Abstract intensifier

smac.intensifier.abstract_intensifier

AbstractIntensifier

AbstractIntensifier(
    scenario: Scenario,
    n_seeds: int | None = None,
    max_config_calls: int | None = None,
    max_incumbents: int = 10,
    seed: int | None = None,
)

Abstract implementation of an intensifier supporting multi-fidelity, multi-objective, and multi-threading. The abstract intensifier keeps track of the incumbent, which is updated everytime the runhistory changes.

Parameters

n_seeds : int | None, defaults to None How many seeds to use for each instance. It is used in the abstract intensifier to determine validation trials. max_config_calls : int, defaults to None Maximum number of configuration evaluations. Basically, how many instance-seed keys should be max evaluated for a configuration. It is used in the abstract intensifier to determine validation trials. max_incumbents : int, defaults to 10 How many incumbents to keep track of in the case of multi-objective. seed : int, defaults to None Internal seed used for random events like shuffle seeds.

Source code in smac/intensifier/abstract_intensifier.py

def __init__(
    self,
    scenario: Scenario,
    n_seeds: int | None = None,
    max_config_calls: int | None = None,
    max_incumbents: int = 10,
    seed: int | None = None,
):
    self._scenario = scenario
    self._config_selector: ConfigSelector | None = None
    self._config_generator: Iterator[ConfigSelector] | None = None
    self._runhistory: RunHistory | None = None

    if seed is None:
        seed = self._scenario.seed

    self._seed = seed
    self._rng = np.random.RandomState(seed)

    # Internal variables
    self._n_seeds = n_seeds
    self._max_config_calls = max_config_calls
    self._max_incumbents = max_incumbents
    self._used_walltime_func: Callable | None = None

    # Reset everything
    self.reset()

config_generator property

config_generator: Iterator[Configuration]

Based on the configuration selector, an iterator is returned that generates configurations.

config_selector property writable

config_selector: ConfigSelector

The configuration selector for the intensifier.

incumbents_changed property

incumbents_changed: int

How often the incumbents have changed.

meta property

meta: dict[str, Any]

Returns the meta data of the created object.

runhistory property writable

runhistory: RunHistory

Runhistory of the intensifier.

trajectory property

trajectory: list[TrajectoryItem]

Returns the trajectory (changes of incumbents) of the optimization run.

used_walltime property writable

used_walltime: float

Returns used wallclock time.

uses_budgets abstractmethod property

uses_budgets: bool

If the intensifier needs to make use of budgets.

uses_instances abstractmethod property

uses_instances: bool

If the intensifier needs to make use of instances.

uses_seeds abstractmethod property

uses_seeds: bool

If the intensifier needs to make use of seeds.

__iter__ abstractmethod

__iter__() -> Iterator[TrialInfo]

Main loop of the intensifier. This method always returns a TrialInfo object, although the intensifier algorithm may need to wait for the result of the trial. Please refer to a specific intensifier to get more information.

Source code in smac/intensifier/abstract_intensifier.py

@abstractmethod
def __iter__(self) -> Iterator[TrialInfo]:
    """Main loop of the intensifier. This method always returns a TrialInfo object, although the intensifier
    algorithm may need to wait for the result of the trial. Please refer to a specific
    intensifier to get more information.
    """
    raise NotImplementedError

__post_init__

__post_init__() -> None

Fills self._tf_seeds and self._tf_instances. Moreover, the incumbents are updated.

Source code in smac/intensifier/abstract_intensifier.py

def __post_init__(self) -> None:
    """Fills ``self._tf_seeds`` and ``self._tf_instances``. Moreover, the incumbents are updated."""
    rh = self.runhistory

    # Validate runhistory: Are seeds/instances/budgets used?
    # Add seed/instance/budget to the cache
    for k in rh.keys():
        if self.uses_seeds:
            if k.seed is None:
                raise ValueError("Trial contains no seed information but intensifier expects seeds to be used.")

            if k.seed not in self._tf_seeds:
                self._tf_seeds.append(k.seed)

        if self.uses_instances:
            if self._scenario.instances is None and k.instance is not None:
                raise ValueError(
                    "Scenario does not specify any instances but found instance information in runhistory."
                )

            if self._scenario.instances is not None and k.instance not in self._scenario.instances:
                raise ValueError(
                    "Instance information in runhistory is not part of the defined instances in scenario."
                )

            if k.instance not in self._tf_instances:
                self._tf_instances.append(k.instance)

        if self.uses_budgets:
            if k.budget is None:
                raise ValueError("Trial contains no budget information but intensifier expects budgets to be used.")

            if k.budget not in self._tf_budgets:
                self._tf_budgets.append(k.budget)

    # Add all other instances to ``_tf_instances``
    # Behind idea: Prioritize instances that are found in the runhistory
    if (instances := self._scenario.instances) is not None:
        for inst in instances:
            if inst not in self._tf_instances:
                self._tf_instances.append(inst)

    if len(self._tf_instances) == 0:
        self._tf_instances = [None]

    if len(self._tf_budgets) == 0:
        self._tf_budgets = [None]

    # Update our incumbents here
    for config in rh.get_configs():
        self.update_incumbents(config)

get_callback

get_callback() -> Callback

The intensifier makes use of a callback to efficiently update the incumbent based on the runhistory (every time new information is available). Moreover, incorporating the callback here allows developers more options in the future.

Source code in smac/intensifier/abstract_intensifier.py

def get_callback(self) -> Callback:
    """The intensifier makes use of a callback to efficiently update the incumbent based on the runhistory
    (every time new information is available). Moreover, incorporating the callback here allows developers
    more options in the future.
    """

    class RunHistoryCallback(Callback):
        def __init__(self, intensifier: AbstractIntensifier):
            self.intensifier = intensifier

        def on_tell_end(self, smbo: smac.main.smbo.SMBO, info: TrialInfo, value: TrialValue) -> None:
            self.intensifier.update_incumbents(info.config)

    return RunHistoryCallback(self)

get_incumbent

get_incumbent() -> Configuration | None

Returns the current incumbent in a single-objective setting.

Source code in smac/intensifier/abstract_intensifier.py

def get_incumbent(self) -> Configuration | None:
    """Returns the current incumbent in a single-objective setting."""
    if self._scenario.count_objectives() > 1:
        raise ValueError("Cannot get a single incumbent for multi-objective optimization.")

    if len(self._incumbents) == 0:
        return None

    assert len(self._incumbents) == 1
    return self._incumbents[0]

get_incumbent_instance_seed_budget_key_differences

get_incumbent_instance_seed_budget_key_differences(
    compare: bool = False,
) -> list[InstanceSeedBudgetKey]

There are situations in which incumbents are evaluated on more trials than others. This method returns the instances that are not part of the lowest intersection of instances for all incumbents.

Source code in smac/intensifier/abstract_intensifier.py

def get_incumbent_instance_seed_budget_key_differences(self, compare: bool = False) -> list[InstanceSeedBudgetKey]:
    """There are situations in which incumbents are evaluated on more trials than others. This method returns the
    instances that are not part of the lowest intersection of instances for all incumbents.
    """
    incumbents = self.get_incumbents()

    if len(incumbents) > 0:
        # We want to calculate the differences so that we can evaluate the other incumbents on the same instances
        incumbent_isb_keys = [self.get_instance_seed_budget_keys(incumbent, compare) for incumbent in incumbents]

        if len(incumbent_isb_keys) <= 1:
            return []

        # Compute the actual differences
        intersection_isb_keys = set.intersection(*map(set, incumbent_isb_keys))  # type: ignore
        union_isb_keys = set.union(*map(set, incumbent_isb_keys))  # type: ignore
        incumbent_isb_keys = list(union_isb_keys - intersection_isb_keys)  # type: ignore

        if len(incumbent_isb_keys) == 0:
            return []

        return incumbent_isb_keys  # type: ignore

    return []

get_incumbent_instance_seed_budget_keys

get_incumbent_instance_seed_budget_keys(
    compare: bool = False,
) -> list[InstanceSeedBudgetKey]

Find the lowest intersection of instance-seed-budget keys for all incumbents.

Source code in smac/intensifier/abstract_intensifier.py

def get_incumbent_instance_seed_budget_keys(self, compare: bool = False) -> list[InstanceSeedBudgetKey]:
    """Find the lowest intersection of instance-seed-budget keys for all incumbents."""
    incumbents = self.get_incumbents()

    if len(incumbents) > 0:
        # We want to calculate the smallest set of trials that is used by all incumbents
        # Reason: We can not fairly compare otherwise
        incumbent_isb_keys = [self.get_instance_seed_budget_keys(incumbent, compare) for incumbent in incumbents]
        instances = list(set.intersection(*map(set, incumbent_isb_keys)))  # type: ignore

        return instances  # type: ignore

    return []

get_incumbents

get_incumbents(
    sort_by: str | None = None,
) -> list[Configuration]

Returns the incumbents (points on the pareto front) of the runhistory as copy. In case of a single-objective optimization, only one incumbent (if is) is returned.

Returns

configs : list[Configuration] The configs of the Pareto front. sort_by : str, defaults to None Sort the trials by cost (lowest cost first) or num_trials (config with lowest number of trials first).

Source code in smac/intensifier/abstract_intensifier.py

def get_incumbents(self, sort_by: str | None = None) -> list[Configuration]:
    """Returns the incumbents (points on the pareto front) of the runhistory as copy. In case of a single-objective
    optimization, only one incumbent (if is) is returned.

    Returns
    -------
    configs : list[Configuration]
        The configs of the Pareto front.
    sort_by : str, defaults to None
        Sort the trials by ``cost`` (lowest cost first) or ``num_trials`` (config with lowest number of trials
        first).
    """
    rh = self.runhistory

    if sort_by == "cost":
        return list(sorted(self._incumbents, key=lambda config: rh._cost_per_config[rh.get_config_id(config)]))
    elif sort_by == "num_trials":
        return list(sorted(self._incumbents, key=lambda config: len(rh.get_trials(config))))
    elif sort_by is None:
        return list(self._incumbents)
    else:
        raise ValueError(f"Unknown sort_by value: {sort_by}.")

get_instance_seed_budget_keys

get_instance_seed_budget_keys(
    config: Configuration, compare: bool = False
) -> list[InstanceSeedBudgetKey]

Returns the instance-seed-budget keys for a given configuration. This method is used for updating the incumbents and might differ for different intensifiers. For example, if incumbents should only be compared on the highest observed budgets.

Source code in smac/intensifier/abstract_intensifier.py

def get_instance_seed_budget_keys(
    self, config: Configuration, compare: bool = False
) -> list[InstanceSeedBudgetKey]:
    """Returns the instance-seed-budget keys for a given configuration. This method is *used for
    updating the incumbents* and might differ for different intensifiers. For example, if incumbents should only
    be compared on the highest observed budgets.
    """
    return self.runhistory.get_instance_seed_budget_keys(config, highest_observed_budget_only=False)

get_instance_seed_keys_of_interest

get_instance_seed_keys_of_interest(
    *, validate: bool = False, seed: int | None = None
) -> list[InstanceSeedKey]

Returns a list of instance-seed keys. Considers seeds and instances from the runhistory (self._tf_seeds and self._tf_instances). If no seeds or instances were found, new seeds and instances are generated based on the global intensifier seed.

Warning

The passed seed is only used for validation. For training, the global intensifier seed is used.

Parameters

validate : bool, defaults to False Whether to get validation trials or training trials. The only difference lies in different seeds. seed : int | None, defaults to None The seed used for the validation trials.

Returns

instance_seed_keys : list[InstanceSeedKey] Instance-seed keys of interest.

Source code in smac/intensifier/abstract_intensifier.py

def get_instance_seed_keys_of_interest(
    self,
    *,
    validate: bool = False,
    seed: int | None = None,
) -> list[InstanceSeedKey]:
    """Returns a list of instance-seed keys. Considers seeds and instances from the
    runhistory (``self._tf_seeds`` and ``self._tf_instances``). If no seeds or instances were found, new
    seeds and instances are generated based on the global intensifier seed.

    Warning
    -------
    The passed seed is only used for validation. For training, the global intensifier seed is used.

    Parameters
    ----------
    validate : bool, defaults to False
        Whether to get validation trials or training trials. The only difference lies in different seeds.
    seed : int | None, defaults to None
        The seed used for the validation trials.

    Returns
    -------
    instance_seed_keys : list[InstanceSeedKey]
        Instance-seed keys of interest.
    """
    if self._runhistory is None:
        raise RuntimeError("Please set the runhistory before calling this method.")

    if len(self._tf_instances) == 0:
        raise RuntimeError("Please call __post_init__ before calling this method.")

    if seed is None:
        seed = 0

    # We cache the instance-seed keys for efficiency and consistency reasons
    if (self._instance_seed_keys is None and not validate) or (
        self._instance_seed_keys_validation is None and validate
    ):
        instance_seed_keys: list[InstanceSeedKey] = []
        if validate:
            rng = np.random.RandomState(seed)
        else:
            rng = self._rng

        i = 0
        while True:
            found_enough_configs = (
                self._max_config_calls is not None and len(instance_seed_keys) >= self._max_config_calls
            )
            used_enough_seeds = self._n_seeds is not None and i >= self._n_seeds

            if found_enough_configs or used_enough_seeds:
                break

            if validate:
                next_seed = int(rng.randint(low=0, high=MAXINT, size=1)[0])
            else:
                try:
                    next_seed = self._tf_seeds[i]
                    logger.info(f"Added existing seed {next_seed} from runhistory to the intensifier.")
                except IndexError:
                    # Use global random generator for a new seed and mark it so it will be reused for another config
                    next_seed = int(rng.randint(low=0, high=MAXINT, size=1)[0])

                    # This line here is really important because we don't want to add the same seed twice
                    if next_seed in self._tf_seeds:
                        continue

                    self._tf_seeds.append(next_seed)
                    logger.debug(f"Added a new random seed {next_seed} to the intensifier.")

            # If no instances are used, tf_instances includes None
            for instance in self._tf_instances:
                instance_seed_keys.append(InstanceSeedKey(instance, next_seed))

            # Only use one seed in deterministic case
            if self._scenario.deterministic:
                logger.info("Using only one seed for deterministic scenario.")
                break

            # Seed counter
            i += 1

        # Now we cut so that we only have max_config_calls instance_seed_keys
        # We favor instances over seeds here: That makes sure we always work with the same instance/seed pairs
        if self._max_config_calls is not None:
            if len(instance_seed_keys) > self._max_config_calls:
                instance_seed_keys = instance_seed_keys[: self._max_config_calls]
                logger.info(f"Cut instance-seed keys to {self._max_config_calls} entries.")

        # Set it globally
        if not validate:
            self._instance_seed_keys = instance_seed_keys
        else:
            self._instance_seed_keys_validation = instance_seed_keys

    if not validate:
        assert self._instance_seed_keys is not None
        instance_seed_keys = self._instance_seed_keys
    else:
        assert self._instance_seed_keys_validation is not None
        instance_seed_keys = self._instance_seed_keys_validation

    return instance_seed_keys.copy()

get_rejected_configs

get_rejected_configs() -> list[Configuration]

Returns rejected configurations when racing against the incumbent failed.

Source code in smac/intensifier/abstract_intensifier.py

def get_rejected_configs(self) -> list[Configuration]:
    """Returns rejected configurations when racing against the incumbent failed."""
    configs = []
    for rejected_config_id in self._rejected_config_ids:
        configs.append(self.runhistory._ids_config[rejected_config_id])

    return configs

get_state

get_state() -> dict[str, Any]

The current state of the intensifier. Used to restore the state of the intensifier when continuing a run.

Source code in smac/intensifier/abstract_intensifier.py

def get_state(self) -> dict[str, Any]:
    """The current state of the intensifier. Used to restore the state of the intensifier when continuing a run."""
    return {}

get_trials_of_interest

get_trials_of_interest(
    config: Configuration,
    *,
    validate: bool = False,
    seed: int | None = None
) -> list[TrialInfo]

Returns the trials of interest for a given configuration. Expands the keys from get_instance_seed_keys_of_interest with the config.

Source code in smac/intensifier/abstract_intensifier.py

def get_trials_of_interest(
    self,
    config: Configuration,
    *,
    validate: bool = False,
    seed: int | None = None,
) -> list[TrialInfo]:
    """Returns the trials of interest for a given configuration.
    Expands the keys from ``get_instance_seed_keys_of_interest`` with the config.
    """
    is_keys = self.get_instance_seed_keys_of_interest(validate=validate, seed=seed)

    trials = []
    for key in is_keys:
        trials.append(TrialInfo(config=config, instance=key.instance, seed=key.seed))

    return trials

load

load(filename: str | Path) -> None

Loads the latest state of the intensifier including the incumbents and trajectory.

Source code in smac/intensifier/abstract_intensifier.py

def load(self, filename: str | Path) -> None:
    """Loads the latest state of the intensifier including the incumbents and trajectory."""
    if isinstance(filename, str):
        filename = Path(filename)

    try:
        with open(filename) as fp:
            data = json.load(fp)
    except Exception as e:
        logger.warning(
            f"Encountered exception {e} while reading runhistory from {filename}. Not adding any trials!"
        )
        return

    # We reset the intensifier and then reset the runhistory
    self.reset()
    if self._runhistory is not None:
        self.runhistory = self._runhistory

    self._incumbents = [self.runhistory.get_config(config_id) for config_id in data["incumbent_ids"]]
    self._incumbents_changed = data["incumbents_changed"]
    self._rejected_config_ids = data["rejected_config_ids"]
    self._trajectory = [TrajectoryItem(**item) for item in data["trajectory"]]
    self.set_state(data["state"])

reset

reset() -> None

Reset the internal variables of the intensifier.

Source code in smac/intensifier/abstract_intensifier.py

def reset(self) -> None:
    """Reset the internal variables of the intensifier."""
    self._tf_seeds: list[int] = []
    self._tf_instances: list[str | None] = []
    self._tf_budgets: list[float | None] = []
    self._instance_seed_keys: list[InstanceSeedKey] | None = None
    self._instance_seed_keys_validation: list[InstanceSeedKey] | None = None

    # Incumbent variables
    self._incumbents: list[Configuration] = []
    self._incumbents_changed = 0
    self._rejected_config_ids: list[int] = []
    self._trajectory: list[TrajectoryItem] = []

save

save(filename: str | Path) -> None

Saves the current state of the intensifier. In addition to the state (retrieved by get_state), this method also saves the incumbents and trajectory.

Source code in smac/intensifier/abstract_intensifier.py

def save(self, filename: str | Path) -> None:
    """Saves the current state of the intensifier. In addition to the state (retrieved by ``get_state``), this
    method also saves the incumbents and trajectory.
    """
    if isinstance(filename, str):
        filename = Path(filename)

    assert str(filename).endswith(".json")
    filename.parent.mkdir(parents=True, exist_ok=True)

    data = {
        "incumbent_ids": [self.runhistory.get_config_id(config) for config in self._incumbents],
        "rejected_config_ids": self._rejected_config_ids,
        "incumbents_changed": self._incumbents_changed,
        "trajectory": [dataclasses.asdict(item) for item in self._trajectory],
        "state": self.get_state(),
    }

    with open(filename, "w") as fp:
        json.dump(data, fp, indent=2, cls=NumpyEncoder)

set_state

set_state(state: dict[str, Any]) -> None

Sets the state of the intensifier. Used to restore the state of the intensifier when continuing a run.

Source code in smac/intensifier/abstract_intensifier.py

def set_state(self, state: dict[str, Any]) -> None:
    """Sets the state of the intensifier. Used to restore the state of the intensifier when continuing a run."""
    pass

update_incumbents

update_incumbents(config: Configuration) -> None

Updates the incumbents. This method is called everytime a trial is added to the runhistory. Since only the affected config and the current incumbents are used, this method is very efficient. Furthermore, a configuration is only considered incumbent if it has a better performance on all incumbent instances.

Crucially, if there is no incumbent (at the start) then, the first configuration assumes incumbent status. For the next configuration, we need to check if the configuration is better on all instances that have been evaluated for the incumbent. If this is the case, then we can replace the incumbent. Otherwise, a) we need to requeue the config to obtain the missing instance-seed-budget combination or b) mark this configuration as inferior ("rejected") to not consider it again. The comparison behaviour is controlled by self.get_instance_seed_budget_keys() and self.get_incumbent_instance_seed_budget_keys().

Notably, this method is written to support both multi-fidelity and multi-objective optimization. While the get_instance_seed_budget_keys() method and self.get_incumbent_instance_seed_budget_keys() are used for the multi-fidelity behaviour, calculate_pareto_front() is used as a hard coded way to support multi-objective optimization, including the single objective as special case. calculate_pareto_front() is called on the set of all (in case of MO) incumbents amended with the challenger configuration, provided it has a sufficient overlap in seed-instance-budget combinations.

Lastly, if we have a self._max_incumbents and the pareto front provides more than this specified amount, we cut the incumbents using crowding distance.

Source code in smac/intensifier/abstract_intensifier.py

def update_incumbents(self, config: Configuration) -> None:
    """Updates the incumbents. This method is called everytime a trial is added to the runhistory. Since only
    the affected config and the current incumbents are used, this method is very efficient. Furthermore, a
    configuration is only considered incumbent if it has a better performance on all incumbent instances.

    Crucially, if there is no incumbent (at the start) then, the first configuration assumes
    incumbent status. For the next configuration, we need to check if the configuration
    is better on all instances that have been evaluated for the incumbent. If this is the
    case, then we can replace the incumbent. Otherwise, a) we need to requeue the config to
    obtain the missing instance-seed-budget combination or b) mark this configuration as
    inferior ("rejected") to not consider it again. The comparison behaviour is controlled by
    self.get_instance_seed_budget_keys() and self.get_incumbent_instance_seed_budget_keys().

    Notably, this method is written to support both multi-fidelity and multi-objective
    optimization. While the get_instance_seed_budget_keys() method and
    self.get_incumbent_instance_seed_budget_keys() are used for the multi-fidelity behaviour,
    calculate_pareto_front() is used as a hard coded way to support multi-objective
    optimization, including the single objective as special case. calculate_pareto_front()
    is called on the set of all (in case of MO) incumbents amended with the challenger
    configuration, provided it has a sufficient overlap in seed-instance-budget combinations.

    Lastly, if we have a self._max_incumbents and the pareto front provides more than this
    specified amount, we cut the incumbents using crowding distance.
    """
    rh = self.runhistory

    # What happens if a config was rejected, but it appears again? Give it another try even if it
    # has already been evaluated? Yes!

    # Associated trials and id
    config_isb_keys = self.get_instance_seed_budget_keys(config)
    config_id = rh.get_config_id(config)
    config_hash = get_config_hash(config)

    # We skip updating incumbents if no instances are available
    # Note: This is especially the case if trials of a config are still running
    # because if trials are running, the runhistory does not update the trials in the fast data structure
    if len(config_isb_keys) == 0:
        logger.debug(f"No relevant instances evaluated for config {config_hash}. Updating incumbents is skipped.")
        return

    # Now we get the incumbents and see which trials have been used
    incumbents = self.get_incumbents()
    incumbent_ids = [rh.get_config_id(c) for c in incumbents]
    # Find the lowest intersection of instance-seed-budget keys for all incumbents.
    incumbent_isb_keys = self.get_incumbent_instance_seed_budget_keys()

    # Save for later
    previous_incumbents = incumbents.copy()
    previous_incumbent_ids = incumbent_ids.copy()

    # Little sanity check here for consistency
    if len(incumbents) > 0:
        assert incumbent_isb_keys is not None
        assert len(incumbent_isb_keys) > 0

    # If there are no incumbents at all, we just use the new config as new incumbent
    # Problem: We can add running incumbents
    if len(incumbents) == 0:  # incumbent_isb_keys is None and len(incumbents) == 0:
        logger.info(f"Added config {config_hash} as new incumbent because there are no incumbents yet.")
        self._update_trajectory([config])

        # Nothing else to do
        return

    # Comparison keys
    # This one is a bit tricky: We would have problems if we compare with budgets because we might have different
    # scenarios (depending on the incumbent selection specified in Successive Halving).
    # 1) Any budget/highest observed budget: We want to get rid of the budgets because if we know it is calculated
    # on the same instance-seed already then we are ready to go. Imagine we would check for the same budgets,
    # then the configs can not be compared although the user does not care on which budgets configurations have
    # been evaluated.
    # 2) Highest budget: We only want to compare the configs if they are evaluated on the highest budget.
    # Here we do actually care about the budgets. Please see the ``get_instance_seed_budget_keys`` method from
    # Successive Halving to get more information.
    # Noitce: compare=True only takes effect when subclass implemented it. -- e.g. in SH it
    # will remove the budgets from the keys.
    config_isb_comparison_keys = self.get_instance_seed_budget_keys(config, compare=True)
    # Find the lowest intersection of instance-seed-budget keys for all incumbents.
    config_incumbent_isb_comparison_keys = self.get_incumbent_instance_seed_budget_keys(compare=True)

    # Now we have to check if the new config has been evaluated on the same keys as the incumbents
    if not all([key in config_isb_comparison_keys for key in config_incumbent_isb_comparison_keys]):
        # We can not tell if the new config is better/worse than the incumbents because it has not been
        # evaluated on the necessary trials
        logger.debug(
            f"Could not compare config {config_hash} with incumbents because it's evaluated on "
            f"different trials."
        )

        # The config has to go to a queue now as it is a challenger and a potential incumbent
        return
    else:
        # If all instances are available and the config is incumbent and even evaluated on more trials
        # then there's nothing we can do
        if config in incumbents and len(config_isb_keys) > len(incumbent_isb_keys):
            logger.debug(
                "Config is already an incumbent but can not be compared to other incumbents because "
                "the others are missing trials."
            )
            return

    # Add config to incumbents so that we compare only the new config and existing incumbents
    if config not in incumbents:
        incumbents.append(config)
        incumbent_ids.append(config_id)

    # Now we get all instance-seed-budget keys for each incumbent (they might be different when using budgets)
    all_incumbent_isb_keys = []
    for incumbent in incumbents:
        all_incumbent_isb_keys.append(self.get_instance_seed_budget_keys(incumbent))

    # We compare the incumbents now and only return the ones on the pareto front
    new_incumbents = calculate_pareto_front(rh, incumbents, all_incumbent_isb_keys)
    new_incumbent_ids = [rh.get_config_id(c) for c in new_incumbents]

    if len(previous_incumbents) == len(new_incumbents):
        if previous_incumbents == new_incumbents:
            # No changes in the incumbents, we need this clause because we can't use set difference then
            if config_id in new_incumbent_ids:
                self._remove_rejected_config(config_id)
            else:
                # config worse than incumbents and thus rejected
                self._add_rejected_config(config_id)
            return
        else:
            # In this case, we have to determine which config replaced which incumbent and reject it
            removed_incumbent_id = list(set(previous_incumbent_ids) - set(new_incumbent_ids))[0]
            removed_incumbent_hash = get_config_hash(rh.get_config(removed_incumbent_id))
            self._add_rejected_config(removed_incumbent_id)

            if removed_incumbent_id == config_id:
                logger.debug(
                    f"Rejected config {config_hash} because it is not better than the incumbents on "
                    f"{len(config_isb_keys)} instances."
                )
            else:
                self._remove_rejected_config(config_id)
                logger.info(
                    f"Added config {config_hash} and rejected config {removed_incumbent_hash} as incumbent because "
                    f"it is not better than the incumbents on {len(config_isb_keys)} instances: "
                )
                print_config_changes(rh.get_config(removed_incumbent_id), config, logger=logger)
    elif len(previous_incumbents) < len(new_incumbents):
        # Config becomes a new incumbent; nothing is rejected in this case
        self._remove_rejected_config(config_id)
        logger.info(
            f"Config {config_hash} is a new incumbent. " f"Total number of incumbents: {len(new_incumbents)}."
        )
    else:
        # There might be situations that the incumbents might be removed because of updated cost information of
        # config
        for incumbent in previous_incumbents:
            if incumbent not in new_incumbents:
                self._add_rejected_config(incumbent)
                logger.debug(
                    f"Removed incumbent {get_config_hash(incumbent)} because of the updated costs from config "
                    f"{config_hash}."
                )

    # Cut incumbents: We only want to keep a specific number of incumbents
    # We use the crowding distance for that
    if len(new_incumbents) > self._max_incumbents:
        new_incumbents = sort_by_crowding_distance(rh, new_incumbents, all_incumbent_isb_keys)
        new_incumbents = new_incumbents[: self._max_incumbents]

        # or random?
        # idx = self._rng.randint(0, len(new_incumbents))
        # del new_incumbents[idx]
        # del new_incumbent_ids[idx]

        logger.info(
            f"Removed one incumbent using crowding distance because more than {self._max_incumbents} are "
            "available."
        )

    self._update_trajectory(new_incumbents)