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Poor HTTP POST upload performance

From: Bryan Christ <>
Date: Mon, 13 Apr 2015 21:01:11 -0500

I've been trying to figure out why http POST uploads are so slow with
libcurl. Upload speeds continually perform at about 1/10th of the expected
performance (or less). Many users have reported this behavior on our
forum. I suspect it has a lot to do with CURL_MAX_WRITE_SIZE being set to
16k. Uploads to these same servers through other means (JavaScript for
example) reach their expected throughput. The code in question can be seen
here: (at
approx line 314)

Assuming the issue is the 16K buffer limit, are there any other options?
Asking users to recompile a custom libcurl with a larger buffer size is not
very palatable.


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Received on 2015-04-14