Adrian,
The first reason TO use mysqli that you might care
about (which was
told
to me by someone on #MediaWiki) is that mysqli_stmt is much faster and
much more secure than mysql_query (you don't need to escape the inputs
to mysqli_stmt). The API is supposedly better, but they seem equally
simple to me.
There are multiple issues with prepared statements.
First of all, we do lots of query building anyway, where we may hit
multiple different queries.
We would still have to prepare multiple statements even for same
tasks (counts of arguments are different, different nested options,
yadda yadda).
Usually if we can aggregate multiple similar queries into single one,
we do.
You would not get too much efficiency if you would prepare same
queries, therefore you would have to keep a cache of prepared
statements.
Another important point to note is that for long running operations
that issue multiple queries, you have to deallocate statements once
you won't use it again, otherwise they will accumulate on server (and
leak memory).
As for security, our query builder solves it all \o/.
The only reason *I* would like to see mysqli supported
(even if it was
not the default method) would be so we could use mysqli_embedded.
mysqli_embedded allows people to use MediaWiki in standalone
applications much easier. In fact, it would allow people to use
MediaWiki without significant change in a wikipedia-on-dvd type
situation.
It's trivial to extend MediaWiki if only thing you wish is DB API
change. :)
Domas