[xwiki-devs] [VOTE] Introduce a cache of documents used in the current request

Hi devs, Currently the getDocument method always goes to the storage to retrieve the document, even if the same document has just been retrieved. This means that the following code will not work: #set($d = $xwiki.getDocument('X')) $d.setTitle('the title') $xwiki.getDocument('X').getTitle() # will not print 'the title' I'd like to change getDocument so that it first searches in a map of used documents in the current context. This means the following: - getDocument searches in XWikiContext.usedDocuments (or better, in the ExecutionContext) - if found, return the value from there - if not, go to the storage, return it to the caller - when the document is changed for the first time, i.e. when api.Document.getDoc() is called, clone the original document and put it in usedDocuments - as a special case, PreviewAction also puts the updated context document in usedDocuments This means that consecutive calls for retrieving a (changed) document will always return the same object. This prevents possible preview bugs, like http://jira.xwiki.org/jira/browse/XABLOG-14 or http://jira.xwiki.org/jira/browse/XWIKI-4689 Yet this is an important behavior change. Do you think anybody is using this "feature", and actually expects the above code example to work as it does now? Also, we must be careful with the performance, since this new map could get big, holding all the documents in the database. Perhaps a LRU fixed-size map would be better, although this breaks the uniqueness guarantee. So, WDYT? 1. Should we introduce this cache? 2. Should it be limited in size? -- Sergiu Dumitriu http://purl.org/net/sergiu/