incubator-airflow/airflow/models/pool.py

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from typing import Dict, Iterable, Optional, Tuple

from sqlalchemy import Column, Integer, String, Text, func
from sqlalchemy.orm.session import Session

from airflow.exceptions import AirflowException
from airflow.models.base import Base
from airflow.ti_deps.dependencies_states import EXECUTION_STATES
from airflow.typing_compat import TypedDict
from airflow.utils.session import provide_session
from airflow.utils.sqlalchemy import nowait, with_row_locks
from airflow.utils.state import State


class PoolStats(TypedDict):
    """Dictionary containing Pool Stats"""

    total: int
    running: int
    queued: int
    open: int


class Pool(Base):
    """the class to get Pool info."""

    __tablename__ = "slot_pool"

    id = Column(Integer, primary_key=True)
    pool = Column(String(256), unique=True)
    # -1 for infinite
    slots = Column(Integer, default=0)
    description = Column(Text)

    DEFAULT_POOL_NAME = 'default_pool'

    def __repr__(self):
        return str(self.pool)  # pylint: disable=E0012

    @staticmethod
    @provide_session
    def get_pool(pool_name, session: Session = None):
        """
        Get the Pool with specific pool name from the Pools.

        :param pool_name: The pool name of the Pool to get.
        :param session: SQLAlchemy ORM Session
        :return: the pool object
        """
        return session.query(Pool).filter(Pool.pool == pool_name).first()

    @staticmethod
    @provide_session
    def get_default_pool(session: Session = None):
        """
        Get the Pool of the default_pool from the Pools.

        :param session: SQLAlchemy ORM Session
        :return: the pool object
        """
        return Pool.get_pool(Pool.DEFAULT_POOL_NAME, session=session)

    @staticmethod
    @provide_session
    def slots_stats(
        *,
        lock_rows: bool = False,
        session: Session = None,
    ) -> Dict[str, PoolStats]:
        """
        Get Pool stats (Number of Running, Queued, Open & Total tasks)

        If ``lock_rows`` is True, and the database engine in use supports the ``NOWAIT`` syntax, then a
        non-blocking lock will be attempted -- if the lock is not available then SQLAlchemy will throw an
        OperationalError.

        :param lock_rows: Should we attempt to obtain a row-level lock on all the Pool rows returns
        :param session: SQLAlchemy ORM Session
        """
        from airflow.models.taskinstance import TaskInstance  # Avoid circular import

        pools: Dict[str, PoolStats] = {}

        query = session.query(Pool.pool, Pool.slots)

        if lock_rows:
            query = with_row_locks(query, **nowait(session))

        pool_rows: Iterable[Tuple[str, int]] = query.all()
        for (pool_name, total_slots) in pool_rows:
            pools[pool_name] = PoolStats(total=total_slots, running=0, queued=0, open=0)

        state_count_by_pool = (
            session.query(TaskInstance.pool, TaskInstance.state, func.count())
            .filter(TaskInstance.state.in_(list(EXECUTION_STATES)))
            .group_by(TaskInstance.pool, TaskInstance.state)
        ).all()

        # calculate queued and running metrics
        count: int
        for (pool_name, state, count) in state_count_by_pool:
            stats_dict: Optional[PoolStats] = pools.get(pool_name)
            if not stats_dict:
                continue
            # TypedDict key must be a string literal, so we use if-statements to set value
            if state == "running":
                stats_dict["running"] = count
            elif state == "queued":
                stats_dict["queued"] = count
            else:
                raise AirflowException(f"Unexpected state. Expected values: {EXECUTION_STATES}.")

        # calculate open metric
        for pool_name, stats_dict in pools.items():
            if stats_dict["total"] == -1:
                # -1 means infinite
                stats_dict["open"] = -1
            else:
                stats_dict["open"] = stats_dict["total"] - stats_dict["running"] - stats_dict["queued"]

        return pools

    def to_json(self):
        """
        Get the Pool in a json structure

        :return: the pool object in json format
        """
        return {
            'id': self.id,
            'pool': self.pool,
            'slots': self.slots,
            'description': self.description,
        }

    @provide_session
    def occupied_slots(self, session: Session):
        """
        Get the number of slots used by running/queued tasks at the moment.

        :param session: SQLAlchemy ORM Session
        :return: the used number of slots
        """
        from airflow.models.taskinstance import TaskInstance  # Avoid circular import

        return (
            session.query(func.sum(TaskInstance.pool_slots))
            .filter(TaskInstance.pool == self.pool)
            .filter(TaskInstance.state.in_(list(EXECUTION_STATES)))
            .scalar()
        ) or 0

    @provide_session
    def running_slots(self, session: Session):
        """
        Get the number of slots used by running tasks at the moment.

        :param session: SQLAlchemy ORM Session
        :return: the used number of slots
        """
        from airflow.models.taskinstance import TaskInstance  # Avoid circular import

        return (
            session.query(func.sum(TaskInstance.pool_slots))
            .filter(TaskInstance.pool == self.pool)
            .filter(TaskInstance.state == State.RUNNING)
            .scalar()
        ) or 0

    @provide_session
    def queued_slots(self, session: Session):
        """
        Get the number of slots used by queued tasks at the moment.

        :param session: SQLAlchemy ORM Session
        :return: the used number of slots
        """
        from airflow.models.taskinstance import TaskInstance  # Avoid circular import

        return (
            session.query(func.sum(TaskInstance.pool_slots))
            .filter(TaskInstance.pool == self.pool)
            .filter(TaskInstance.state == State.QUEUED)
            .scalar()
        ) or 0

    @provide_session
    def open_slots(self, session: Session) -> float:
        """
        Get the number of slots open at the moment.

        :param session: SQLAlchemy ORM Session
        :return: the number of slots
        """
        if self.slots == -1:
            return float('inf')
        else:
            return self.slots - self.occupied_slots(session)