Profiling shows that up to 40% of our allocations happen in r.markRead(): just to allocate a slice to pass the "remain" arg, which will be discarded because we don't run with r.debug=true.

  Total:    64259028   64259028 (flat, cum) 41.57%
    350            .          .           	if r.count == 0 { 
    351            .          .           		panic("markRead: negative count") 
    352            .          .           	} 
    353            .          .           	r.count-- 
    354            .          .           	r.unwindStack() 
    355     64259028   64259028           	r.log("Mark read remain=%d", r.remain) 
    356            .          .           } 
    357            .          .            
    358            .          .           func (r *messageSetReader) unwindStack() { 
    359            .          .           	for r.count == 0 { 
    360            .          .           		if r.remain == 0 { 

This makes the code slightly verbose, having to check the debug mode before invoking r.log(), but it's a huge difference in high-throughput applications.

[replay]

🚀

[replay]

are you planning to PR upstream as well?

[colega]

Yes, already sent in segmentio#1110