List of Xrootd 4 Features (from Andy Hanushevsky)


1)  IPv6 aupport,
2)  Public-private networking support,
3)  Improved monitoring linkage between client application & server usage,
   Specifically, the allows one to easily capture a job.s identification
   (e.g. the Panda job ID).
4)  New disconnect record for the f-stream,
5)  Disk caching proxy server,
6)  Substantially improved proxy server offering better scalability and
   much lower overhead (e.g. vector read passthrough),
7)  Remote debugging facility,
8)  http/WebDav support,
9)  Ability to do manual log file rotation (e.g. via logrotate),
10) Selectable microsecond precision log file timestamps,
11) Ability to query the running state of the cmsd via xrootd query
   config,
12) Additional query options (role, sitename, checksum, etc),
13) Ability to dynamically blacklist sites from a federation,
14) New stat() function plug-in to accomodate additional file system that
   provide extended information (e.g. GPFS),
15) Allow the new client to be configurable via global and local
   configuration files,
16) Make third party copies cancellable,
17) Speed up directory listings,
18) Add additional client information to the monitoring identification
   record (e.g. application name), and
19) Fully utilize the new high performance client (i.e. xrdcp, proxy
   server, etc) to significantly improve scalability and performance.

Summary of issues (From Lukasz Janyst) 

1) Client compatibility

1a) Network - xrootd3 clients can talk to xroot4 servers and xrootd4 clients can talk to xrootd3 servers. No problem there.

1b) Libraries - API and ABI - no, there were slight changes in both, and xrootd4 client libs cannot be used with xrootd3 programs without recompiling and slight modification of the source.

1c) TNetXNGFile - the new ROOT plugin for xrootd - we have found (thanks to LHCb) some issues while accessing dCache sites:

1ca) while sending stat requests - fixed in the client and will be released with ROOT 5.34.21.

1cb) while processing readv requests - server-side configuration issues, essentially the dCache servers where advertising that they can handle the readv requests of sizes that they were unable to handle. To my knowledge, LHCb decided to contact the admins and ask them to fix the configuration.

1cc) LHCb also hit a rather annoying bug while handling readv requests client-side that was fixed in xrootd4 but not in xrootd3.

1d) ROOT vs XROOTD - some users, including ATLAS FAX would like to mix the clients, ie. use Athena with ROOT and xrootd3 but at the same time use xrootd4 xrdcp, which currently is problematic. I have discussed possible solutions to this issue with Pere Mato and others in the ROOT team and we will try to address this when Andy is at CERN next week.

2) EPEL - this really is outside of my "jurisdiction". I have contacted Mattias Ellert, who is responsible for EPEL packaging for xrootd, and kindly asked him to update. The current show stopper here is lack of ROOT release that would work well with xrootd4 - the problems are solved already and wait for root 5.34.21 to be released.

  From xrootd perspective - we have renamed out packages to xrootd4 to make the migration easier, especially for DPM sites, but whether EPEL will follow this convention remains unclear.

3) FTS - in order to be able to cancel 3rd party copy jobs FTS needs xrootd 4 both client and server-side. If the server side is xrootd3 third party copies should still work, but they won't be cancellable.