It is finally solved for a few months, and I have written a program before, and the 20 threads call the database at the same time, but only one database connection is established. The result is old unstable, and running without reacting, and The call stack is also not open when debugging. And it is getting faster and faster to get the deadline of the procedure. Today, the program is changed to each thread to establish a connection, and the result is stable. It seems that it is also necessary to establish a connection for each thread through the ADO to invoke the database.
