In-memory content cache decreases performance on YCSB workloadc

Nobody has claimed this yet.

Related: https://github.com/losfair/mvsqlite/pull/92

It is strange that enabling content cache causes performance decrease over time: (this is with a hot cache that has almost all pages)

```
READ - Takes(s): 10.0, Count: 103349, OPS: 10344.3, Avg(us): 6159, Min(us): 1108, Max(us): 51167, 99th(us): 11775, 99.9th(us): 48703, 99.99th(us): 50719
...
READ - Takes(s): 160.0, Count: 1057188, OPS: 6607.8, Avg(us): 9661, Min(us): 797, Max(us): 55519, 99th(us): 50719, 99.9th(us): 53823, 99.99th(us): 55199
```

while on the same cluster, with content cache disabled:

```
READ - Takes(s): 190.0, Count: 1730079, OPS: 9106.2, Avg(us): 7006, Min(us): 809, Max(us): 51423, 99th(us): 12815, 99.9th(us): 47007, 99.99th(us): 50847
```

Start by reviewing the related pull request 92 and the YCSB workload results in this issue, then locate the in-memory content-cache implementation. Reproduce the comparison with the cache enabled and disabled; done means identifying and correcting the cache-related performance regression and verifying the workload improves.

Written by the indexing model from the issue text.