Search is an important part of any web app like a wiki, but search is harder than it looks — especially in a multilingual environment. MediaWiki has to support not just your standard Western languages like English and Spanish, but many more with special requirements:
- Some can be written in multiple scripts (such as Serbian in Cyrillic or Latin), and searches should match text written either way.
- Some languages don’t use word spacing, like Chinese and Japanese. To let the search index know where word boundaries are, we have to internally insert spaces between some characters:
维基百科 -> 维 基 百 科
Then to add insult to injury, we need to fudge the Unicode characters to ensure things work reliably with older and newer versions of MySQL:
维 基 百 科 -> u8e7bbb4 u8e59fba u8e799be u8e7a791
For a long time, this word segmentation wasn’t being handled correctly for Chinese in our default MySQL search backend, so searching for a multi-character word often gave false matches where the characters were all present, but not together.
This is now fixed for MediaWiki 1.16; the intermediate query representation passed to the search backend now internally treats your multi-character Chinese input as a phrase, which will only match actual adjacent characters:
维基百科 -> +”u8e7bbb4 u8e59fba u8e799be u8e7a791″
Note that Wikimedia’s sites such as Wikipedia run on a fancier, but more demanding, search backend with a separate Java-based engine built around Apache Lucene. Sometimes we have to remind ourselves that third-party users will mostly be using the MySQL-based default, and oh boy it still needs some lovin’! :)