how search in wikipedia works?

I am a beginer in web technologies so sry if its a lame question.

Wikipedia and other such sites which host million of web pages. How search works in these pages. Do they store all 开发者_高级运维html pages in memory? if yes What are the possible data structure used to store all the html pages to store in-memory and do search among those so fast?

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Wikipedia uses the Lucene full text search engine. Another popular full text search engine is Sphinx.

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They have quite detailed descriptions of what exactly they got.

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Wikipedia: Web search
How Internet Search Engines Work How Search Engines Work (rather nice explanation)