Fix warnings in HiveBucketing
Fix handling of Hive tables bucketed on string
Add 0.68 release notes
Fix Hive bucketing test
[maven-release-plugin] prepare release 0.68
[maven-release-plugin] prepare for next development iteration
Increase parallelism in unit tests to 4
Add timestamp with time zone minus interval year month operator
Support explaining sampled queries
Move drop table logic to NativeMetadata
Static import query execution factories
Used shared executor for query execution
Rename InMemoryMetadata to TestingMetadata
Remove useless check in NativeMetadata
Use checkType in NativeMetadata
Fix warnings in MetadataManager
Add machine learning functions plugin

Add functions to train and use machine learning models (classifiers and
regressors) in Presto. This is currently only a proof of concept, and is
not ready for use in production. Example usage is as follows:

SELECT evaluate_classifier_predictions(label, classify(features, model))
FROM (
    SELECT learn_classifier(label, features) AS model
    FROM my_training_data;
)
CROSS JOIN my_validation_data;
Add missing file
Fix MappedRecordCursor bug
Make TestDateTimeFunctions single threaded