Task #52304: Performance issues
Page cache saves the hash_base
The hash_base (the array from which the cache hash is calculated) is saved into the cache. But this isn't required IMHO, it will be read on every cached request but doesn't get processed somewhere (as I read the source).
So if we remove it, it won't get saved and loaded, which reduces bandwidth to the SQL server and reduces the string which needs to be un-/serialized.