Redundancy with Multiple Free Web Hosts

How to set up redundant databases for mediawiki on R1, R2, L1 and L2?

So far, I found following free database online:

-------------- Free Databases -------------- [R1] Allows Remote access; ocassional down time; unlikely to lose data allows cron jobs. [R2] Allows Remote access; ocassional down time; likely to lose data no cron jobs.

[L1] No remote access; ocassional down time; unlikely to lose data. No cron jobs. [L2] No remote access; ocassional down time; unlikely to lose data. no cron job. 10Mb database. [L3] No remote access; very likely to force payment. allow cron jobs.

[A2] Allow remote access; 5Mb; slow.

----------------------------- And free servers for scripts: ----------------------------- [Heroku] Allow remote access; 10k rows, only 15 concurrent connection; slow Can it do cron jobs? [openshift] free python hosting.

------------ Current Idea ------------ R1 and R2 can be master/slave databases. But then, what to do when R2 loses all data?

Can I setup multi-master on L1, with R1 also as a master? And do the same for L2?

Another thing is R1 and L1 can use postgres while R2 and L2 must be mySQL. Can I mix the different kinds of database?

R2 can only install mediawiki 1.16. Can I mix different versions of mediawiki?

Or, let the hamsters push the wheel? Like, everytime when a user click a link on L1, the wiki would have 1/10 of chance to compare its page with master's page, if a local table says that has not been done in 15 minutes?

---------------------- Possibly Related Posts ---------------------- 1. Export entire wiki as xml, and then import it to another wiki. Possibly with pywikipediabot. Can this work on database without remote access / cron job? [ http://wikimedia.7.x6.nabble.com/site-mirror-and-master-slave-question-td497... ]

2. No automatic failover [ http://wikimedia.7.x6.nabble.com/Database-redundancy-tt747314.html#a747317]

3. Multi-master setup eat people alive [ http://wikimedia.7.x6.nabble.com/How-Do-You-Deal-With-MySQL-Replication-tt62... ]

4. Distributed Semantic Mediawiki The push/pull feed seems not automatic. [https://github.com/momo54/DSMW/wiki/Manual]

5. Can an extension add wiki pages? [ http://wikimedia.7.x6.nabble.com/MediaWiki-l-Can-an-extension-automatically-... ]

Thank you for help and advices.