Functionality of Sizeclass cloumn in sys_dictionary tableSummarySize class column is applicable for collection records in sys_dictionary tableIt stores the number of records in a particular table.However there are exceptions to this , as mentioned in 4th point below.The number of records in that table calculated from time to time by a scheduled job "Collect Table Stats" which runs once a day. As per the code , the threshold value is set to 1 million. Whenever the record count on a table is more than that , the total count is calculated based on the actual storage/physical table. Eg - in case of incident , when the total count of incident is more than 1 million , it will calculate the total size of the task table.This is because although logical tables such as incident, sc_task, problem, and change_request are distinct in the application layer, they ultimately operate on a shared physical storage table—namely, task table. Note - For large tables such as task ,it gives an estimated count from the storage table. This is to avoid any performance issues while doing a COUNT(*) on large tables.