Avoid slow highlighting on Solr because of stemming

I am quite new about using Solr, but would like to ask your help. I am developing an application which should be able to highlight the results of a query. For this I am using regex fragmenter:

<highlighting>
<fragmenter name="regex" class="org.apache.solr.highlight.RegexFragmenter">
<lst name="defaults">
  <int name="hl.fragsize">500</int>
  <float name="hl.regex.slop">0.5</float>
  <str name="hl.pre"><![CDATA[<b>]]></str>
  <str name="hl.post"><![CDATA[</b>]]></str>
  <str name="hl.useFastVectorHighlighter">true</str>
  <str name="hl.regex.pattern">[-\w ,/\n\"']{20,300}[.?!]</str>
  <str name="hl.fl">dokumentum_syn_query</str>
</lst>

The field is indexed with term vectors and offsets:

<field name="dokumentum_syn_query" type="huntext_syn" indexed="true" stored="true"   multiValued="true" termVectors="on" termPositions="on"  termOffsets="on"/>
<fieldType name="huntext_syn" class="solr.TextField" stored="true" indexed="true" positionIncrementGap="100">
      <analyzer type="index">
        <tokenizer class="com.morphologic.solr.huntoken.HunTokenizerFactory"/>
        <filter class="solr.StopFilterFactory" ignoreCase="true" words="stopwords_query.txt" enablePositionIncrements="true" />
        <filter class="com.morphologic.solr.hunstem.HumorStemFilterFactory"
        lex="/home/oroszgy/workspace/morpho/solrplugins/data/lex"
        cache="alma"/>
        <filter class="solr.LowerCaseFilterFactory"/>
      </analyzer>
        <analyzer type="query">
          <tokenizer class="solr.StandardTokenizerFactory"/>
      <filter class="solr.StopFilterFactory" ignoreCase="true" words="stopwords_query.txt" enablePositionIncrements="true" />
      <filter class="com.morphologic.solr.hunstem.HumorStemFilterFactory"
        lex="/home/oroszgy/workspace/morpho/solrplugins/data/lex"
        cache="alma"/>
          <filter class="solr.SynonymFilterFactory" synonyms="synonyms_query.txt" ignoreCase="true" expand="true"/>
        <filter class="solr.LowerCaseFilterFactory"/>
      </analyzer>
</fieldType>

The highlighting works well, excepts that its really slow. I realized that this is because the highlighter/fragmenter does stemming for all the result documents again.

Could you please help me why does it happen an how should I avoid this? (I thought that using fastvectorhighlighter will solve my problem, but it didn't)

The problem was, that I tried to use values "on" instead of "true". So the proper line on the schem is:

    <field name="dokumentum_syn_query" type="huntext_syn" indexed="true" stored="true"   multiValued="true" termVectors="true" termPositions="true"  termOffsets="true"/>

to avoid "slow" solr results by highlighting, i decided not to use the solr highlighting. I coded the highlighting functionality on client-side. That work's for me, but is ab bit tricky, because you have to handle the search-phrase at client side in the same way solr does on server side in order to find also the tokenized and stemmed terms on client-side - to mark, what solr was searched for and found. That means: you have to implement stemming functionality on client side.

Alternative:

I think, the term vector in the result sets gives you information about position of the term you have to highlight on the client side. You could use those information to highlight the terms on client side without implement stemmer on client. But i think: finally this is not really an alternative. Because Solr still needs to compute the position of the words - so you will not save time on server side.