Hi, Daniel,

Thank you very much for your explanation. Can the buffer size in libcurl be
changed by any settings externally? If not, Can I try to modify this buffer
size in libcurl source code and recompile it to get a new version of
libcurl?
On the top of libcurl, there is one more level- libssh2. Does it also have
any buffer size issue?

50% of speed loss will be acceptable if sftp is compared to ftp. We really
need to improve sftp download speed to make it w

Thanks,
Michael

-----Original Message-----
From: Daniel Stenberg
Sent: Thursday, April 24, 2014 2:13 AM
To: the curl tool
Subject: Re: very slow sftp download speed

On Wed, 23 Apr 2014, Michael Zhang wrote:

> I did a test today with Curl 7.36.0 and a sftp server and found one issue.
> Although Curl is able to download small files from the server via sftp,
> its downloading speed for larger files such as 6.6GB is really slow. I did
> a comparison between sftp and ftp.

Yes, this is a known problem/flaw with curl and libcurl doing SFTP. I've
repeated it many times but I guess I've not made a very good job of
explaining
in detail why and what needs to be done so I'll try to do that and blog
something about it later on.

The primary reason is that SFTP is a funny protocol. To work around that
dilemma, a (much) larger buffer is necessary to use, but libcurl only uses a
fixed-size fairly small one that is the same for all protocols.

This is a solvable problem but I've not yet seen anyone really interested in
fixing it.

-- 
  / daniel.haxx.se
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