When you start up Solr using the –e techproducts parameter, it loads the configuration files from /server/solr/configsets/sample_techproducts_configs. These configuration files are extremely well documented.

A Solr core's instance directory is laid out like this:

Solr's schema for the index is defined in schema.xml. It contains the index's fields within the <fields> element and then the field type definitions within the <types> element. You will observe that the names of the fields in the documents we added to Solr intuitively correspond to the sample schema. Aside from the fundamental parts of defining the fields, you might also notice the <copyField> elements, which copy an input field as provided to another field. There are various reasons for doing this, but they boil down to needing to index data in different ways for specific search purposes. You'll learn all that you could want to know about the schema in the next chapter.

Each Solr core's solrconfig.xml file contains lots of parameters that can be tweaked. At the moment, we're just going to take a peek at the request handlers, which are defined with the <requestHandler> elements. They make up about half of the file. In our first query, we didn't specify any request handler, so we got the default one:

<requestHandler name="/select" class="solr.SearchHandler>
  <!-- default values for query parameters can be specified, these will be overridden by parameters in the request
 -->
  <lst name="defaults">
    <str name="echoParams">explicit</str>
    <int name="rows">10</int>
    <str name="df">text</str>
  </lst>
  <!-- … many other comments … -->
</requestHandler>

Each HTTP request to Solr, including posting documents and searches, goes through a particular request handler. Handlers can be registered against certain URL paths by naming them with a leading /. When we uploaded the documents earlier, it went to the handler defined like this, in which /update is a relative URL path:

<requestHandler name="/update" class="solr.UpdateRequestHandler" />

Requests to Solr are nearly completely configurable through URL parameters or POST'ed form parameters. They can also be specified in the request handler definition within the <lst name="defaults"> element, such as how rows is set to 10 in the previously shown request handler. The well-documented file also explains how and when they can be added to appends, or invariants named lst blocks. This arrangement allows you to set up a request handler for a particular application that will be searching Solr, without forcing the application to specify all of its search parameters. More information on request handlers can be found in Chapter 5, Searching.