Transaction are not flowing to DB

Hi,

   Here is the scenario i came across at one of our store.At morning they started running the sales and one hour suddenly the transaction didn't hit the db.I just restarted the store server and transaction start following in to the db.But there are about 100 transaction were missing at  that period  and they were all flown to Queue exception. Now my question why this happens frequently.

POS version is :12.0.9

IBM websphere application server.

Thanks,

santhosh.