Normally, you debug, and when that’s done, you profile to speed things up.

That said, today I was confronted by a problem where profiling actually helpped the debugging.

A page, that should be working 100% from memcache was hitting mysql, 2 million times a day.

This page was on a serveur that couldn’t be debugged remotly. Two options were available, I could either put “print”s everywhere, and hoped to get lucky, or I could run the pager through xdebug’s profiler.

Loading the resulting profile into KCacheGrind, I had a detailled run down of every code path taken available to me. All that was rest was to lookup all mysql calls and work back up from caller to caller to identify the bug.

If you have a high bandwidth site, and are seeing high load, lots of time waiting for io and nginx processes in the D state a lot, here’s something you could try:

First of all, install iotop and make sure nginx is the culprit (lots of IO for nginx, not much for the rest)

Then, go and have a look at your NGinx configuration, (nginx.conf), especially the worker_processes

You can try pushing the value up to (and maybe even over) the number of cores you have in your system. This spreads the load more evenly, and allows you to dramatically increase disk throughput (doubling isn’t uncommon).

This worked for me (going from 3Mb/s to 7Mb/s peak). That said, YMMV.

Feel free to leave a comment to say if/how this was (un)helpful

My deepest apologies .

To understand what happened, here’s a quick lowdown on how my setup works:

I’m self hosting this blog as well as my mail on a converted EasyGate that I got as a beta tester. The machine is connected onto my internet router (a Trio 3D antique) and then onto the internet. My ISP provides a temporary IP address, and as such, I need to use a dynamic DNS record to be able to keep things updated.

Now, the Trio 3D (as with most of it’s features) has a half assed (excuse my French)  DynDNS system built in. I say half assed because it doesn’t accept any provider except the historic DynDNS and because it quite often forgets to update. Last week it completely stopped updating, and as an added bonus, I couldn’t get back into DynDNS to do things manually.

As a work around, I set up OVH (who are my registrar) to route my DNSes manually until I got a permanent fix. That worked until the IP changed Tuesday or Wednesday.

Now things are sorted out. I’m using OVH’s own DynDNS servers (much simpler) and am using a home built client to avoid all the dependancies other clients bought in.

The client is written in bash and depends on bash, sed and wget to work. It’s best used in a cron job, but can also be run on interface specific events if need be.

It uses a web based IP fetcher to work out your IP adresse, and if it’s changed since you last run the script, it updates your DynDNS records for you.

Without further ado, here’s the code:

#/bin/bash

USERNAME='myusername'
PASSWORD='mypassword'
HOSTS=('first_url.test.com' 'second_url.test.com')
SERVER="www.ovh.com"

#
#
#

CURRENT_IP=`wget -O - 'http://checkip.dyndns.org/' 2>/dev/null | sed -e 's/.*Address: \([^<]*\).*/\1/'` if [ -f /tmp/my_ip ]; then 	OLD_IP=`cat /tmp/my_ip`; fi # # Don't update unless ip has changed # if [ "x"$CURRENT_IP == "x"$OLD_IP ]; then 	exit; fi; echo "IP changed from " $OLD_IP " to " $CURRENT_IP echo "Saving new IP" echo $CURRENT_IP > /tmp/my_ip

for HOST in ${HOSTS[@]};
do
	echo "Updating " $HOST " to " $CURRENT_IP
	wget -O - "http://${USERNAME}:${PASSWORD}@${SERVER}/nic/update?system=dyndns&hostname=${HOST}&myip=${CURRENT_IP}&wildcard=NOCHG&mx=NOCHG&backmx=NOCHG" 2>/dev/null
	echo ""
done

Et voila, I hope this helps someone out there

(No deb instructions this time since I’ve passed on to arch, which has a perfectly functional package).

A couple of thing seem to have changed though, namely:

• Bitrates are now in bytes/seconde rather than kbytes/seconde (unless otherwise stated)
• AAC is no longer an encoder module (use libfaac)
• mp4/amr containers don’t seem to work to well with libfaac, use 3gp instead to be safe.

Which gives:

 ffmpeg -i input.avi -vcodec h263 -b 409600 -s 352x288 -acodec libfaac -ab 65536 -ar 48000 -ac 2 -f 3gp output.3gp

Happy encoding

Go to your browser, type in www.google.com, you get the google home page. Everythings normal there.

Now, change your url, ad a dot (so that it reads www.google.com.) . The page still loads.

This is risky, since it can lead to a duplicate content malus on google, but is perfectly normal DNS behaviour.

The actual FQDN is www.google.com. . It’s just that, to make our lives easier, the last dot is optional.

Unfortunatly, there’s no way to get rid of them (even 301s seem flaky).

That’s all, just so that the next time you see bizzars urls, you have a reason for them all ready for your boss

For once, the new machine is less powerful than the old.

This blog is now running on an opengate with 512Mb ram and 512Mb of disk (!)

The small install size (systme + data <400Mb) is obtained by using a basic Debian install, and by taking a rm to most of the documentation and things like that.

I might even try to get it down to under 300Mb soon.

Unfortunatly my servers sleep turned out to be the big sleep, and this morning it refused to start.

A few hours and a HD transplant later, evrything is back on line, now running on a Semperon 2600 and 1Go of ram

This is painfully obvious with AAC and the formats that use it (think mp4).

Luckally, playback can be assured by using a nice arrangement of plugins that are downloaded just in time to play the offending file on your computer (thanks ubuntu).

This help doesn’t extend to re-encoding though, so for those of you lucky enough to have an mp4 capable phone (like the sony erricsons), you can find that putting the latest Bleach on your phone to be an exercise in frustration.

The reasons for this are numerous and complexe but come down to the simple fact that if cannonicle put aac encoders in Ubuntu they’d be sued to kingdom come in the states (thank god I don’t live there ).

Help is at hand though, since even if the versions of the enncoding tools included with Ubuntu don’t come equiped, you can re-compile them so that they work as intended.

First up: ffmpeg

FFmpeg is one of the many swiss army knives used for video encoding available with Linux. It’s probably the easiest to use, and like it’s cousins, the ubuntu version comes cripled.

What to do?

First of all, make sure we have what’s needed to re-build it

sudo apt-get build-dep ffmpeg

Then add a few libraries (that add the magic support)

sudo apt-get install libfaac-dev libfaac0 libfaad-dev libfaad2-0 libfaad0

Finally, get the source code to ffmpeg

mkdir ffmpeg
cd ffmpeg
apt-get source ffmpeg

Now the fun starts, you should have 3 files and a directory before you.

Cd into the directory.

Now let’s move this thing arround a bit:

Open: debian/rules

This file tells dpkg how to build ffmpeg, we want to add a config flag so go to the lines that start with “confflags” and add on to one of them:

–enable-libfaad –enable-libfaac

Save, and quit, now all you have to do is re-build the package

dpkg-buildpackage

go have a coffee while it builds, and then install the result:

cd ..
dpkg -i ffmpeg*

To use, something like this is needed:

ffmpeg -i Source.avi -vcodec h263 -b 400 -s 352×288 -acodec aac -ab 64 -ar 48000 -ac 2 -f mp4 Dest.mp4

Update:

For eugenia (and anyone else who also wants AMR support), here are the debs with it (supported in the ‘if it breaks you get to keep both pieces’ way since I haven’t got the means to test them atm:

Update :

I’ve removed the download links for now since the files aren’t available on my server any longer. If anyone needs them, let me know

The only problem came from the kernel, which now calls  ide drives ‘sd…’ instead of ‘hd…’ so hda1 becomes sda1.

Update grub or face the consequances.You have been warned!

That’s what happened to me with Zabbix yesterday. I was going through some items and cleaning up, when suddenly, 4 hosts went off-line. Except that they hadn’t.

I couldn’t understand why Zabbix refused to see them (the agents were responding fine).

I finally found out that it was because of the way that Zabbix calculates the ‘status’ item, which has a value of 0 if alls well, and 2 if the host is off-line.

Zabbix looks at the first item to be taken of the host, if that item returns an empty string, Zabbix decides that the host is dead and raises the alarm, even if the host has 150 other items all working perfectly. This bizzar to say the least, but workable. If this happens, a quick fix is to deactivate the offending Item, so that the first Item checked returns a value, then the host comes back

Any how, I thought I’d just document this in case anyone else starts loosing hair over the issue