Interwiki integration

This page is for proposing and discussing interwiki integration ideas. These ideas seek to fix the following bugs, while also enabling more interconnection among the wikis of the wikisphere as a whole, in ways not contemplated by these bugs:

Bug	Description
11	Red interwiki links -- check for page existence across wikis
708	Interproject links
1066	Cross-wiki talk page notification
1837	Search all wikis at once
3525	Cross-wiki watchlists
3544	Single recent changes on several MediaWikis
9890	Reasonably efficient interwiki transclusion
11423	Central database for interwiki
14234	Create a way to change home wiki in CentralAuth
15607	Implement the Interlanguage extension in Wikipedia
16568	Create a hub devoted to cross-wiki data exchange
23741	Resolve searchNs collisions on wiki farms with a shared user table
23999	Provide method to store API/DB information for interwiki sites
27696	It should be possible to see the changes to the interwiki page in the watchlist

Create wikispaces and langspaces in central database

Create a central database/website as a clearinghouse for interwiki data sharing. Have local wikis retrieve data from it (e.g. for producing interwiki watchlists, recentchanges, and existence-detecting links) via the backend, and allow remote wikis to either (1) pull data from it or (2) subscribe to a service in which the clearinghouse website will periodically push updates to those remote wikis via their APIs. The shared central database will contain wikispace and langspace fields, in addition to the already-supported namespace fields, in the appropriate tables. Pages would be accessible as follows:

Wikispace	Langspace	Namespace	Page title	Result
Wikipedia	English	Portal	Geography	wikipedia:en:Portal:Geography
Wiktionary	French	Main	Fromage	wiktionary:fr:fromage
...	...	...	...	...

This will enable both existence-detecting links to "absolute" addresses (e.g. http://wikimedia.org/wiki/wikipedia:en:Portal:Geography ) and (as is already the case) to "relative addresses" (e.g. http://en.wikipedia.org/Portal:Geography ). As is already the case, users would not necessarily need to type in the full page title (including wikispace and langspace); if the user is on, say, enwiki and types in Portal:Geography, the software will assume he means wikipedia:en:Portal:Geography.

Implementation

Make necessary changes to dozens/hundreds of core and extension files. E.g. parameters will need to be added to many functions, and new variables will need to be added to many class objects. Many aspects of the user interface, including special pages and the API, will need to be revised to make use of the new fields. In the central database, add the following database fields, and implement the associated functionality to make use of them:

Table	WikiField	LangField
archive	ar_wikispace	ar_langspace
job	job_wikispace	job_langspace
logging	log_wikispace	log_langspace
pagelinks	pl_wikispace	pl_langspace
protected_titles	pt_wikispace	pt_langspace
querycache	qc_wikispace	qc_langspace
querycache2	qcc_wikispace	qcc_langspace
recentchanges	rc_wikispace	rc_langspace
redirect	rd_wikispace	rd_langspace
templatelinks	tl_wikispace	tl_langspace
user_properties	up_wikispace	up_langspace
watchlist	wl_wikispace	wl_namespace

Advantages and disadvantages

Advantages

Allow for integrated watchlists, integrated RecentChanges, interwiki page existence detection, etc.
Allow one database query to be run on the entire wiki farm without the need to UNION or JOIN a bunch of different databases.

Disadvantages

Could be hard to implement, requiring hundreds of changes to the core and extensions.

Rejected ideas

There was an idea to consolidate all local wikis' databases into one big database with different wikispaces and langspaces: "All configuration settings will need to be unified for the one big wikifarm, which might require changing some of them to arrays in order to maintain customizability of individual wikis." This idea was rejected due to performance concerns related to the difficulty/impossibility of scaling such a huge database to a multi-server system, and the probable difficulty of getting the community to accept such an extensive revision of core code.