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Re: How to do optimal FTP upload for multiple files?

From: Taras Kushnir via curl-library <>
Date: Thu, 18 Jul 2019 15:06:51 +0000

Thanks for your time Daniel!

I will remove UPLOAD_BUFFERSIZE tuning for use with 7.65.1. Yeah, I saw this topic when I was looking for the solution, but the latest summary it has is that “there’s no good solution” which kind of depressed me a little bit.

Can I investigate slowness using 7.65 (since it has same changes) or do I need to use 7.61 specifically?

> On Jul 18, 2019, at 00:04, Daniel Jeliński via curl-library <> wrote:
> Taras,
> Thanks for pointing that out. The function looks good.
> Buffer autotuning was only introduced in curl 7.61, so the app using
> 7.57 will use the default (slow) buffer sizes. You shouldn't need to
> set UPLOAD_BUFFERSIZE to get good upload speeds on 7.65.1.
> As for the connection timeout, it appears to be a well known problem
> with FTP on slow connections with oversized buffers. I just found a 10
> year old message describing what looks like the same problem:
> I checked your upload_failure log, specifically the connection logged
> under T#12216. This connection appears to have ~100ms RTT, throughput
> ~5KB per RTT (50KB/s), for which the default 16KB buffer looks like
> overkill. In that environment sending the last ~700KB buffer would
> take about 15 seconds; curl timed out after 10. So yes, this problem
> was indeed caused by oversized UPLOAD_BUFFERSIZE.
> Back to slowness topic, can you reproduce the slow uploads using curl
> binary version 7.61 or newer?
> Regards,
> Daniel
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Received on 2019-07-18