Oh, solr home – where art thou

Ever started a Solr (5.x) with an example, stopped it and then could not figure out where that example actually lives? I certainly have.

This did not used to be a problem in Solr 4.x because you started the instance manually and were forced to know where your Solr home directory was (with solr.solr.home property). And they were all in the example directory out of the box anyway. But with Solr 5, we now have startup scripts, examples, and startup configurations which make things easier to get going, but may also introduce some confusion down the road.

So, this is a compilation of all the examples Solr 5.3 ships with, what configs they are using and where the startup scripts create homes for them. Plus a couple of weird related things.

Let’s start from starter configurations. Every Solr collection has one, and several examples use the same configuration.

Solr ships with three configurations, you can see the list if you run bin/solr create_core -help. Those configurations are:

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Solr gotchas – core swapping

Apache Solr allows to swap two cores around for non-Cloud configurations. They take each other’s name, so it is a good way to push an updated core into a production without downtime.

But an interesting question is how this is achieved. Normally, core name is it’s directory name too. So, does Solr rename the directory on the filesystem too?

Not really! Instead name property in the core.properties file is updated to use the name of the other core.  Usually that property is used to give an alternave name of the core for when the directory naming conventions are not suitable.

The gotcha is – of course – that you still have two directories with right looking names for the cores you see in the Admin UI. So, it is very easy to forget that extra redirection/rename step when troubleshooting somebody else’s – or even your own old – setup.

Comparing Solr and Elasticsearch – My presentation

I presented at the Lucene/Solr Revolution 2014 in November, comparing Solr and Elasticsearch. The target audience was a technical person who wants to understand how similar (mostly Lucene) concepts are expressed in these two products.

The presentation was only 30 minutes, so I could not go into the subject as deep as I initially hoped. But the room was more than full and people came up to me afterwards saying that they really liked the comparison and found it helpful.

The slides are available already and the video should hopefully be out soon as well.

> From inner thoughts to outer limits of Alexandre Rafalovitch