Comments on: Zonelimits State: The Silent Killer

By: Jason Thomas

Jason Thomas — Thu, 05 Mar 2009 22:05:12 +0000

As noticed with one of our servers, reducing the send/receive window to such a low value will decrease the maximum transfer throughput of the server. This might be okay if you are serving small files, however when large files are in question it becomes an issue.

throughput <= Receive Window / Round Trip Time of Path

If your Round Trip Time of Path is equal to 90 ms, usually the case on a transatlantic link, the throughput value is calculated below:

throughput <= 8192 Bytes / .09 second
throughput <= 91 KBytes/second

The receive window value could remain low if you are not uploading large amount of content, however send window should be higher so that clients with higher latency get better speeds.

By: Chris

Chris — Tue, 13 Jan 2009 07:28:00 +0000

Thats true, moreso for LAN connections, I’ve found that an improved route on the WAN interface by far surpasses any work you can do with tcp buffers. Also this is optimizing for loads of connections, not just for a few connections having speed. It depends whether or not you want to secrifice a bit in speed for a big increase in network connections.

By: Mxx

Mxx — Tue, 13 Jan 2009 02:43:23 +0000

but doesn’t decreasing recvspace and sendspace can limit maximum potential throughput on high bandwidth/high latency connections
(ala calibeach..)

By: Chris

Chris — Tue, 30 Dec 2008 17:52:25 +0000

Thanks, I searched for a long time online to find the answer to this so thought it needed to be shared.

By: izo

izo — Tue, 30 Dec 2008 17:46:35 +0000

Otherwise, great job. You Rock !!!

By: izo

izo — Tue, 30 Dec 2008 17:44:59 +0000

The last command is missing an ‘s’, should be –
sysctl net.inet.tcp.recvspace=8192