FTI plugin

WARNING This documentation is a work in progress and does not reflect the full FTI plugin potential.

The FTI plugin enables one to perform checkpoints using FTI. FTI plugin does not support the full FTI feature set but offers a simple declarative interface to access a large subset of it.

Features and requirements

Dependencies

FTI plugin uses a MPI_Comm datatype and MPI_COMM_WORLD descriptor, which are defined in mpi plugin. For now it must be loaded alongside FTI plugin (as shown below).

pdi:
   ...

   plugins:
      mpi:
      fti:
         ...

Initialization

FTI initialization in FTI plugin is based on several rules:

• if init_on is specified, FTI plugin will initialize FTI on that exact event and expects the communicator and file name to be correctly available or fail otherwise,
• if init_on is not specified and the communicator is available on plugin initialization (e.g. when using MPI_COMM_WORLD predefine from mpi plugin), FTI plugin will try to initialize FTI (on plugin initialization) and expects file name to be correctly available or fail otherwise,
• if init_on is not specified and the communicator is not available on plugin initialization, FTI plugin will try to initialize FTI on communicators descriptor exposure and expects file name to be correctly available or fail otherwise.

Predefined descriptors

FTI plugin loads a predefined descriptor named FTI_COMM_WORLD (FTI_COMM_WORLD_F for Fortran) after a successfull initialization of FTI. This descriptor is treated as metadata. Its content can be accessed using PDI_access.

Configuration grammar

At its root, the FTI configuration is made of several nodes: checkpoint, communicator, config_file, dataset, init_on, recover_on, recover_var, send_file, snapshot_on and status.

checkpoint

A checkpoint specifies a list of checkpoints to execute. It is specified by a key/value map that may contain following keys: L1_on, L2_on, L3_on, L4_on. Each of the keys specifies events names that trigger a specified checkpoint. Value of this key can be either string or a list of strings:

• L1_on: executes FTI L1 checkpoint on specified PDI events,
• L2_on: executes FTI L2 checkpoint on specified PDI events,
• L3_on: executes FTI L3 checkpoint on specified PDI events,
• L4_on: executes FTI L4 checkpoint on specified PDI events.

communicator

A communicator is a string, which specifies name of descriptor containing a MPI communicator to use for FTI initialization. Additionally, FTI plugin can write FTI_COMM_WORLD into this descriptor, if it is shared with write access right. It defaults to MPI_COMM_WORLD, which is a predefined descriptor from mpi plugin.

config_file

A config_file is a string that can contain $-expressions. Specifies the name of the FTI configuration file.

dataset

A dataset is a key/value map, which keys are integers that specify datasets ids in FTI and values are names of protected descriptors. Alternatively, the map may contain a map with keys name and size, where name is a name of protected descriptor and size is a descriptor where FTI plugin will write size of the protected descriptor when shared with write access right.

dataset:
  0: {name: variable, size: variable_size}
  1: variable2

init_on

A init_on is a string or a list of strings that specifies the names of the PDI events that executes recovery of FTI.

recover_on

A recover_on is a string or a list of strings that specifies the names of the PDI events that executes recovery of FTI.

recover_var

A recover_var is a list of maps with keys:

• on_event
• var

on_event defines on which events the variable recovery should be done (single event or list of events)

var defines IDs of variables to recover (single ID or list of IDs)

plugins:
  fti:
    recover_var:
      - on_event: recover_test
        var: 2
      - on_event: [recover_arrays, dummy_event]
        var: [0, 1]

send_file

A send_file is a key/value map or a list of key/value maps describing source and destination paths of files to send, event or list of events to trigger on and optionally name of descriptor, where will be stored status information when exposed. Example:

send_file:
  on_even: event
  file:
    src: source_path
    dest: destination_path
    status: status_descriptor

snapshot_on

A snapshot_on is a string or a list of strings that specifies the names of the PDI events that executes FTI_Snapshot.

status

A status is a string that specifies the name of a descriptor to which FTI will write FTI_Status code when shared.

full configuration example

pdi:
  metadata: # type of small values for which PDI keeps a copy
    iter: int
    size:  { size: 2, type: int }
  data: # type of values for which PDI does not keep a copy
    fti_status: int
    array_size: int64
    file_name: {size: 64, type: array, subtype: char}
    file_status: int
    file1_status: int
    file2_status: int
    main_array: { size: ['$size[0]', '$size[1]'], type: array, subtype: double }

  plugins:
    mpi:
    fti:
      config_file: fti_config.ini
      communicator: MPI_COMM_WORLD
      init_on: fti_init_event
      status: fti_status
      dataset:
        0: {name: main_array, size: array_size}
        1: iter
      snapshot_on: snapshot_event
      recover_on: recover_event
      checkpoint:
        L1_on: ckpt_l1_event
        L2_on: [ckpt_l2_1_event, ckpt_l2_2_event]
        L3_on: [ckpt_l3_1_event, ckpt_l3_2_event]
        L4_on: ckpt_l4_event
      send_file:
        - on_event: send_one_file
          file:
            src: ./$file_name
            dest: ./somewhere_else/$file_name
            status: file_status
        - on_event: [send_two_files_first_event, send_two_files_second_event]
          file:
            - src: ./file1
              dest: ./somewhere_else/file1
              status: file1_status
            - src: ./file2
              dest: ./somewhere_else/file2
              status: file2_status