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[GSOC] Support for various Parameter distributions in Katib (#2334)
Signed-off-by: Shashank Mittal <[email protected]> modified feasibleSpace refactored proposal based on comments comparison table updated extra heading removed
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| # Proposal for Supporting various parameter distributions in Katib | ||
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| ## Summary | ||
| The goal of this project is to enhance the existing Katib Experiment APIs to support various parameter distributions such as uniform, log-uniform, and qlog-uniform. Then extend the suggestion services to be able to configure distributions for search space using libraries provided in each framework. | ||
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| ## Motivation | ||
| Currently, [Katib](https://github.com/kubeflow/katib) is limited to supporting only uniform distribution for integer, float, and categorical hyperparameters. By introducing additional distributions, Katib will become more flexible and powerful in conducting hyperparameter optimization tasks. | ||
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| A Data Scientist requires Katib to support multiple hyperparameter distributions, such as log-uniform, normal, and log-normal, in addition to the existing uniform distribution. This enhancement is crucial for more flexible and precise hyperparameter optimization. For instance, learning rates often benefit from a log-uniform distribution because small values can significantly impact performance. Similarly, normal distributions are useful for parameters that are expected to vary around a central value. | ||
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| ### Goals | ||
| - Add `Distribution` field to `FeasibleSpace` alongside `ParameterType`. | ||
| - Support for the log-uniform, normal, and log-normal Distributions. | ||
| - Update the Experiment and gRPC API to support `Distribution`. | ||
| - Update logic to handle the new parameter distributions for each suggestion service (e.g., Optuna, Hyperopt). | ||
| - Extend the Python SDK to support the new `Distribution` field. | ||
| ### Non-Goals | ||
| - This proposal do not aim to create new version for CRD APIs. | ||
| - This proposal do not aim to make the necessary Katib UI changes. | ||
| - No changes will be made to the core optimization algorithms beyond supporting new distributions. | ||
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| ## Proposal | ||
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| ### Parameter Distribution Comparison Table | ||
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| | Distribution Type | Hyperopt | Optuna | Ray Tune | Nevergrad | | ||
| |-------------------------------|-----------------------|-------------------------------------------------|-----------------------|---------------------------------------------| | ||
| | **Uniform Continuous** | `hp.uniform` | `FloatDistribution` | `tune.uniform` | `p.Scalar` with uniform transformation | | ||
| | **Quantized Uniform** | `hp.quniform` | `DiscreteUniformDistribution` (deprecated) | `tune.quniform` | `p.Scalar` with uniform and step specified | | ||
| | **Log Uniform** | `hp.loguniform` | `LogUniformDistribution` (deprecated) | `tune.loguniform` | `p.Log` with uniform transformation | | ||
| | **Uniform Integer** | `hp.randint` or quantized distributions with step size `q` set to 1 | `IntDistribution` | `tune.randint` | `p.Scalar` with integer transformation | | ||
| | **Categorical** | `hp.choice` | `CategoricalDistribution` | `tune.choice` | `p.Choice` | | ||
| | **Quantized Log Uniform** | `hp.qloguniform` | Custom Implementation | `tune.qloguniform` | `p.Log` with uniform and step specified | | ||
| | **Normal** | `hp.normal` | (Not directly supported) | `tune.randn` | (Not directly supported) | | ||
| | **Quantized Normal** | `hp.qnormal` | (Not directly supported) | `tune.qrandn` | (Not directly supported) | | ||
| | **Log Normal** | `hp.lognormal` | (Not directly supported) | (Use custom transformation in `tune.randn`) | (Not directly supported) | | ||
| | **Quantized Log Normal** | `hp.qlognormal` | (Not directly supported) | (Use custom transformation in `tune.qrandn`) | (Not directly supported) | | ||
| | **Quantized Integer** | `hp.quniformint` | `IntUniformDistribution` (deprecated) | | `p.Scalar` with integer and step specified | | ||
| | **Log Integer** | | `IntLogUniformDistribution` (deprecated) | `tune.lograndint` | `p.Scalar` with log-integer transformation | | ||
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| - Note: | ||
| In `Nevergrad`, parameter types like `p.Scalar`, `p.Log`, and `p.Choice` are mapped to corresponding `Hyperopt` search space definitions like `hp.uniform`, `hp.loguniform`, and `hp.choice` using internal functions to convert parameter bounds and distributions. | ||
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| ## API Design | ||
| ### FeasibleSpace | ||
| Feasible space for optimization. | ||
| Int and Double type use Max/Min. | ||
| Discrete and Categorical type use List. | ||
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| | Field | Type | Label | Description | | ||
| | ----- | ---- | ----- | ----------- | | ||
| | max | [string](#string) | | Max Value | | ||
| | min | [string](#string) | | Minimum Value | | ||
| | list | [string](#string) | repeated | List of Values. | | ||
| | step | [string](#string) | | Step for double or int parameter or q for quantization| | ||
| | distribution | [Distribution](#api-v1-beta1-Distribution) | | Type of the Distribution. | | ||
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| <a name="api-v1-beta1-Distribution"></a> | ||
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| ### Distribution | ||
| - Types of value for HyperParameter Distributions. | ||
| - We add the `distribution` field to represent the hyperparameters search space rather than [`ParameterType`](https://github.com/kubeflow/katib/blob/2c575227586ff1c03cf6b5190d066e2f3061a404/pkg/apis/controller/experiments/v1beta1/experiment_types.go#L199-L207). | ||
| - The `distribution` allows users to configure more granular search space customizations. | ||
| - In this enhancement, we would propose the following 4 distributions: | ||
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| | Name | Number | Description | | ||
| | ---- | ------ | ----------- | | ||
| | UNIFORM | 0 | Continuous uniform distribution. Samples values evenly between a minimum and maximum value. Use "Max/Min". Use "Step" for `q`. | | ||
| | LOGUNIFORM | 1 | Samples values such that their logarithm is uniformly distributed. Use "Max/Min". Use "Step" for `q`. | | ||
| | NORMAL | 2 | Normal (Gaussian) distribution type. Samples values according to a normal distribution characterized by a mean and standard deviation. Use "Max/Min". Use "Step" for `q`. | | ||
| | LOGNORMAL | 3 | Log-normal distribution type. Samples values such that their logarithm is normally distributed. Use "Max/Min". Use "Step" for `q`. | | ||
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| ## Experiment API changes | ||
| Scope: `pkg/apis/controller/experiments/v1beta1/experiment_types.go` | ||
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| ```go | ||
| type ParameterSpec struct { | ||
| Name string `json:"name,omitempty"` | ||
| ParameterType ParameterType `json:"parameterType,omitempty"` | ||
| FeasibleSpace FeasibleSpace `json:"feasibleSpace,omitempty"` | ||
| } | ||
| ``` | ||
| - Adding new field `Distribution` to `FeasibleSpace` | ||
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| - The `Step` field can be used to define quantization steps for uniform or log-uniform distributions, effectively covering q-quantization requirements. | ||
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| Updated `FeasibleSpace` struct | ||
| ```diff | ||
| type FeasibleSpace struct { | ||
| Max string `json:"max,omitempty"` | ||
| Min string `json:"min,omitempty"` | ||
| List []string `json:"list,omitempty"` | ||
| Step string `json:"step,omitempty"` // Step can be used to define q-quantization | ||
| + Distribution Distribution `json:"distribution,omitempty"` // Added Distribution field | ||
| } | ||
| ``` | ||
| - New Field Description: `Distribution` | ||
| - Type: `Distribution` | ||
| - Description: The Distribution field specifies the type of statistical distribution to be applied to the parameter. This allows the definition of various distributions, such as uniform, log-uniform, or other supported types. | ||
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| - Defining `Distribution` type | ||
| ```go | ||
| type Distribution string | ||
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| const ( | ||
| DistributionUniform Distribution = "uniform" | ||
| DistributionLogUniform Distribution = "logUniform" | ||
| DistributionNormal Distribution = "normal" | ||
| DistributionLogNormal Distribution = "logNormal" | ||
| ) | ||
| ``` | ||
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| ## gRPC API changes | ||
| Scope: `pkg/apis/manager/v1beta1/api.proto` | ||
| - Add the `Distribution` field to the `FeasibleSpace` message | ||
| ```diff | ||
| /** | ||
| * Feasible space for optimization. | ||
| * Int and Double type use Max/Min. | ||
| * Discrete and Categorical type use List. | ||
| */ | ||
| message FeasibleSpace { | ||
| string max = 1; /// Max Value | ||
| string min = 2; /// Minimum Value | ||
| repeated string list = 3; /// List of Values. | ||
| string step = 4; /// Step for double or int parameter | ||
| + Distribution distribution = 4; // Distribution of the parameter. | ||
| } | ||
| ``` | ||
| - Define the `Distribution` enum | ||
| ``` | ||
| /** | ||
| * Distribution types for HyperParameter. | ||
| */ | ||
| enum Distribution { | ||
| UNIFORM = 0; | ||
| LOG_UNIFORM = 1; | ||
| NORMAL = 2; | ||
| LOG_NORMAL = 3; | ||
| } | ||
| ``` | ||
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| ## Suggestion Service Logic | ||
| - For each suggestion service (e.g., Optuna, Hyperopt), the logic will be updated to handle the new parameter distributions. | ||
| - This involves modifying the conversion functions to map Katib distributions to the corresponding framework-specific distributions. | ||
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| #### Optuna | ||
| ref: https://optuna.readthedocs.io/en/stable/reference/distributions.html | ||
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| For example: | ||
| - Update the `_get_optuna_search_space` for new Distributions. | ||
| scope: `pkg/suggestion/v1beta1/optuna/base_service.py` | ||
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| #### Goptuna | ||
| ref: https://github.com/c-bata/goptuna/blob/2245ddd9e8d1edba750839893c8a618f852bc1cf/distribution.go | ||
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| #### Hyperopt | ||
| ref: http://hyperopt.github.io/hyperopt/getting-started/search_spaces/#parameter-expressions | ||
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| #### Ray-tune | ||
| ref: https://docs.ray.io/en/latest/tune/api/search_space.html | ||
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| ## Python SDK | ||
| Extend the Python SDK to support the new `Distribution` field. | ||
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