Forcibly-unbuffered redirect-to-pipe yields terrible perf

[alexandre.ferrieux]

Hi,

When writing into a pipe redirection:

        gawk '{print | "cat > /tmp/foo"}'

... gawk *always* handles the pipe as unbuffered. This can be witnessed with an 
external "tail -f /tmp/foo".

This makes gawk completely unusable for any heavy-duty multipipe output, as CPU 
time is dominated by single-line write() syscalls.

By contrast, heavy-duty multifile output *is* supported:

        gawk '{print  > "/tmp/foo"}'

... is fully buffered. What is the logic behind this difference ?
Note: it can be traced to this commit:

3697ec5c  Arnold D. Robbins  Thu Jul 15 23:12:49 2010 +0300  Moved to gawk 2.11.

.. with the following comment:

> Improved handling of output bufferring:  now all print[f]s redirected to a tty
> or pipe are flushed immediately and non-redirected output to a tty is flushed
> before the next input record is read.

Before this commit, the programmer had the choice; they could call fflush() or 
not, so that both "interactive" and "efficient" use cases were supported.
Afterwards, the choice has disappeared: any write to a pipe is deemed 
"interactive", incurring a syscall, and terrible performance.

Can someone explain why this is an improvement ?

PS: I do realize this has been the case for 13 years. But maybe it wasn't 
spotted before, precisely because Awk was too slow for such heavy-duty tasks, 
back in the days. Now things are different: Awk is a serious candidate for 
scientific computing, and such details are just starting to be a problem.

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