LISTSERV 16.5 - XROOTD-L Archives

ciao Andy!

On Mon, Aug 24, 2020 at 9:19 PM Andrew Hanushevsky <[log in to unmask]> wrote:

Hi Tommaso,

Are we talking about parallel sources or fallback sources?

to be exact, none of the two. For me, given two sources A and B:

- fallback: try A and if that does not work try B

- parallel: read from A and B at the same time

what I need instead is

- try A or B (with 50% probability) -- so a round robin between sources

TFile::Open
never could handle multiple *parallel* sources. Remember that you always
get multiple fallback sources as long as there is a redirector or the
multiple sources are registered in DNS. You just don't use them in
parallel except for xrdcp because that's where it's most effective.

That said, you can give TFile::Open a metalink file (one that ends in
"meta4") that lists all the possible sources.

that is indeed interesting!

I am searching on the web, if you happen to have more resources please let me know...

You just need to construct
one, it's not incredibly difficult and there may be some tools out there
that will do it for you (though I haven't been able to find any that
aren't tied to some larger project). So, if you are looking for "fallback"
sources metalink files are the fastest way to accomplish it today.

Andy

Thanks !

tom

On Mon, 24 Aug 2020, Tommaso boccali wrote:

> ciao Andy, thanks for your answer.
> I understand it will be solved for the xrdcp case. But what about a
> standard TFile::Open? Do I understand correctly that since it accepts an
> URL, it will not be possible to specify multiple sources in round robin?
>
> thanks again
>
> tom
>
> On Mon, Aug 24, 2020 at 6:50 AM Andrew Hanushevsky <
> [log in to unmask]> wrote:
>
>> Hi Tommaso,
>>
>> Ah, you are used to the "old" way of itentifying multiple endpoint using a
>> comma separated list in he URL. That is no longer supported as it was,
>> rightfully, pointed out that it is a violation of the URL standard. I
>> agree with you tat it would be nice to do it this way but the gaurds of
>> the standard won't allow it. The --sources option is used to add
>> additional sources and additional endpoints come from a redirector or
>> from DNS (or both). That is the only official way of doing it.
>>
>> That said, be out on the lookout on for xrdcp extensions that allow you to
>> list additional sources via an option. We are in the process of allowing
>> that.
>>
>> Andy
>>
>>
>> On Fri, 21 Aug 2020, Tommaso boccali wrote:
>>
>>> Ciao, in the xrootd code I find (e.g.
>>> https://root.cern.ch/root/html516/src/TXNetFile.cxx.html)
>>>
>>>
>>> // a. open a non-ROOT
>>> <https://root.cern.ch/root/html516/ROOT.html> generic file
>>> //
>> "root://server1:port1[,server2:port2,...]/pathfile?filetype=raw"
>>>
>>>
>>>
>>> as a way to instruct the client to probe more than 1 server.
>>>
>>> but if I try it, it does not seem to work:
>>>
>>> [a07cms04@r113c02s03 CMSSW_11_1_2]$ xrdcp -f 'root://
>>> r171c01s01.marconi.cineca.it,
>>>
>> r171c01s02.marconi.cineca.it///store/test/xrootd/T1_IT_CNAF/store/mc/SAM/GenericTTbar/AODSIM/CMSSW_9_2_6_91X_mcRun1_realistic_v2-v1/00000/A64CCCF2-5C76-E711-B359-0CC47A78A3F8.root
>> '
>>> .
>>> [0B/0B][100%][==================================================][0B/s]
>>> Run: [FATAL] Invalid address
>>>
>>> isn't is supported any more?
>>>
>>> And, assuming it still works, I understand it is not a round robin
>> between
>>> servers, but a failover to the second if the first is not ok.
>>>
>>> Is there a way instead to use a random one between those provided, such
>>> that to implement a "client side" round robin?
>>>
>>> thanks
>>>
>>> tom
>>>
>>>
>>>
>>> --
>>> Tommaso Boccali
>>> INFN Pisa
>>>
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>>
>
> --
> Tommaso Boccali
> INFN Pisa
>
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Tommaso Boccali
INFN Pisa