Transfer Agents

Transfer agents run as standalone (C++) daemons, and use Oracle as the database backend.

DAO

The DAO layer is responsible for database interaction.

DAO objects are used by Action objects.

Actions

Classes deriving from Action use the DECLARE_FACTORY_METHOD and REGISTER_FACTORY_METHOD macros to create a subclass of the ActionFactoryMethod class and to register an instance of the subclass to the ActionFactory singleton instance.

The SchedulerEntry class calls execute on the Action objects, passing its internal action parameters string.

Channel agents and VO agents read the configuration parameters and add SchedulerEntry objects to an ActionScheduler.

Actions get user's credentials through MyProxy or from the DB according to the configuration (see getProxyForJob function). For each job are stored into the database:

• the user DN
• one among:
  • user's MyProxy passphrase (USER_CRED field)
  • delegated credentials ID (CRED_ID field). With this option VOMS roles are supported.

Channel Actions

Channel agents use a cache for active transfers; when a DAOException is trapped, the active transfers cache must be cleaned (since an error interacting with the database occurred, it is not possible to grant the integrity of the cache).

New transfers are added to the cache by the Fetch action, and removed by Cancel or CheckState.

Cancel (channel action)

CheckState (channel action)

Fetch (channel action)

CleanSDCache (channel action)

HeartBeat (channel action)

Active Transfers Cache

VO Actions

The VOAgent has a cache for channel allocation – used above all because of fallback logic for groups/clouds. The channels cache is used only by the Allocate action. The search is performed in two steps: first, a match is searched for the two SEs (A -> B), then if it's not found, the agent determines if this is due to the fact that the match was not in the cache or because it doesn't exist (process is split in 2 steps to keep the cache simple).

Retry (vo action)

The classes BasicRetry and PythonRetry extend the base Retry class.

Allocate (vo action)

The VO agent options “enable unknown source/destination” are used to determine if SEs not handled by service discovery are supported. In such a case, the SE is assigned to the “UNKNOWN” site (reserved keyword; sites must not be called UNKNOWN) so that it will be matched by a catch all channel '*'.

CheckReadiness (vo action)

Currently does nothing (pre-staging is not yet supported). A pre-staging policy will be needed (share per channel), it is not possible to pre-stage everything.

Finalize (vo action)

Has 2 purposes:

• perform the done->finishing transition
• call a hook

CleanSDCache (vo action)

HeartBeat (vo action)

Maintainer: PaoloTedesco