Pick one and press Start, then click Next › to step through it.
The cached load tracking the write rate instead of the read rate, and the crossover landing where writes catch up to reads.
That a cache sells reuse: it pays only while an entry is read again before a write invalidates it, which the read-to-write ratio decides.
Count the database load with no cache and with one, then drag the write rate up until the reuse collapses and the cache stops paying.