The classic example of a changing workload is a database which has a normal workload that maybe resembles a zipf or bell distribution but then someone runs exports which do full scans over large parts of the DB. These changes in workloads can be intermittent but they exist. A very similar change in workload that is well known is the pagecache for filesystems (e.g. backup doing full scan over disk and evicting everything from the cache) which is why admission policies were invented in the first place. So you have two different algorithms already. Just maybe not adaptive.
A friend of mine works on a online-shop / distribution system that during most of the day has a zipf like distribution but after normal working hours when retail shops close he gets completely different patterns as the shops push their data for the day into the system and then all kinds of BI tools run for a few hours.
Of course adaptive caches are never completely optimal because it takes time for them to learn which workload is actually currently happening but after a while they can get very close. A good adaptive cache should not need tuning to get good results because the whole reason for it to be adaptive is to tune itself. Of course there are quite a few adaptive caches, especially the first ones that pioneered this, that still needed tuning.
I don't understand the last question. You say you can't see how FIFO can fail catastrophically and at the same time state a case how it can. Scanning workloads are something that does show up in the real world all the time. NovaX seems to have run your algorithm through some traces where it had a near zero hitrate. It can be more important to avoid these extreme cases than having a slightly better hitrate in the normal case.
A friend of mine works on a online-shop / distribution system that during most of the day has a zipf like distribution but after normal working hours when retail shops close he gets completely different patterns as the shops push their data for the day into the system and then all kinds of BI tools run for a few hours.
Of course adaptive caches are never completely optimal because it takes time for them to learn which workload is actually currently happening but after a while they can get very close. A good adaptive cache should not need tuning to get good results because the whole reason for it to be adaptive is to tune itself. Of course there are quite a few adaptive caches, especially the first ones that pioneered this, that still needed tuning.
I don't understand the last question. You say you can't see how FIFO can fail catastrophically and at the same time state a case how it can. Scanning workloads are something that does show up in the real world all the time. NovaX seems to have run your algorithm through some traces where it had a near zero hitrate. It can be more important to avoid these extreme cases than having a slightly better hitrate in the normal case.