the explain part are different in solr4.7 and solr 5.3.1. In solr 4.7,
there is only one line
<lst name="explain">
<str name="36652255">1.0 = (MATCH) MatchAllDocsQuery, product of:
1.0 = queryNorm</str>
<str name="36651884">1.0 = (MATCH) MatchAllDocsQuery, product of:
1.0 = queryNorm</str>
</lst>
in solr 5.3.1, there is actually a boost, and the score is product of boost
& queryNorm.
Can that cause the problem? if solr5 need to calculate the product of all
the hits. I am not sure where the boost come from, and why it is different
in solr4.7
<lst name="explain">
<str name="36652255">1.0 = *:*, product of:
1.0 = boost
1.0 = queryNorm</str>
<str name="36651884">1.0 = *:*, product of:
1.0 = boost
1.0 = queryNorm</str>
</lst>
