Adding custom fields to packets in ndnSIM 2.3 without forking the entire repository.

The recommended way to build something on top of ndnSIM is to fork its scenario template repository and work inside there. You still need to download and compile the actual framework, however you will simply install it into /usr/local and link to it instead of actually working inside the main repository.

It turns out that this workflow actually makes certain tasks a lot more difficult. You might think a network simulator would make it easy to add new header fields to packets. Well, think again.

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An idiot's guide to fulltext search in PostgreSQL.

I love PostgreSQL. It’s probably the most powerful open-source database system out there. Recent features to handle JSON and geospatial data are allowing it to supplant specialized database systems and become closer to a one-DB-fits-all solution. One feature that I’ve recently been able to exploit is its fulltext search engine. It allowed me to easily move from a terrible search implementation (using regular expressions) to one that actually meets users’ expectations.

In this article, I will walk through a basic fulltext search configuration, as well as highlight a few potential improvements that can be made if you’re so inclined.

Many of the features discussed in this post are only available as of PostgreSQL 9.6. Earlier versions have some rudimentary fulltext functionality, but a lot of the more powerful tools we’ll be using are fairly new.

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Fun with integer division optimizations.

I recently stumbled across a post about some crazy optimization that clang does to divisions by a constant. If you aren’t interested in reading it yourself, the summary is as follows:

  • Arbitrary integer division is slow.
  • Division by powers of 2 is fast.
  • Given a divisor \(n\), the compiler finds some \(a, b\) such that \(a/2^b\) approximates \(1/n\).
  • This approximation gives exact results for any 32-bit integer.

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The problem with Python's datetime class.

This might sound like a strong opinion, but I’m just going to put it out there: Python should make tzinfo mandatory on all datetime objects.

To be fair, that’s just an overzealous suggestion prompted by my frustration after spending two full days debugging timestamp misbehaviors. There are plenty of practical reasons to keep timezone-agnostic datetimes around. Some projects will never need timestamp localization, and requiring them to use tzinfo everywhere will only needlessly complicate things. However, if you think you might ever need to deal with timezones in your application, then you must plan to deal with them from the start. My real proposition is that a team should assess its needs and set internal standards regarding the use of timestamps before beginning a project. That’s more reasonable, I think.

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Using bcache to back a SSD with a HDD on Ubuntu.

Recently, another student asked me to set up a PostgreSQL instance that they could use for some data mining. I initially put the instance on a HDD, but the dataset was quite large and the import was incredibly slow. I installed the only SSD I had available (120 GB), and it sped up the import for the first few tables. However, this turned out to not be enough space.

I did not want to move the database permanently back to the HDD, as this would mean slow I/O. I also was not about to go buy another SSD. I had heard of bcache, a Linux kernel module that lets a SSD act as a cache for a larger HDD. This seemed like the most appropriate solution – most of the data would fit in the SSD, but the backing HDD would be necessary for the rest of it. This article explains how to set up a bcache instance in this scenario. This tutorial is written for Ubuntu Desktop 16.04.1 (Xenial), but it likely applies to more recent versions as well as Ubuntu Server.

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