[solr] solr Similarity:切換不同相似度計算方法

Similarity改變solr的打分機制；

solr本身已經提供了幾種算法

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"/>

.....

測試會發現不同相似度計算方法檢索上的差異：