Functionality of Sizeclass column in Dictionary (sys_dictionary) tableSummaryThis article describes what sizeclass field is and what is it used for. The Sizeclass (sizeclass) is an integer column part of the Dictionary (sys_dictionary) table.It is used to store a row count for the tables defined in the instance. That means in the Dictionary (sys_dictionary) it will show a value only under the records that have a Type of Collection.The row count value from sizeclass is used internally by ServiceNow APIs when modifying tables structure (for example adding/removing a column, creating an index, etc).The row count values are calculated using the following logic: If table has less than 1 million records the platform will run a query on the logical/physical table to get the row countIf the table has more than 1 million records, the platform will get an estimated row count from the table statistics provided by the storage engine (database).Note: Tables like for example incident, problem, change_request, sc_request are considered logical tables since they all extend from task table. Based on point a. task table is considered to be a physical table Based on a. and b. for tables over 1 million rows we will actually store the row count value of the root parent table, and in the example of incident table we will store the estimated row count from task table. The row count values are updated daily by default via a scheduled job called Collect Table Stats. General recommendations: - if an accurate row count is needed at a certain moment in time for a certain table, use GlideAggregate with a COUNT aggregation rather than GlideRecord.getRowCount(). The GlideRecord.getRowCount() works by getting the whole result set without using the build-in aggregation functions of the database (like COUNT). - do not run very frequently GlideAggregate with a COUNT on very large tables without additional filters as it can have a performance impact (SELECT COUNT(*) FROM table can take time on tables with 10ths or 100s of millions of records) on the database