Updated: June 11th, 2015

The Problem

I am throwing up a quick post about a relatively cryptic error that Solr started throwing the other day here at Plaxo. After happily running for a few days, I suddenly started getting pages about failed Solr indexing.

Upon closer examination, I saw the following repeatedly in the log file:

catalina.2009-09-18.log:SEVERE: java.io.IOException: directory 'DATADIR/index'
exists and is a directory, but cannot be listed: list() returned null

I tried to see if sending an OPTIMIZE command would help but the server returned the same response.

Digging Deeper

The reason was these errors was quite simple – Solr was running into the system level limit on allowed number of open files (ulimit). This limit can be seen by running


Updated: September 8th, 2009

image Well, it looks like the wait is over. I have been waiting for almost 5 years for a new phone that is good enough to make the switch from Samsung A900 (which has free tethering). Don't even get me started on the iPhone and its outrageous monopoly with AT&T. Android and the growing multitude of devices running it is, however, completely different business. Android offers unparallel freedom and I truly believe it will be the top phone OS within a few years as more and more Android phones are introduced to the market.

But where was I? I have been closely following Android news since its inception, then the introduction of the first phone – T-Mobile G1 (aka HTC Dream), …


Updated: June 11th, 2015

In the past few weeks I've been implementing advanced search at Plaxo, working quite closely with Solr enterprise search server. Today, I saw this relatively detailed comparison between Solr and its main competitor Sphinx (full credit goes to StackOverflow user mausch who had been using Solr for the past 2 years). For those still confused, Solr and Sphinx are similar to MySQL FULLTEXT search, or for those even more confused, think Google (yeah, this is a bit of a stretch, I know).


  • Both Solr and Sphinx satisfy all of your requirements. They're fast and designed to index and search large bodies of data efficiently.
  • Both have a long list of high-traffic sites using them (Solr, Sphinx