Motivation

To prevent float precision loss on the storage layer, this PR adds tests for float values.
Related to: #3227 #3327

Description of the changes

Adding precision tests on test_storages.py and test_with_server.py.

Overview of the implementation for the float precision

In the storage layer, the following methods must keep precision of values.

• set_trial_state_values
• set_trial_intermediate_value
• set_trial_param
• set_study_user_attr
• set_study_system_attr
• set_trial_user_attr
• set_trial_system_attr

Note: Outside of the storage layer, to_internal_repr / to_external_repr of distributions must also keep precision. These are tested in test_distributions.py.

These methods handle the following floats:

• set_trial_state_values
  • finite values / inf / -inf
• set_trial_intermediate_value
  • finite values / inf / -inf / nan
• set_trial_param
  • finite values (for FloatDistribution)
  • finite values / inf / -inf / nan (for CategoricalDistribution)
• set_study_user_attr / set_study_system_attr / set_trial_user_attr / set_trial_system_attr
  • finite values / inf / -inf / nan

Storage classes

Note: We assume that there is no precision issues in the encoded JSON string https://docs.python.org/3.13/library/json.html#implementation-limitations.

InMemoryStorage

All values ​​are stored as Python variables so there are no precision issues.

JournalStorage

It dumps all the values ​​into JSON strings and saves them.

RDBStorage

All sqlalchemy.Float specify double-precision.

Note: MySQL cannot handle infinities.

• set_trial_state_values
  • Values are saved as sqlalchemy.Float and TrialValueType.
• set_trial_intermediate_value
  • Values are saved as sqlalchemy.Float and TrialIntermediateValueType.
• set_trial_param
  • FloatDistribution
    • Parameters are saved as sqlalchemy.Float.
    • Distributions are saved as encoded JSON strings.
  • CategoricalDistribution
    • Indexes of parameters are saved as sqlalchemy.Float instead of values of them.
    • Distributions are saved as encoded JSON strings.
• set_study_user_attr / set_study_system_attr / set_trial_user_attr / set_trial_system_attr
  • It dumps all the values ​​into JSON strings and saves them.

GrpcStorageProxy

The precision of values are specified in api.proto.

• set_trial_state_values
  • Saved as double.
• set_trial_intermediate_value
  • Saved as double.
• set_trial_param
  • FloatDistribution
    • Saved as double.
  • CategoricalDistribution
    • Indexes are saved as doubles instead of values.
• set_study_user_attr / set_study_system_attr / set_trial_user_attr / set_trial_system_attr
  • Saved as JSON strings.