Netuality

A newcomer in the world of “code snippets” sites in programmingishard.com. Although the site is a few months old, only recently it started to gain some steam. Unlike its competition Krugle and Koders, this is not a code search engine but a snippet repository entirely tag-based, user-built. The author has a blog at tentimesbetter.com.

As for watering your mouth, this is a Python code fragment that I found on the site, for the classic inline conditional which does not exist “such as” in Python:

n = ['no', 'yes'][thing == 1]

Obviously it has the big disadvantage of having to compute both values no matter what the condition thing is, but is very short and elegant. Simple but nice code sugar.

Memcached is a clusterable cache server from Danga. Or, as they call, it a distributed memory object caching system. Well, whatever. Just note that memcached clients exist for lots of languages (Java, PHP, Python, Ruby, Perl) – mainstream languages in the web world. A lighter version of server was rewritten in Java by Mr. Jehiah Czebotar. Major websites such as Facebook, Slashdot, Livejournal and Dealnews use memcached in order to scale for the huge load they’re serving. Recently, we needed to monitor the memcache servers on a high-performance web cluster serving the Planigo websites. By googling and reading the related newsgroups, I was able to find two solutions:

• from faemalia.net, a script which is integrated with the MySQL server templates for Cacti. Uses the Perl client.
• from dealnews.com, a dedicated memcached template for Cacti and some scripts based on the Python client. The installation is thoroughly described here.

These two solutions have the same approach – provide a specialized Cacti template. The charts drawn by these templates are based on data extracted by the execution of memcached client scripts. Maybe very elegant, but could become a pain in the dorsal area. Futzing with Cacti templates was never my favorite pasttime. Just try to import a template exported from a different version of Cacti and you’ll know what I mean. In my opinion, there is a simple way, which consists in installing a memcached client on all the memcached servers, then extracting the statistical values using a script. We’ll use the technique described in one of my previous posts, to expose script results as SNMP OID values. Then, track these values in Cacti via the generic existing mechanism. My approach has the disadvantage of installing a memcached client on all the servers. However, it is very simple to build your own charts and data source templates, as for any generic SNMP data. All you need now a simple script which will print the memcached statistics, one per line. I will provide one-liners for Python, which will obviously work only on machines having Python and the “tummy” client installed. This is the recipe (default location of Python executable on Debian is /usr/bin/python but YMMV):

1. first use this one liner as snmpd exec :

/usr/bin/python -c “import memcache; print (‘%s’%[memcache.Client(['127.0.0.1:11211'], debug=0).get_stats()[0][1],]).replace(“‘”,”).replace(‘,’,'n’).replace(‘[','')
.replace(']‘,”).replace(‘{‘,”).replace(‘}’,”)”

This will display the name of the memcached statistic along with its value and will allow you to hand pick the OIDs that you want to track. Yes, I know it could be done simpler with translate instead of multiple replace. Left as an exercise for the Python-aware reader.

2. after having a complete list of OIDs use this one-liner:

/usr/bin/python -c “import memcache; print ‘##’.join(memcache.Client(['127.0.0.1:11211'], debug=0).get_stats()[0][1].values()).replace(‘##’,'n’)”

The memcached statistics will be displayed in the same order, but only their values not their names.

And this is the mandatory eye candy: