Controls Group New Channel Access Nameserver Joan Sage 12/4/01

Controls Group Overview Background Motivation Old JLab Nameserver New JLab Nameserver Results

Controls Group Background By default, EPICS does not use a nameserver Process variable name resolution achieved via UDP broadcasts JLab has used a cdev based nameserver for BURT and MEDM clients for several years

Controls Group EPICS PV Name Resolution IOC Client Broadcast TCP Connection

Controls Group Why Use A Nameserver? Reduce IOC CPU load due to broadcast requests for name resolution Provide PV location information for tools that do not require connection Improve client connection time

Controls Group Why A New JLab Nameserver? Old JLab Nameserver –Integration with client programs required code changes and recompilation –Required changes to Channel Access Library Because of these difficulties, the old nameserver was only used with BURT and MEDM

Controls Group New Nameserver No modifications needed to client code No modifications to Channel Access Library Client programs are configured to use nameserver by setting EPICS_CA_ADDR_LIST to the IP Address of the Nameserver host and by setting EPICS_CA_AUTO_ADDR_LIST to NO

Controls Group New Nameserver Nameserver reads signal.list files generated by IOCs at boot time to fill initial hash table Nameserver “learns” about PVs added to the system after startup by broadcasting to fill unknown PV requests

Controls Group New Nameserver Built on PCAS example code – directoryServer (Jeff Hill’s suggestion) pvExistTest reimplemented Heartbeat CA monitors for each IOC

Controls Group New Nameserver Runs as a daemon with automatic restart on failure (code stolen from CA Gateway) Nameserver Startup Time < 5 sec for 250K PVs

Controls Group New Nameserver Nameserver monitors IOC heartbeat for connection events When an IOC goes down –Hashtable updated –Nameserver monitors for reconnection events – Nameserver does not respond to clients asking for PVs on IOCS that are down Deleted and moved PVs are automatically handled

Controls Group New Nameserver NS Client IOC Broadcast TCP Connection Fallthrough* *Nameserver Hash Table IS Updated

Controls Group Results Tested name resolution and connection  10,465 PVs on 36 IOCs  Max 300 PVs/IOC Without Nameserver – 4.39 sec With New Nameserver – 2.18 sec Being used successfully for Jlab operations for 3 months

Controls Group Side Effects An extra computer is required to run the Nameserver Central “database” –Allows generation of a list of PVs that never resolve –Allows identification of duplicate PVs