how to configure Psersistence as a FIFO style?

[rosen jiang]

hi all,
i encounter a problem, i want limit the size of Store Usage, so i use:

                SystemUsage sy = broker.getSystemUsage();
                StoreUsage su = new StoreUsage();
                su.setLimit(3054432);
                sy.setStoreUsage(su);

YES, in my case, those codes could limit Store Usage, but those codes suspend my Producer sent message.
so, i want know, how to configure Psersistence as a FIFO style(Producer kept sending  new messages corresponding to first one message deleted)?

best,
rosen jiang