[solr] solr Similarity:切换不同相似度计算方法

Similarity改变solr的打分机制；

solr本身已经提供了几种算法

org.apache.solr.search.similarities.BM25SimilarityFactory org.apache.solr.search.similarities.DefaultSimilarityFactory org.apache.solr.search.similarities.DFRSimilarityFactory org.apache.solr.search.similarities.IBSimilarityFactory org.apache.solr.search.similarities.LMDirichletSimilarityFactory org.apache.solr.search.similarities.LMJelinekMercerSimilarityFactory org.apache.solr.search.similarities.SchemaSimilarityFactory

可以在managed-schema下面添加：

<similarity class="org.apache.solr.search.similarities.SchemaSimilarityFactory"/>

<similarity class="org.apache.solr.search.similarities.BM25SimilarityFactory"/>

<similarity class="org.apache.solr.search.similarities.DefaultSimilarityFactory"/>

.....

测试会发现不同相似度计算方法检索上的差异：