Wiki applications are becoming increasingly important for knowledge sharing between large numbers of users. To prevent against vandalism and recover from damaging edits, wiki applications need to maintain revision histories of all documents. Due to the large amounts of data and traffic, a Wiki application needs to store the data economically on disk and processes them efficiently. Current wiki data management systems make a trade-off between storage requirement and access time for document update and retrieval. We introduce a new data management system, Cosmos, to balance this trade-off. Keywords Version control systems, Wikis