[GSM-WG] About synchronous srmLs with offset and count

[Riccardo Zappi]

Hi,
probably we have already discussed this, but I would like return to the 
topic because I'm not able to find, both in the current SRM 
specification and in the archives of various SRM mailing lists, a 
conclusive answer.

The doubt is in the interpretation of 'offset' and 'count' parameters in 
the case of a synchronous implementation of srmLs.

The problem arises when in addition to offset and count parameters, it 
is specified at least one directory within SURL array and 'numOfLevels' 
is greater than zero. In this case, some SURLs pointed out by the 
request are not enumerated in the requests (i.e. the files within the 
directory) and therefore, the list of files may be change between 
subsequent calls, since files can be added or removed from the directory 
by some other concurrent SRM requests.

For example, suppose you want list the content of a directory, and you 
do not know the exact number of files on it. Your first attempt fails 
with SRM_TOO_MANY_RESULTS, so you proceed with the use of count and 
offset. I think it is appropriate to suppose that SRM returns the lists 
of the files always in the same order, whatever it is.
Suppose that between two successive requests, one file is removed in the 
directory by another users/process, and that file fits in the part of 
list you already retrieved. In this case, your successive request skips 
one file, because your offset can take into account positions lose 
because of deletion from other SRM requests.

We believe it is appropriate to explain better in the SRM specification 
the behavior expected in the case of offset, count, 'numOfLevels'> 0 and 
directories, with a synchronous srmLs implementation.

Thanks in advance for any comments.

Cheers,
Riccardo

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Riccardo Zappi

Istituto Nazionale di Fisica Nucleare - CNAF
Viale Berti Pichat, 6/2,  40127 BOLOGNA - ITALY
Phone:  +39-051-609-2868                Fax:    +39-051-609-2746
e-mail: riccardo.zappi at cnaf.infn.it
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