GitHub user linwanlong edited a discussion: Tasks in a DAG cannot be executed
in parallel to find a solution
This is my environmental information
```text
Apache Airflow
version | 3.0.3
executor | LocalExecutor
```
Here's my config information
```text
[core]
default_timezone = utc
executor = LocalExecutor
parallelism = 32
max_active_tasks_per_dag = 16
max_active_runs_per_dag = 16
max_consecutive_failed_dag_runs_per_dag = 0
```
Here's my dag file
```python
from airflow.sdk import dag, task
import time
from airflow.providers.standard.operators.empty import EmptyOperator
@dag(schedule=None, catchup=False, tags=["verification"], max_active_tasks=10)
def busy_box():
@task
def task_a():
print("start task A")
time.sleep(10)
print("end task A")
@task
def task_b():
print("start task B")
time.sleep(10)
print("end task B")
@task
def task_c():
print("start task c")
time.sleep(10)
print("end task c")
start = EmptyOperator(task_id="start")
a = task_a()
b = task_b()
c = task_c()
end = EmptyOperator(task_id="end")
# a >> b # 串行
# 或者改成
start >> [a, b, c] >> end # 并行
busy_box_dag = busy_box()
```
Present the results
<img width="2235" height="603" alt="image"
src="https://github.com/user-attachments/assets/e41ad052-35c5-49ac-a16a-f1ad83b48376";
/>
Task C does not start until after the end of Task B. Sometimes the start time
of task A and task B is different (task B starts after task A ends), but this
problem is not encountered in Airflow2
This is about the process of airflow3
```text
root 2655981 0.0 0.2 128088 48592 pts/3 Sl+ 21:28 0:00
/root/miniconda3/envs/xxx/bin/python
/root/.vscode-server/extensions/ms-python.black-formatter-2025.2.0/bundled/tool/lsp_server.py
--stdio
root 2656190 0.1 0.9 190396 150140 pts/0 S+ 21:28 0:02 airflow
api_server -- host:0.0.0.0 port:8080
root 2656199 0.0 0.0 16752 10360 pts/0 S+ 21:28 0:00
/root/miniconda3/envs/xxxbin/python3.10 -c from
multiprocessing.resource_tracker import main;main(7)
root 2656200 0.3 1.4 487120 230024 pts/0 Sl+ 21:28 0:05
/root/miniconda3/envs/xxx/bin/python3.10 -c from multiprocessing.spawn import
spawn_main; spawn_main(tracker_fd=8, pipe_handle=10) --multiprocessing-fork
root 2656201 0.3 1.4 488744 232272 pts/0 Sl+ 21:28 0:05
/root/miniconda3/envs/xxx/bin/python3.10 -c from multiprocessing.spawn import
spawn_main; spawn_main(tracker_fd=8, pipe_handle=14) --multiprocessing-fork
root 2656202 0.3 1.3 548744 221488 pts/0 Sl+ 21:28 0:05
/root/miniconda3/envs/xxx/bin/python3.10 -c from multiprocessing.spawn import
spawn_main; spawn_main(tracker_fd=8, pipe_handle=18) --multiprocessing-fork
root 2656203 0.3 1.3 551072 223920 pts/0 Sl+ 21:28 0:05
/root/miniconda3/envs/xxx/bin/python3.10 -c from multiprocessing.spawn import
spawn_main; spawn_main(tracker_fd=8, pipe_handle=24) --multiprocessing-fork
root 2656706 3.1 1.0 212584 171700 pts/4 S+ 21:31 0:46
/root/miniconda3/envs/xxx/bin/python3.10 /root/miniconda3/envs/xxx/bin/airflow
scheduler
systemd+ 2656711 1.0 0.1 226844 22560 ? Ss 21:31 0:15 postgres:
postgres airflow 172.20.0.1(55568) idle
root 2656786 0.8 1.0 279012 166460 pts/6 Sl+ 21:31 0:13
/root/miniconda3/envs/xxx/bin/python3.10 /root/miniconda3/envs/xxx/bin/airflow
dag-processor
root 2657018 0.0 0.9 204676 147136 pts/4 S+ 21:31 0:00 airflow
worker -- LocalExecutor: <idle>
root 2657019 0.0 0.9 205468 147964 pts/4 S+ 21:31 0:00 airflow
worker -- LocalExecutor: <idle>
root 2657511 0.7 0.9 200436 159288 pts/8 S+ 21:32 0:09
/root/miniconda3/envs/xxx/bin/python3.10 /root/miniconda3/envs/xxx/bin/airflow
triggerer
root 2657555 0.1 0.8 198196 135840 pts/8 S+ 21:32 0:02
/root/miniconda3/envs/xxx/bin/python3.10 /root/miniconda3/envs/xxx/bin/airflow
triggerer
```
GitHub link: https://github.com/apache/airflow/discussions/53494
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