Jeethu's Blog

Finally after 2 hours or hard work, I got tagz up and running. Its currently running on my vps (the same machine which was running the staging server).

Here’s the background on the issue.
The main server was running Ubuntu 8.04 (Hardy Heron)
Last night, I ran a standard apt-get update; apt-get upgrade.
It upgraded libc and libc-dev, and that was it. After that, all perl processes would just hang spinning busy on the cpu. I couldn’t do a thing. Tried running a couple of the offending scripts in strace, and they all hang on a clone() syscall. Tried restarting the AMI, but it still persisted. The worst problem was I couldn’t even get a db dump because pg_dump wouldn’t work. And the last snapshot I had was about 17 hours old.

So, here’s what I did. I terminated the postmaster instance, took a backup of the db directory, scp’d it to my vps and tried using it there. Then I found that I had to recompile postgresql with –enable-integer-datetimes for it to accept the database. Did that and few other tweaks (I’d switched DNS to point to the VPS early on) and here we have it, up and running.

I’ve got to move back to EC2 soon (The VPS wouldn’t be able to handle the loads for long). But this time, I’m going back to Debian Stable, I’ve had enough of Ubuntu, I have no idea how something as innocuous as a libc upgrade can barf things up so badly.

Due to a libc upgrade gone awry, tagz.in has been down for the past 30 minutes. I’m working on bringing it up asap.

UPDATE: Its up again, on a different machine.

This one’s pretty basic (from the docs) , but I end up using it all the times. Being able to “AND” and “OR” django querysets can really simplify a lot of code. Here’s an instance (a simplification of the setup I have in tagz). Lets start by defining 2 models.

from django.db import models

class Tag( models.Model ) :
    text = models.CharField(max_length=255)

class Post( models.Model ) :
    link  = models.URLField(max_length=2048)
    title = models.CharField(max_length=255)
    tags  = models.ManyToManyField(Tag)

Now, lets say I want to get all Posts tagged as django or python.

qs = Post.objects.filter(tags__text='python') | Post.objects.filter(tags__text='django')

Now as intuitive as it might seem, using AND doesn’t seem to work.

qs = Post.objects.filter(tags__text='python') & Post.objects.filter(tags__text='django')
# qs.count() returns 0

So, we end up chaining filters like this:

qs = Post.objects.filter(tags__text='python').filter(tags__text='django')

Which boils down to simple for loop.

def filter_tags( tags ) :
    '''
    tags: a list of strings
    '''
    p = Post.objects.all()
    for t in tags :
        p = p.filter(tags__text=t)
    return p