In which situations is TokuDB higher performance? I noticed that WordPress runs quite a bit faster when I use XtraDB (MariaDB's InnoDB replacement) instead of TokuDB. This is strange, because TokuDB is advertised as being 20x faster.

However, I noticed that YOURLS stat pages are a tiny bit faster when I use TokuDB for the gigantic (~22,000 rows) log table.

So the question is: What situations will TokuDB be a higher-performance database engine than others, such as XtraDB/InnoDB?
Unless your WordPress site is huge, you are unlikely to see much performance improvement in switching to TokuDB, if any at all. TokuDB's 20x performance advantage is for an indexed insertion workload, where the secondary indexes do not fit in memory.

You will be using less space on disk with TokuDB's compression.