It is well known, that connection storms can cause severe trouble and rwloadsim has been created to avoid them if at all possible. If you are using session pools, only specifying the maximum pool size will make OCI create all the connections when the pool is created, i.e. when the database is declared. If you specify both the minimum and maximum pool size, the minimum will be created when the database is declared, but the pool may suddenly increase to its maximum size if needed by your workload. If you are using dedicated connections, rwloadsim will create one for each thread, and this will be done serially before the threads actually start running.
The -c option (control loop start time) is important with respect to this. Rwloadsim is created such that all control loops (typically one per thread) actually start working at (approximately) the same time, which will be some seconds after start of rwloadsim. This time is what the -c option specifies. The default is (arbitrarily) chosen at 5s, which should allow moderately sized session pools and moderate counts of threads with dedicated connections to complete connection ramp up before actually starting. If you have large session pools or large number of threads with dedicated connections, you are strongly advised to increase the control loop start time. You can similarly decrease it if you have very low counts. If the start time is not sufficient, you will both risk connection storms, and there is a risk that control loops will start too late. See the description of the start, wait and every options to control loops.
Particular care is needed if you are using multi process execution.
Note that all start times are approximate, and that they can vary as the Operating System isn’t a real-time Operating System. The actual implementation of the start times is via the clock_nanosleep() system call with a first argument of CLOCK_REALTIME and a second argument of TIMER_ABSTIME; see the notes of the clock_nanosleep(2) manual page.
The control loop start time is saved in the results database as an ORACLE date in the rdate column of the rwlrun table; this is always in UTC timezone irrespective of your settings.