SOLR: Improve relevancy by boosting exact and phrase match

Once we have the index ready for searching, the next implicit step is to improve the relevancy of the search index. SOLR of course provides ways to tune the search relevancy but one very obvious way to improve your relevancy almost always gets ignored. By boosting exact and phrase matching over the query matching we can achieve relevancy improvement by significant factor.

Exact Match Setup

To set a field(s) for exact matching, add another field in the Schema.xml and copy the content into it using copyField

<field name="title" type="text" indexed="true" stored="true" /> <field name="titleExact" type="textExact" indexed="true" stored="true" /> <copyField source="title" dest="titleExact"/>

You would notice that the data type for titleExact is set to "textExact" (defined below), although similar exact match effect can be achieved by setting the datatype to "string" but with adding our own datatype we can further fine tune by adding appropriate tokenizer and filters.

<fieldType name="textExact" class="solr.TextField" positionIncrementGap="100" >    <analyzer type="index">    <tokenizer class="solr.WhitespaceTokenizerFactory"/>    <filter class="solr.LimitTokenCountFilterFactory" maxTokenCount="20"/>    <filter class="solr.LowerCaseFilterFactory"/> </analyzer> <analyzer type="query">    <tokenizer class="solr.WhitespaceTokenizerFactory"/>    <filter class="solr.LimitTokenCountFilterFactory" maxTokenCount="20"/>    <filter class="solr.LowerCaseFilterFactory"/> </analyzer>

Here I have used WhiteSpaceTokenizer without stopwords or stemming filters. I am using LimitTokenCounterFilter to limit the number of tokens and LowerCaseFilter to make the matching case-insensitive. We can further fine tune the textExact dataType to make the exact match a bit more lenient or strict per our use case.

Putting it All Together

Now to boost the exact match field and phrase matching, in the SolrConfig.xml -

<str name="qf">title titleExact^10</str> <str name="pf">title^10 titleExact^100</str>

Now for both query and phrase matching we are boosting the exact matching field "titleExact" match higher than the non-exact matching field "title", also the same fields are boosted higher for phrase search (pf) compare to query or keyword search (qf). This would be a simple and first step to improving relevancy.