Mediawiki software when installed without extensions, with the default settings does not offer search capabilities. Installing the MWSearch extension does not do searches either since this extension only provides integration with the Lucene-search extension.
However the Lucene search extension is part of the MediaWiki cluster deployment. Many of it's design parameters are long standing bugs are a result of this privileged relationship
Besides Lucene search many other search solutions exist. For many projects standalone projects exist which produce better results than the built-in search however these do not get integrated into the cloud.