EPICS Collaboration Meeting

1
Jefferson LabChannel Access Nameserver

• Talk by Karen White
• WORK by Joan Sage

2
Background

• By default, EPICS does not use a nameserver
• All process variable name resolution achieved via
  UDP broadcasts to all IOCs

3
Why Did We Want a Nameserver?

• Reduce IOC CPU load and network traffic due to
  broadcast requests for name resolution
• Provide PV location information for tools that do
  not require connection
• Improve client connection time
• Protect IOCs from loading caused by poorly
  written clients
• Simplify some Control System management and
  access functions

4
Why Replace our cdev Nameserver?

• Old JLab Nameserver
• Integration with client programs required code
  changes and recompilation
• Required changes to Channel Access Library
• Did not learn about new PVs
• Because of these difficulties, only BURT and MEDM
  (the most frequent UDP broadcasters) were ever
  modified to use the old Nameserver

5
New CA 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
• Created a simple script to turn Nameserver usage
  on and off for all programs initiated from a
  single operator console

6
New Nameserver - Startup

• 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
• Runs as a daemon with automatic restart in case
  of failure
• Startup time lt 5 sec (287,000 PVs)

7
New Nameserver IOC Reboots

• Nameserver monitors IOC heartbeat for connection
  events
• When an IOC goes down
• Nameserver 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

8
Without Nameserver
9
With Nameserver
10
New Nameserver Results

• Tested name resolution and connection - time to
  startup, resolving all names for an medm panel
  with gt 3000 PVs
• Without Nameserver 4.39 seconds
• With New Nameserver 2.18 seconds
• Nameserver has been used operationally for 1.5
  years without any problems
• Routinely handles over 6 million requests per day

11
Nameserver Gateways