Use case

In some extremely large workloads (trillions of rows) primary index may take significant amount of memory: tens or hundreds of GBs. Instead we can use cache for primary similar to mark cache instead of always storing index for parts.

Describe the solution you'd like

Use a cache similar to mark cache. If lazy load and primary index cache are enabled store index in that cache instead of storing it in data part.

Describe alternatives you've considered

Lazy load of index, but the problem is that index is never evicted and once primary index was analyzed for some query the index will be stored in memory until restart or SYSTEM UNLOAD PRIMARY KEY query.