shared memory cannot allocate large pool

I looked at the alert log and saw the message:

ORA-04031: unable to allocate 2048024 bytes of shared memory ("large pool","unknown object","large pool","PX msg pool")

I looked at the trace file, and seems like one of the sql statement might be the culprit. When last time we had the issue with shared memory unable to allocate shared pool, I was not even able to login to the database. This time, no one really complained about anything. But then, my experience is mostly with manually configured SGA, this is version 11.2.0.2 with SGA_TARGET and SGA_MAX_SIZE auto managed memory. Does it mean, when the issue happened, the auto memeory management, automatically assigned a larger size and people are still able to login? Please advise. Thank you very