10.5. Staging Mappers

Starting 4.7 release, Pegasus has support for staging mappers in the nonsharedfs data configuration. The staging mappers determine what sub directory on the staging site a job will be associated with. Before, the introduction of staging mappers, all files associated with the jobs scheduled for a particular site landed in the same directory on the staging site. As a result, for large workflows this could degrade filesystem performance on the staging servers.

To configure the staging mapper, you need to specify the following property

pegasus.dir.staging.mapper  <name of the mapper to use>

The following mappers are supported currently, with Hashed being the default .

  1. Flat : This mapper results in Pegasus placing all the job submit files in the staging site directory as determined from the Site Catalog and planner options. This can result in too many files in one directory for large workflows, and was the only option before Pegasus 4.7.0 release.

  2. Hashed : This mapper results in the creation of a deep directory structure rooted at the staging site directory created by the create dir jobs. The binning is at the job level, and not at the file level i.e each job will push out it's outputs to the same directory on the staging site, independent of the number of output files. To control behavior of this mapper, users can specify the following properties

    pegasus.dir.staging.mapper.hashed.levels     the number of directory levels used to accomodate the files. Defaults to 2.
    pegasus.dir.staging.mapper.hashed.multiplier the number of files associated with a job in the submit directory. defaults to 5.


The staging mappers are only triggered if pegasus.data.configuration is set to nonsharedfs