NOTICE:  RegisterSharedInvalid: SI buffer overflow
NOTICE:  InvalidateSharedInvalid: cache state reset
NOTICE:  RegisterSharedInvalid: SI buffer overflow
NOTICE:  InvalidateSharedInvalid: cache state reset
NOTICE:  RegisterSharedInvalid: SI buffer overflow
NOTICE:  InvalidateSharedInvalid: cache state reset

A note on one of the mailing lists indicates that this can happen if someone has an open transaction. In my case bouncing tomcat did the trick.

The pass-through device for GPM is /dev/gpmdata.