the settings of the webmaster document are as follows

from pytz import utc
from apscheduler.schedulers.background import BackgroundScheduler
from apscheduler.jobstores.mongodb import MongoDBJobStore
from apscheduler.jobstores.sqlalchemy import SQLAlchemyJobStore
from apscheduler.executors.pool import ThreadPoolExecutor, ProcessPoolExecutor


jobstores = {
    "mongo": MongoDBJobStore(),
    "default": SQLAlchemyJobStore(url="sqlite:///jobs.sqlite")
}
executors = {
    "default": ThreadPoolExecutor(20),
    "processpool": ProcessPoolExecutor(5)
}
job_defaults = {
    "coalesce": False,
    "max_instances": 3
}
scheduler = BackgroundScheduler(jobstores=jobstores, executors=executors, job_defaults=job_defaults, timezone=utc)

among them, job_default what does the maximum 3 mean by the official website? the maximum instance limit is 3 coalesce. I don"t understand what it means. Do you perform the same task, such as repetitive tasks, and you can only perform up to three of the same tasks at the same time? Then the merger still doesn"t understand what it means

job_defaults = {
    "coalesce": False,
    "max_instances": 3
}