Apache Solr Reference Guide Covering Apache Solr 6.0

class
enabled
The class to use for logging. The corresponding JAR file must be available to solr, perhaps
through a directive in solrconfig.xml.
true/false - whether to enable logging or not.
The element
size
Node
threshold
The number of log events that are buffered.
Description
The logging level above which your particular logging implementation will record. For example
when using log4j one might specify DEBUG, WARN, INFO, etc.
The element
Custom shard handlers can be defined in solr.xml if you wish to create a custom shard handler.
Since this is a custom shard handler, sub-elements are specific to the implementation.
Substituting JVM System Properties in solr.xml
Solr supports variable substitution of JVM system property values in solr.xml, which allows runtime
specification of various configuration options. The syntax is ${propertyname[:option default value] }.
This allows defining a default that can be overridden when Solr is launched. If a default value is not specified,
then the property must be specified at runtime or the solr.xml file will generate an error when parsed.
Any JVM system properties usually specified using the -D flag when starting the JVM, can be used as variables
in the solr.xml file.
For example, in the solr.xml file shown below, the socketTimeout and connTimeout values are each set
to "0". However, if you start Solr using ' bin/solr -DsocketTimeout=1000', the socketTimeout option of
the HttpShardHandlerFactory to be overridden using a value of 1000ms, while the connTimeout option
will continue to use the default property value of "0".
${socketTimeout:0}
${connTimeout:0}
Defining core.properties
Core discovery means that creating a core is as simple as a core.properties file located on disk. The core.
properties file is a simple Java Properties file where each line is just a key=value pair, e.g., name=core1.
Notice that no quotes are required.
A minimal core.properties file looks like this (however, it can also be empty, see information on placement
of core.properties below):
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