OR query in Solr not working - solr

Question

My Solr server seems only working with AND but not OR, e.g.
/solr/select?q=(marsden AND emma)&qt=yodl_handler works, but
/solr/select?q=(marsden OR mackey)&qt=yodl_handler doesn't.
For each individual query, it returns resutls, e.g.
/solr/select?q=marsden&qt=yodl_handler returns 2 results
/solr/select?q=mackey&qt=yodl_handler returns 3 results
Any suggestions are appreciated!
Here is the definition of yodl_handler:
<requestHandler name="yodl_handler" class="solr.DisMaxRequestHandler">
<lst name="defaults">
<str name="echoParams">explicit</str>
<float name="tie">0.01</float>
<str name="qf">
dc.title^1 dc3.title^1 dc.type^1 vra2.logical.creator^1 vra2.image.agent.name^1 vra2.image.agent.role^1 vra2.image.agent.role^1 vra2.image.location.name^1 vra2.image.rights.rightsholder^1 vra2.image.source.refid^1 vra2.image.title^1 vra2.image.worktype^1 vra2.work.agent.attribution^1 vra2.work.agent.name^1 vra2.work.agent.role^1 vra2.work.culturalContext^1 vra2.work.description^1 vra2.work.location-type^1 vra2.logical.location.place^1 vra2.logical.location.name^1 vra2.work.location.refid^1 vra2.work.material^1 vra2.work.rights.rightsHolder^1 vra2.work.StylePeriod^1 vra2.work.subject.term.name^1 vra2.work.subject.term.place^1 vra2.work.subject.term.keyword^1 vra2.work.technique^1 vra2.work.title^1 vra2.work.worktype^1 iris2.instrument.instrumentType^1 iris2.instrument.primaryInstrumentType^1 iris2.instrument.secondaryInstrumentType^1 iris2.instrument.instrumentType.alltypes^1 iris2.instrument.author^1 iris2.references.allauthors^1 iris2.instrument.researchArea^1 iris2.instrument.typeOfFile^1 iris2.instrument.software^1 iris2.instrument.dataType^1 iris2.instrument.linguisticTarget^1 iris2.instrument.sourceLanguage^1 iris2.instrument.funder^1 iris2.instrument.licence^1 iris2.participants.participantType^1 iris2.participants.firstLanguage^1 iris2.participants.targetLanguage^1 iris2.participants.gender^1 iris2.participants.proficiencyLearner^1 iris2.participants.proficiencyStudentsTaught^1 iris2.participants.yearsOfTeachingExperience^1 iris2.participants.domainOfUse^1 iris2.references.publicationType^1 iris2.references.author^1 iris2.references.author.lastnames^1 iris2.references.booktitle^1 iris2.references.journal^1 iris2.references.publicationDate^1 iris2.references.publicationLatestDate^1 iris2.references.publisher^1 iris2.references.placeOfPublication^1 iris2.references.editor^1 iris2.references.conferenceName^1
</str>
<int name="ps">100</int>
<str name="q.alt">*:*</str>
<str name="hl.fl">text features name</str>
<str name="f.name.hl.fragsize">0</str>
<str name="f.name.hl.alternateField">name</str>
<str name="f.text.hl.fragmenter">regex</str>
</lst>
</requestHandler>

Answer 1

The simple answer is, the Solr DisMax query parser does not support boolean logic in queries. The appearance of it working with the query involving "AND" is probably a side-effect of the way your fields are indexed (stop words?) or appears in the underlying data.
You can get a better idea what's happening under the hood if you send the debugQuery parameter, e.g.:
/solr/select?q=(marsden AND emma)&qt=yodl_handler&debugQuery=true
There's further documentation on the Solr wiki about the Dismax parser:
The Dismax query parser supports an extremely simplified subset of the Lucene QueryParser syntax. Quotes can be used to group phrases, and +/- can be used to denote mandatory and optional clauses ... but all other Lucene query parser special characters are escaped to simplify the user experience. (see DisMaxQParserPlugin)
The good news is, if you're using a modern version of Solr (3.1+), you have access to the new ExtendedDisMax parser, which DOES support boolean queries. `