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Re: Getting files from SFTP is slower at newer versions

From: Moti Avrahami <>
Date: Sun, 15 May 2016 15:27:22 +0300

I measure a downgrade of more 35% download time.
I tried also to enlarge the CURL_MAX_WRITE_SIZE to 256K - 4MB but it
doesn't improve the times.
I am trying now to upgrade libssh2 to 1.7.0. Although I encounter some
compilation errors (is there a specific Visual Studio version that is
recommended for it?) I feel it will take me less time than trying to find
the problem during debugging.


On Sun, May 15, 2016 at 12:45 PM, Daniel Stenberg <> wrote:

> On Sun, 15 May 2016, Moti Avrahami wrote:
> I recently upgraded my libcurl version from 7.19.4 to 7.47.1 and I noticed
>> that there is a performance downgrade when downloading files from SFTP
>> servers than the older libcurl version.
>> I checked both versions against the same SFTP servers.
>> I use libssh2 version 1.4.1.
>> Does anyone know what is reason and how can I fix it?
> I don't know the reason. But you're doing a *massive* upgrade bump so
> almost everything has been changed internally. Clearly at some point the
> SFTP performance got worse. How big is the speed difference you measure?
> What's the latency to the server in your test case?
> You're also using an outdated libssh2 version. It has improved through
> time and modern versions should be faster and more reliable.
> The way to track this down is through good old fashioned debugging. You
> can possibly bisect yourself to the actual offending commit (assuming it
> was a single specific one) and based on knowing which change it was we can
> perhaps find the culprit/explanation faster.
> I've written about (poor) SFTP performance in libcurl several times in the
> past and we have ideas on how it could be increased significantly, but
> unfortunately nobody has yet actually converted any of those thoughts into
> reality. One such mention is here:
> --
> /
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Received on 2016-05-15