They're just rows in a MySQL database. Traditional RDBMS for OLTP are built around the assumption that all data is mutable. An unscrupulous Wikipedia DBA could unilaterally delete new history rows before anyone downloads a hard-copy and then no-one would be the wiser.
On the topic of OLTP RDBMS: things are changing though: ISO SQL (and at least MS SQL Server) have added support for "LEDGER" tables that extend the Temporal Table system (...that we know and love...er...hate) with immutability secured with cryptographic keys. Basically, you get to have your own centralized blockchain-like table.... so long as you trust your DBMS (and DBA) with the keys.
There's two types: append-only and updatable (which is still append-only under-the-hood, as destructive DML operations are still just appended to current history, just like with git).
It's pretty cool, I'll admit - I've been wanting support for true "read-only" tables for ages - the only thing I'm dreading is having to put-up with poor tooling support for a decade or two (e.g. Entity Framework Core still doesn't support temporal-tables, and SQL Server still only supports SYSTEM versioning and not the (far more useful) APPLICATION versioning system, argh).
That said, I don't think Wikipedia would really want crypto-signed page edit histories: it would obligate them to host truly objectionable content (otherwise the hash references would break), and there's far too many sociopathic griefers online for that to not happen...
I believe they do; you can download archives at [0].
It mentions that the edit history can be downloaded by looking for dumps with page-meta-history in their name at [1]
The same is probably true for OpenStreetMap et al.
On the topic of OLTP RDBMS: things are changing though: ISO SQL (and at least MS SQL Server) have added support for "LEDGER" tables that extend the Temporal Table system (...that we know and love...er...hate) with immutability secured with cryptographic keys. Basically, you get to have your own centralized blockchain-like table.... so long as you trust your DBMS (and DBA) with the keys.
There's two types: append-only and updatable (which is still append-only under-the-hood, as destructive DML operations are still just appended to current history, just like with git).
https://docs.microsoft.com/en-us/azure/azure-sql/database/le...
https://docs.microsoft.com/en-us/azure/azure-sql/database/le...
It's pretty cool, I'll admit - I've been wanting support for true "read-only" tables for ages - the only thing I'm dreading is having to put-up with poor tooling support for a decade or two (e.g. Entity Framework Core still doesn't support temporal-tables, and SQL Server still only supports SYSTEM versioning and not the (far more useful) APPLICATION versioning system, argh).
That said, I don't think Wikipedia would really want crypto-signed page edit histories: it would obligate them to host truly objectionable content (otherwise the hash references would break), and there's far too many sociopathic griefers online for that to not happen...