plinehan's questions

I like to fully-load our compute hardware to reduce wasted CPU time, and on typical in-house hardware this is fairly easy: load the machine with as many runnable threads as there are cores, and idle time will go to zero.

Here is an example app:

public class Looper
{
    public static void main(String[] args)
    {
        while (true) { new java.util.Random().nextBytes(new byte[4096]); }
    }
}

On our in-house, 8-core hardware, I can run 8 of these and idle time (as reported by mpstat and top) goes to zero. I can even add a 9th, 10th, etc process, and idle time stays very close to zero.

On EC2 (c1.xlarge instances), however, idle time is much higher than I'd expect. At 8 processes, idle time hovers around %1, and with 9, 10, etc processes, it can increase to 2%-3% or higher. With more complicated programs (not the example above), idle time can be even higher than that.

Can anyone explain this? This is with very recent Amazon kernels, and does not include stolen CPU time, which I would expect to see on EC2. Is this a problem with EC2 in particular, or is it general to Xen? Are there known workarounds?

What steps must one take to ensure that an otherwise defaultly-configured InnoDB server is truly ACID compliant? The InnoDB configuration page mentions that the hardware itself must be configured to honor fsync calls, i.e. disable any write-back caches.

This page mentions some other concerns, but may be conflating the binary log and the InnoDB log, and may be a bit out of date regarding default settings for MySQL 5.x.

Upon reading the binary log document page it would seem that the "sync_binlog=1" setting is not required for ACID properties in general, only for ACID properties vis a vis point-in-time recovery and replication.

So, is disabling write-back disk caching sufficient, or are there other settings that must be tweaked?

Is there any way to force SSH to use a particular shell on the remote end, regardless of what the user's default shell is?

I've tried solutions akin to:

ssh host.domain.com /bin/bash -c 'complicated, multi-line command'

but unfortunately the default shell on the remote end is responsible for parsing the "complicated, multi-line command" part, and I'm having difficulty escaping it sufficiently to work both for Bash and C shell users.