Data definition language (DDL) operations include CREATE, DROP, and ALTER.
DDL operations on a given table or index lock out all other readers and writers from any table being modified. This approach is crucial to the accuracy of query results. It ensures, for example, that a table column does not disappear from the database while you are selecting data from that column.
They cannot start while any other transaction is using the table or index they are modifying.
For example, if a user issues a SELECT on a table, the table is locked and cannot be altered until the user logs out, issues a SELECT on another table, or issues a ROLLBACK.
They include an automatic COMMIT on completion.
Existing transactions that try to use the table being modified receive an error. In other words, if you are accessing a table, and a DDL command changes that table, your command fails.
At any given time, only one of the commands CREATE DBSPACE, DROP DBSPACE, and CHECKPOINT can be executing in a database.