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---++ Mass file handling on the Grid (the GSTREAM library)

_Note_: The GSTREAM library is installed on the [[http://www.grid.kfki.hu/twiki/bin/view/KFKIAFS/AfsSoftwares#GSTREAM_The_GSTREAM_library][KFKI AFS]]. Look at that page for instructions on activation.

---+++ The GSTREAM library for read/write C++ streams to Storage Elements

As one does generally not want to always stage out the data files from SE-s onto a local disk by hand, and then process it, it is recommended to have read/write streams. The C++ library [[%ATTACHURL%/gstream.tar.gz][GSTREAM]] implements such a library. ( =gstream=, =igstream=, =ogstream= stream classes, like the usual C++ STL =fstream=, =ifstream=, =ofstream= file input/output stream classes; the letter 'g' standing for 'grid'.) It does nothing else, but treats the file as a normal file, unless its name begins with the string =/grid/=. In this case, it stages out the datafile in question onto a local (or AFS) area, and then treats the local file as a normal file. Sooner or later this solution has to be replaced with a GFAL based C++ library.

One commonly faces the problem that the file not only has to be processed, but it also has to be passed through a filter program. Therefore I also wrote pipe streams for grid storage ( =igpstream=, =ogpstream=), which are based on the =ipstream= and =opstream= classes of the library at [[http://pstreams.sourceforge.net][http://pstreams.sourceforge.net]] (note the LGPL license!).

Practical examples:

<verbatim>
#include "gstream.h"

int main(int argc, char *argv[])
{
    // Open the datafile for reading.
    igstream igfile("/grid/cms/alaszlo/some_datafile.dat");
        // Extract data from your datafile with 'igstream::operator>>' or with 'igstream::read(char*, int)'.
    // Close the datafile.
    igfile.close();
    igfile.clear();

    // Open the datafile for writing.
    ogstream ogfile("/grid/cms/alaszlo/some_datafile.dat");
        // Write data to your datafile with 'ogstream::operator<<' or with 'ogstream::write(char*, int)'.
    // Close the datafile.
    ogfile.close();
    ogfile.clear();

    // Open the datafile for reading, through a filter program.
    igpstream igpfile("/grid/cms/alaszlo/some_datafile.dat.gz", "gunzip --stdout %f");
        // Extract data from your datafile with 'igpstream::operator>>' or with 'igpstream::read(char*, int)'.
    // Close the datafile.
    igpfile.close();
    igpfile.clear();

    // Open the datafile for writing, through a filter program.
    ogpstream ogpfile("/grid/cms/alaszlo/some_datafile.dat.gz", "gzip - > %f");
        // Write data to your datafile with 'ogpstream::operator<<' or with 'ogpstream::write(char*, int)'.
    // Close the datafile.
    ogpfile.close();
    ogpfile.clear();

    return 0;
}
</verbatim>

When compileing, pass the option =`gstream-config --cflags`= to the compiler, and when linking, pass the =`gstream-config --libs`= option to the linker.

Before usage, one has to export the following environmental variables:

<verbatim>export LCG_GFAL_VO=your_vo</verbatim> (for _bash_), or <verbatim>setenv LCG_GFAL_VO your_vo</verbatim> (for _tcsh_), and

<verbatim>export DEST=your_favourite_storage_element1,your_storage_element2,...</verbatim> (for _bash_), or <verbatim>setenv DEST your_favourite_storage_element1,your_storage_element2,...</verbatim> (for _tcsh_).

Setting the environmental variable =TMPDIR= is optional. This specifies the local (or AFS) directory, where the datafiles are staged out (therefore, it has to have large disk space!). E.g.:

<verbatim>export TMPDIR=/tmp</verbatim> (for _bash_), or <verbatim>setenv TMPDIR /tmp</verbatim> (for _tcsh_).

If not specified, the current working directory ( =$PWD=) is used, as this is recommended for grid jobs (the working nodes have large disk spaces).

---+++ GSTREAM toolkit extensions for command line mass file manipulations

Some helper scripts are also shipped together with the GSTREAM library. The wrapper scripts =lcg-cr.sh=, =lcg-rep.sh=, =lcg-cp.sh=, =lcg-del.sh= provide wrappers around the commands =lcg-cr=, =lcg-rep=, =lcg-cp=, =lcg-del=, such that whole directory trees can also be handled. Wrappers around other =lcg-= commands may be also written based on them (in this case, we would be grateful to be shared with them). These scripts provide text outputs of the planned series of =lfc-= and =lcg-= commands. This text output can be passed to the script =runplan.sh=, which executes the command list. Every command is included in a checker loop: execution is given up after 5 unsuccessful tries. If any interruption occures (e.g. because of failure), the =runplan.sh= script can be started again, and will continue from the command, where it got interrupted.

Practical examples:

<verbatim>
> lcg-cr.sh  /home/user_name/source  /grid/your_vo/user_name/destination  your_favourite_se  your_vo  > runplan.dat
> runplan.sh  runplan.dat
</verbatim> Here =source= may be large directory tree structure.

<verbatim>
> lcg-rep.sh  /grid/your_vo/user_name/source  destination_se  your_vo  > runplan.dat
> runplan.sh  runplan.dat
</verbatim> Here =source= may be large directory tree structure. =destination_se= is the SE, where you want the replica.

<verbatim>
> lcg-cp.sh  /grid/your_vo/user_name/source  /home/user_name/dest  your_vo  > runplan.dat
> runplan.sh  runplan.dat
</verbatim> Here =source= may be large directory tree structure.

<verbatim>
> lcg-del.sh  /grid/your_vo/user_name/target  target_se  your_vo  > runplan.dat
> runplan.sh runplan.dat
</verbatim>

Here =target= may be large directory tree structure, and =target_se= is the SE, from where you want to remove your copy. Setting it to =all= means removal of all replicas. 

The wrapper scripts may be improved in the future. We thank to Kálmán K&#337;vári for this toolkit. There are also other useful scripts in the package. Please have a look a them.

Also the scripts =gexists.sh=, =gput.sh=, =grep.sh=, =gget.sh=, =gdel.sh= may be helpful to manipulate single files.


-- Main.AndrasLaszlo - 10 Jul 2009
Attachments
Topic attachments
I	Attachment	History	Action	Size	Date	Who	Comment
gz	gstream.tar.gz	r5 r4 r3 r2 r1	manage	18.7 K	2008-11-23 - 17:38	AndrasLaszlo	The GSTREAM library source.
Topic revision: r10 - 2009-07-10 - AndrasLaszlo
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