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The global search index is configured in the above-mentioned configuration file
(repository-configuration.xml which can be found in various locations)
in the query-handler tag.
<query-handler class="org.exoplatform.services.jcr.impl.core.query.lucene.SearchIndex">
In fact, when using Lucene, you should always use the same
analyzer for indexing and for querying, otherwise the results are
unpredictable. You do not have to worry about this, JCR does this for
you automatically. If you do not like the StandardAnalyzer to be configured by
default, just replace it with your own.
If you do not have a handy QueryHandler, you can learn about how to create a customized QueryHandler in the Query Handler configuration section.