Postgresql in Ubuntu distribution

Ubuntu has default limitation for shared memory about 32 MB. This is why (I guess) packaged Postgres has shared_buffers parameter set to modest 24 MB.

This is quite low value for a large DB and for modern hardware. There are numerous recommendations on how big this value should be. It makes sense to try setting this value and run your benchmarks.

To increase kernel shared memory limitation edit /etc/sysctl.conf and add or replace the following (about 110 MB in this example):

kernel.shmmax = 110000000

Then run

sudo sysctl -p

to make the settings be effective immediately.

UTC datetime to UNIX timestamp

UNIX timestamp is somewhat reliable value which does not depend on timezone or daylight saving time.

There are number of posts in the "Internets" on how to convert timestamp to datetime. But all of them are either mistaken or consider converting timestamp to local timezoned datetime object.

The correct (and awfully akward) mean to convert timestamp to UTC datetime object:

from datetime import datetime
from time import mktime, timezone

def utcdatetime_to_ts(dt):
   return mktime(dt.utctimetuple()) - timezone

Then you can always:

assert utcdatetime_to_ts(datetime.utcnow()) - time() <= 1

Check also a better and shorter version in the comments.

Hosting migration story

While our code develops and user base grows, we need to adjust our server hardware to be cheap and powerful enough to handle the load. Here is the timeline:

• up to autumn 2008: Amazon EC2, small instance: 0.5 cores, 1.7 GB RAM
• up to Jan 2009: Gandi.net: 1..2 cores, 1..2 GB RAM
• up to Apr 2009: Serverloft.com L server: 4 cores, 4 GB RAM
• since Apr 2009: Serverloft.com XL server: 4*2 cores, 8 GB RAM

While cloud solutions like EC2 and Gandi.net provide a great deal of flexibility, for us it is still cheaper to stick with traditional dedicated server. Serverloft, while being DS provider, still allows many features previously available only for VDS users: OS reinstall and hard reboot - via WEB interface.