[erlang-questions] ssh_sftp:read_file

[József Bérces]

Comparing the ssh_sftp:read_file execution time to command line sftp shows a big difference. I experimented with a ~7MB gzipped file, downloading it from a Debian machine to my Win7 laptop. I tested it with Erlang R15B03, R16B02 and R16B03-1.

While the Cygwin sftp transferred it in 4 seconds at 1.7MB/s speed, ssh_sftp:read_file got it in 30-20 seconds, depending on the erlang version. R16B03-1 shows improvement compared to the older releases, so it got the file in ~20s (the older ones needed ~30s).

Writing a small program and using ssh_sftp:read to get the file in 64KB chunks speeds up the file transfer on all releases. The best I got with this is ~11 seconds on R16B03-1 (~20s on the older Erlang releases). But that is still far from the 4 seconds of the Cygwin command line sftp.

Is there a way to further speed up the sftp file transfers in Erlang to reach (or at least to get near to) the command line sftp?

Thanks,
Jozsef
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