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[Solr] How To Fix java.io.IOException: directory FOO exists and is a directory, but cannot be listed: list() returned null


Posted by Artem Russakovskii on September 21st, 2009 in Linux, Programming, Solr

Updated: September 28th, 2009

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…

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Comparison Between Solr And Sphinx Search Servers (Solr Vs Sphinx – Fight!)


Posted by Artem Russakovskii on September 3rd, 2009 in Databases, MySQL, Programming, Solr

Updated: August 8th, 2010

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).

Similarities

  • 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

…

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