LISTSERV mailing list manager LISTSERV 16.5

Help for XROOTD-L Archives


XROOTD-L Archives

XROOTD-L Archives


XROOTD-L@LISTSERV.SLAC.STANFORD.EDU


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Proportional Font

LISTSERV Archives

LISTSERV Archives

XROOTD-L Home

XROOTD-L Home

XROOTD-L  August 2006

XROOTD-L August 2006

Subject:

Re: Quering locations of a vector of files

From:

Fabrizio Furano <[log in to unmask]>

Date:

18 Aug 2006 20:46:01 +0200Fri, 18 Aug 2006 20:46:01 +0200

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (178 lines)

Hi Jan,

  I see, imho this means that there is very little overhead you can 
overlap, at least on the client side. Or that you are opening all those 
files towards very few servers, or the same one. I hope not.

  Anyway the async open was not meant as a way to speed up the open 
primitive, but as a way to do other things while the open is in 
progress, or to stage many files in parallel without serializing the 
waits. But in your situation it seems that there are not so many waits 
to parallelize.

Fabrizio


Jan Iwaszkiewicz wrote:
> Hi!
> 
> I have done some test as Fabrizio advised.
> The results of tests with asynchronous open are similar to those with 
> standard open:
> 
> I used the following code:
> 
>   TTime starttime = gSystem->Now();
>    TList *toOpenList = new TList();
>    toOpenList->SetOwner(kFALSE);
>    TIter nextElem(fDset->GetListOfElements());
>    while (TDSetElement *elem = dynamic_cast<TDSetElement*>(nextElem())) {
>       TFile::AsyncOpen(elem->GetFileName());
>       toOpenList->Add(elem);
>    }
> 
>    TFile::EAsyncOpenStatus aos;
>    TIter nextToOpen(toOpenList);
>    while (toOpenList->GetSize() > 0) {
>       while (TDSetElement* elem = 
> dynamic_cast<TDSetElement*>(nextToOpen())) {
>          aos = TFile::GetAsyncOpenStatus(elem->GetFileName());
>          if (aos == TFile::kAOSSuccess || aos == TFile::kAOSNotAsync
>              || aos == TFile::kAOSFailure) {
>             elem->Lookup();
>             toOpenList->Remove(elem);
>          }
>          else if (aos != TFile::kAOSInProgress)
>             Error("fileOpenTestTmp", "unknown aos");
>       }
>       nextToOpen.Reset();
>    };
>    toOpenList->Delete();
> 
>    TTime endtime = gSystem->Now();
>    Float_t time_holder = Long_t(endtime-starttime)/Float_t(1000);
>    cout << "Openning time was " << time_holder << " seconds" << endl;
> 
> 
> The result is:
> 
> #files    asynchronous        standard TFile::Open
> 300    12.5            11.7
> 240    9.68            9.4
> 120    4.5            4.6
> 
> Have a nice weekend!
> Jan
> 
> Jan Iwaszkiewicz wrote:
>> Hi Fabrizio, Hi Andy!
>>
>> Thank you for the answers.
>> I'm making tests with TFile::AsyncOpen and will keep you informed. 
>> Maybe I should clarify that we want to lookup locations of the files 
>> on the PROOF master node but then open the files on worker nodes. The 
>> point of the lookup is to determine what files each worker will 
>> open/process. For the problems that Andy described:
>> 1) I agree. 2) It seems to be even more important to parallelize it.
>>
>> In fact the possibility to get all locations of a file is also high on 
>> our wish-list. It would prevent us from opening a remote file while 
>> another copy is on one of our workers. We have no mechanism to avoid 
>> it. I think it's quite different use case than file serving. We want 
>> to make best use of a set of nodes belonging to a PROOF session. It 
>> would be very usefull to have this functionality!
>> Cheers,
>> Jan
>>
>> -----Original Message-----
>> From: Andrew Hanushevsky [mailto:[log in to unmask]]
>> Sent: Wed 8/16/2006 10:47 PM
>> To: Fabrizio Furano; Jan Iwaszkiewicz
>> Cc: [log in to unmask]; [log in to unmask]; Gerardo Ganis
>> Subject: Re: Quering locations of a vector of files
>>  
>> Hi Jan,
>>
>> Another way to speed up the processing is to use the Prepare method 
>> that allows you to set in motion all the steps needed to get file 
>> location information. As far as finding out the location of a list of 
>> files, that may be doable but has problems of its own. In your case it 
>> probably doesn't matter but in the general case two things may happen: 
>> 1) the location may be incorrect by the time you get the information 
>> (i.e., the file has been moved or deleted), and 2) there is no 
>> particular location for files that don't exist yet (this includes 
>> files that may be in an MSS but not yet on disk). The latter is more 
>> problematical as it takes a while to determine that. Anyway, we'll 
>> look into a mechanism to get you file location information (one of n 
>> for each file) using a list.
>>
>> Andy
>>
>> ----- Original Message ----- From: "Fabrizio Furano" 
>> <[log in to unmask]>
>> To: "Jan Iwaszkiewicz" <[log in to unmask]>
>> Cc: <[log in to unmask]>; "Maarten Ballintijn" 
>> <[log in to unmask]>; "Gerri Ganis" <[log in to unmask]>
>> Sent: Wednesday, August 16, 2006 10:09 AM
>> Subject: Re: Quering locations of a vector of files
>>
>>
>>> Hi Jan,
>>>
>>>  at the moment such a primitive is not part of the protocol. The 
>>> simpler way of doing it is to call Stat for each file, but this 
>>> reduces the per-file overhead only by a small amount, with respect to 
>>> a Open call.
>>>  In fact, both primitives actually drive the client to the final 
>>> endpoint (the file), so you cannot avoid the overhead (mainly 
>>> communication latencies) of being redirected to other servers.
>>>
>>>  Since you say it's critical for you, my suggestion is to open as 
>>> many files as you can in the parallel way. Doing so, all the 
>>> latencies are parallelized, and you can expect a much higher 
>>> performance.
>>>
>>>  To do this, just call TFile::AsyncOpen(fname) for each file you need 
>>> to open (a cycle), and then, later, you can call the regular 
>>> TFile::Open (another cycle).
>>>   The async call is non-blocking and very fast. You can find an 
>>> example of its ROOT-based usage here:
>>>
>>> http://root.cern.ch/root/Version512.news.html
>>>
>>>  The ugly thing is that doing this you are using a lot of resources, 
>>> so, if you have really a lot of files to open (let's say, 5000) and 
>>> the resources are a problem, maybe you can find a workaround by 
>>> opening them in bunches of fixed size.
>>>
>>> Fabrizio
>>>
>>> Jan Iwaszkiewicz wrote:
>>>> Hi,
>>>>
>>>> In PROOF we realized that we need a possibility to query exact 
>>>> locations of a set of files. As far as I have seen in the xrootd 
>>>> protocol, there is no way to ask for locations of a vector of files.
>>>>
>>>> At the beginning of a query, we want to check exact locations of all 
>>>> the files form a data set. The current implementation does it by 
>>>> opening all the files, one by one.
>>>> The speed is about 30 files/sec. For many queries, the lookup takes 
>>>> much longer than the processing.
>>>> It is a critical problem for us.
>>>>
>>>> The bool XrdClientAdmin::SysStatX(const char *paths_list, kXR_char 
>>>> *binInfo) method can check multiple files but it only verifies 
>>>> whether the files exist.
>>>> I imagine that it would be best for us to have something similar but 
>>>> returning file locations. Is such an extension to the protocol 
>>>> possible/reasonable to implement?
>>>>
>>>> Cheers,
>>>> Jan
>>
>>
>>


Top of Message | Previous Page | Permalink

Advanced Options


Options

Log In

Log In

Get Password

Get Password


Search Archives

Search Archives


Subscribe or Unsubscribe

Subscribe or Unsubscribe


Archives

March 2024
February 2024
January 2024
December 2023
November 2023
October 2023
September 2023
August 2023
July 2023
June 2023
May 2023
April 2023
March 2023
February 2023
January 2023
December 2022
October 2022
September 2022
August 2022
July 2022
June 2022
May 2022
April 2022
March 2022
February 2022
January 2022
December 2021
November 2021
October 2021
September 2021
August 2021
July 2021
June 2021
May 2021
April 2021
March 2021
February 2021
January 2021
December 2020
November 2020
October 2020
September 2020
August 2020
July 2020
June 2020
May 2020
April 2020
March 2020
February 2020
January 2020
December 2019
November 2019
October 2019
September 2019
August 2019
July 2019
June 2019
May 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
July 2018
June 2018
May 2018
April 2018
March 2018
February 2018
January 2018
December 2017
November 2017
October 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
November 2016
October 2016
September 2016
August 2016
July 2016
May 2016
April 2016
March 2016
February 2016
January 2016
December 2015
November 2015
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
September 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
October 2012
September 2012
August 2012
July 2012
June 2012
May 2012
April 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
October 2010
September 2010
August 2010
July 2010
June 2010
May 2010
April 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
July 2009
June 2009
May 2009
April 2009
March 2009
January 2009
December 2008
September 2008
August 2008
July 2008
June 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
October 2007
September 2007
August 2007
July 2007
June 2007
May 2007
April 2007
March 2007
February 2007
January 2007
December 2006
November 2006
October 2006
September 2006
August 2006
July 2006
June 2006
May 2006
April 2006
March 2006
February 2006
January 2006
December 2005
November 2005
October 2005
September 2005
August 2005
July 2005
June 2005
May 2005
April 2005
March 2005
February 2005
January 2005
December 2004
November 2004
October 2004
September 2004
August 2004

ATOM RSS1 RSS2



LISTSERV.SLAC.STANFORD.EDU

Secured by F-Secure Anti-Virus CataList Email List Search Powered by the LISTSERV Email List Manager

Privacy Notice, Security Notice and Terms of Use