nice ssh2 in php

Question

I have a php script that transfers a bunch of files between servers with the pecl ssh2 extension (ssh2_sftp_* for the most part). These files add up to about a gig or so each time. The bandwidth is throttled, so that's not a problem. The problem is the ssh2 process eats up a ton of CPU and actually slows down the server during the upload. Is there any way to start the ssh process at a certain nice level? If php's ssh2 functions create a new process (I'm not sure that they do), is it possible to find and renice this process once it's been started from within the php script? Since the ssh2 functions are not threaded, there probably isn't.

Basically, I'd like PHP's ssh2 functions not to use so much CPU. It seems like proc_nice will do this, but it looks like I may have to use ionice instead. How can I do that?

Answer 1

A short look at the sources of PEAR::ssh2 shows, that the SSH2 functions are executed in-thread and in-process, so there is no real straight-forward way. Here are a two possibilities:

• If you are on a multi-process apache use proc_nice to reduce priority, then apache_child_terminate to kill the process.
• Use proc_open or friends to open a shellscript of the type

#!/bin/bash
read SRCFILE
read DSTFILE
nice scp "$SRCFILE" "$DSTFILE"

We use the latter for quite a lot of CPU-hogging tasks