Map-reduce / reduce: command mode and `tar_command_bootstrap`#

TypedJob vs command strings#

Production client (client_prod) treats each leg as either:

yt.TypedJob — pickled spec, typed table I/O helpers.
Command string — JsonFormat on stdin/stdout (e.g. ytjobs.mapper.BatchMapper).

Mapper and reducer must use the same kind (both TypedJob or both strings). Mixing them raises ValueError from run_map_reduce.

Note

Helpers such as ytjobs.mapper.BatchMapper are documented under YT jobs library (ytjobs).

Problem this solves#

For map, the framework always ships a bootstrap command: extract source.tar.gz, then run operation_wrapper_<stage>_map.sh.

Historically, map_reduce / reduce only listed the tarball as a file dependency without that bootstrap, so command-string legs could run with the archive present but not extracted.

Opt-in: `tar_command_bootstrap`#

In client.operations.map_reduce or client.operations.reduce, set:

tar_command_bootstrap: true

max_row_weight is optional in both sections and defaults to 128M when omitted.

Behavior:

Leg kind	Effect
Both TypedJob (map-reduce)	Unchanged: no bash bootstrap; YT handles TypedJob.
Both strings (map-reduce)	Each leg becomes `bash -c 'tar -xzf source.tar.gz && ./operation_wrapper_<stage>_map_reduce_mapper.sh'` (mapper) and the analogous `_reducer.sh` for the reducer.
TypedJob (reduce-only)	Flag ignored for packaging (TypedJob path unchanged).
String (reduce-only)	Reducer becomes `bash -c '… && ./operation_wrapper_<stage>_reduce.sh'`.

Default is false so existing TypedJob pipelines need no config change.

Wrappers in the tarball#

build_code_locally(..., create_wrappers=True) (used before upload) generates:

operation_wrapper_<stage>_map_reduce_mapper.sh
operation_wrapper_<stage>_map_reduce_reducer.sh
operation_wrapper_<stage>_reduce.sh

They mirror map wrappers: PYTHONPATH, JOB_CONFIG_PATH, optional pip install -r requirements.txt, then python3 stages/<stage>/src/<script>.py.

Which Python files run#

Optional entries in stages/<stage>/config.yaml:

job:
  map_reduce_command:
    mapper_script: mapper.py        # default
    reducer_script: reducer_mds.py  # if not `reducer.py`
  reduce_command:
    reducer_script: reducer_index.py

If omitted, the uploader picks defaults (e.g. first existing among reducer.py, reducer_mds.py, … for map-reduce reducer; a similar order for reduce-only).

Removability#

Logic lives mainly in yt_framework/operations/tar_command_wiring.py, job_command.py, and branches in dependency_strategy.py / map_reduce.py.
Disable by omitting tar_command_bootstrap or setting it false.

Dev client#

client_dev does not execute map-reduce legs; it logs whether each leg would be TypedJob or command (JsonFormat in prod) for sanity checks.

Map-reduce / reduce: command mode and tar_command_bootstrap#