[Hackage] #447: do parallel builds

Curt Sampson cjs at starling-software.com
Sat Jan 17 22:54:51 EST 2009

On 2009-01-17 17:16 +0000 (Sat), Duncan Coutts wrote:

> On Wed, 2009-01-14 at 00:09 +0900, Curt Sampson wrote:
> > ..parallel downloads are a very happy thing; in some circumstances I can
> > run a dozen downloads in parallel, without any individual one being
> > slower than it would be running alone.
> Presumably to different servers though right?

No; to a single server. There still appear to be a lot of TCP
implementations out there not supporting the extensions necessary to
increase window size beyond 64K, meaning that at any time only 64K of
unacknowledged data can be outstanding on the connection. For me, a
250 ms. round-trip-time (RTT) is not unusual, meaning that the minimum
amount of time between the server sending a segment and getting my
client's acknowledgement of receipt is 250 ms. That means that, no
matter how much bandwidth is available, I'll never see more than 256
KB/sec, or so, which is a small fraction (1/40th) of the available
bandwidth between me and a server in the US with at least a 100 Mbps

> I was also under the impression that most web servers kind of frowned on
> more than one or two connections from the same client and some would
> take active measures to prevent it.

Not that I'm aware of. Most have this capability, and some people chose
to use it when they it solves a problem for them, but I haven't found it
to be that terribly common.

And of course there's also the case where the files one downloads are
on different servers, either because the one "server" from which you're
downloading is actually a cluster (a common case with larger sites) or
because the things your downloading are actually hosted by different

Curt Sampson       <cjs at starling-software.com>        +81 90 7737 2974
           Functional programming in all senses of the word:

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