For read only btree, there is no need to instantiate the updates, such as tombstones and prepared updates, onto the update chain as we cannot modify it. If we still instantiate the prepared updates, for layered tables, we may get prepare conflict errors even if the prepared updates have been resolved. It also helps saving cache space on the standby for the disaggregated storage architecture.

Along with the change, we should also change the visibility checking function for the onpage value. Instead of always return not visible for prepared onpage value, we may need to return prepare conflict sometims.