Too high rate of progress information from pg_basebackup

Hi,
it looks that pg_basebackup, when using --progress information, outputs
so much information that it puts cpu pressure on terminal application
I'm using - whether it's simple xterm/rxvt, "screen" or "tmux" terminal
multiplexers.

My specific usecase is setting multiple slave servers for multiple
clusters in AWS, so the data transmission between servers is pretty
fast, but the jump host, that I run all the pg_basebackup (via ssh)
from, is not really beefy, and with 4 concurrent pg_basebackups, I've
seen tmux use up to 80% of CPU of the jump host.

I filled bug report for tmux too, but since the problem can be repeated
in xterm, rxvt, and screen, I think that perhaps it should be handled in
some way in pg_basebackup too?

For completeness sake:
we're using pg_basebackup from 9.3.11 on ubuntu trusty.

In my quick sanity-check test, it looks that progress information in our
case is outputted with the speed of ~ 320KB/s. Which seems excessive.

Best regards,

depesz

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