I am new user of Piwik but as I see when the stored information on the database it’s huge it gives much problems. So I think that if Piwik might use SQLite3 for storing information. All the data are stored on one file that can be downloaded very easely for backup purposes also you can modify the information with SQL comands.
Sqlite only supports a subset of the ALTER TABLE syntax. A Piwik scheme change could easily leave you with an orphaned version of Piwik.
That said, sqlite support might make our integration tests faster…
Please also note that SQLite3 is very slow and cannot handle huge datasets. Having everything in a single file also prevents you from accessing the database in parallel (like logging two visits at the same time…). SQLite3 simply doesn’t work in any analytics scenario.
SQLite3 is very fast, though huge data sets are not its specialty. It is multi-user though, and multiple users can simultaneously use Piwik. It has single-user concurrency in terms of writing, but that is generally very fast in any case. For smaller sites, the overhead of MySQL is very painful.