spark.py

#
#   Copyright 2020 Logical Clocks AB
#
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#
#       http://www.apache.org/licenses/LICENSE-2.0
#
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.
#
from __future__ import annotations

import copy
import json
import os
import re
import shutil
import uuid
import warnings
from datetime import date, datetime, timezone
from typing import TYPE_CHECKING, Any, Dict, List, Optional, TypeVar, Union


if TYPE_CHECKING:
    import great_expectations
    from pyspark.rdd import RDD
    from pyspark.sql import DataFrame

import numpy as np
import pandas as pd
import tzlocal
from hsfs.constructor import query

# in case importing in %%local
from hsfs.core.vector_db_client import VectorDbClient


try:
    import pyspark
    from pyspark import SparkFiles
    from pyspark.rdd import RDD
    from pyspark.sql import DataFrame, SparkSession, SQLContext
    from pyspark.sql.avro.functions import from_avro, to_avro
    from pyspark.sql.functions import (
        array,
        col,
        concat,
        from_json,
        lit,
        struct,
        udf,
    )
    from pyspark.sql.types import (
        ArrayType,
        BinaryType,
        BooleanType,
        ByteType,
        DateType,
        DecimalType,
        DoubleType,
        FloatType,
        IntegerType,
        LongType,
        ShortType,
        StringType,
        StructField,
        StructType,
        TimestampType,
    )

    if pd.__version__ >= "2.0.0" and pyspark.__version__ < "3.2.3":

        def iteritems(self):
            return self.items()

        pd.DataFrame.iteritems = iteritems
except ImportError:
    pass

from hopsworks_common import client
from hopsworks_common.client.exceptions import FeatureStoreException
from hsfs import (
    feature,
    feature_view,
    training_dataset,
    training_dataset_feature,
    transformation_function,
    util,
)
from hsfs import feature_group as fg_mod
from hsfs.core import (
    dataset_api,
    delta_engine,
    hudi_engine,
    kafka_engine,
    transformation_function_engine,
)
from hsfs.core.constants import HAS_AVRO, HAS_GREAT_EXPECTATIONS
from hsfs.decorators import uses_great_expectations
from hsfs.storage_connector import StorageConnector
from hsfs.training_dataset_split import TrainingDatasetSplit


if HAS_GREAT_EXPECTATIONS:
    import great_expectations

if HAS_AVRO:
    import avro


class Engine:
    HIVE_FORMAT = "hive"
    KAFKA_FORMAT = "kafka"

    APPEND = "append"
    OVERWRITE = "overwrite"

    def __init__(self):
        self._spark_session = SparkSession.builder.enableHiveSupport().getOrCreate()
        self._spark_context = self._spark_session.sparkContext
        # self._spark_context.setLogLevel("DEBUG")
        self._jvm = self._spark_context._jvm

        self._spark_session.conf.set("hive.exec.dynamic.partition", "true")
        self._spark_session.conf.set("hive.exec.dynamic.partition.mode", "nonstrict")
        self._spark_session.conf.set("spark.sql.hive.convertMetastoreParquet", "false")
        self._spark_session.conf.set("spark.sql.session.timeZone", "UTC")
        self._dataset_api = dataset_api.DatasetApi()

    def sql(
        self,
        sql_query,
        feature_store,
        connector,
        dataframe_type,
        read_options,
        schema=None,
    ):
        if not connector:
            result_df = self._sql_offline(sql_query, feature_store)
        else:
            result_df = connector.read(sql_query, None, {}, None)

        self.set_job_group("", "")
        return self._return_dataframe_type(result_df, dataframe_type)

    def is_flyingduck_query_supported(self, query, read_options=None):
        return False  # we do not support flyingduck on pyspark clients

    def _sql_offline(self, sql_query, feature_store):
        # set feature store
        self._spark_session.sql("USE {}".format(feature_store))
        return self._spark_session.sql(sql_query)

    def show(self, sql_query, feature_store, n, online_conn, read_options=None):
        return self.sql(
            sql_query, feature_store, online_conn, "default", read_options
        ).show(n)

    def read_vector_db(
        self,
        feature_group: fg_mod.FeatureGroup,
        n: int = None,
        dataframe_type: str = "default",
    ) -> Union[
        pd.DataFrame, np.ndarray, List[List[Any]], TypeVar("pyspark.sql.DataFrame")
    ]:
        results = VectorDbClient.read_feature_group(feature_group, n)
        feature_names = [f.name for f in feature_group.features]
        dataframe_type = dataframe_type.lower()
        if dataframe_type in ["default", "spark"]:
            if len(results) == 0:
                return self._spark_session.createDataFrame(
                    self._spark_session.sparkContext.emptyRDD(), StructType()
                )
            else:
                return self._spark_session.createDataFrame(results, feature_names)
        else:
            df = pd.DataFrame(results, columns=feature_names, index=None)
            return self._return_dataframe_type(df, dataframe_type)

    def set_job_group(self, group_id, description):
        self._spark_session.sparkContext.setJobGroup(group_id, description)

    def register_external_temporary_table(self, external_fg, alias):
        if not isinstance(external_fg, fg_mod.SpineGroup):
            external_dataset = external_fg.storage_connector.read(
                external_fg.query,
                external_fg.data_format,
                external_fg.options,
                external_fg.prepare_spark_location(),
            )
        else:
            external_dataset = external_fg.dataframe

        external_dataset.createOrReplaceTempView(alias)
        return external_dataset

    def register_hudi_temporary_table(
        self, hudi_fg_alias, feature_store_id, feature_store_name, read_options
    ):
        hudi_engine_instance = hudi_engine.HudiEngine(
            feature_store_id,
            feature_store_name,
            hudi_fg_alias.feature_group,
            self._spark_context,
            self._spark_session,
        )

        hudi_engine_instance.register_temporary_table(
            hudi_fg_alias,
            read_options,
        )

        hudi_engine_instance.reconcile_hudi_schema(
            self.save_empty_dataframe, hudi_fg_alias, read_options
        )

    def register_delta_temporary_table(
        self, delta_fg_alias, feature_store_id, feature_store_name, read_options
    ):
        delta_engine_instance = delta_engine.DeltaEngine(
            feature_store_id,
            feature_store_name,
            delta_fg_alias.feature_group,
            self._spark_session,
            self._spark_context,
        )

        delta_engine_instance.register_temporary_table(
            delta_fg_alias,
            read_options,
        )

    def _return_dataframe_type(self, dataframe, dataframe_type):
        if dataframe_type.lower() in ["default", "spark"]:
            return dataframe

        # Converting to pandas dataframe if return type is not spark
        if isinstance(dataframe, DataFrame):
            dataframe = dataframe.toPandas()

        if dataframe_type.lower() == "pandas":
            return dataframe
        if dataframe_type.lower() == "numpy":
            return dataframe.values
        if dataframe_type.lower() == "python":
            return dataframe.values.tolist()

        raise TypeError(
            "Dataframe type `{}` not supported on this platform.".format(dataframe_type)
        )

    def convert_to_default_dataframe(self, dataframe):
        if isinstance(dataframe, list):
            dataframe = np.array(dataframe)

        if isinstance(dataframe, np.ndarray):
            if dataframe.ndim != 2:
                raise TypeError(
                    "Cannot convert numpy array that do not have two dimensions to a dataframe. "
                    "The number of dimensions are: {}".format(dataframe.ndim)
                )
            num_cols = dataframe.shape[1]
            dataframe_dict = {}
            for n_col in list(range(num_cols)):
                col_name = "col_" + str(n_col)
                dataframe_dict[col_name] = dataframe[:, n_col]
            dataframe = pd.DataFrame(dataframe_dict)

        if isinstance(dataframe, pd.DataFrame):
            # convert timestamps to current timezone
            local_tz = tzlocal.get_localzone()
            # make shallow copy so the original df does not get changed
            dataframe_copy = dataframe.copy(deep=False)
            for c in dataframe_copy.columns:
                if isinstance(
                    dataframe_copy[c].dtype, pd.core.dtypes.dtypes.DatetimeTZDtype
                ):
                    # convert to utc timestamp
                    dataframe_copy[c] = dataframe_copy[c].dt.tz_convert(None)
                if dataframe_copy[c].dtype == np.dtype("datetime64[ns]"):
                    # set the timezone to the client's timezone because that is
                    # what spark expects.
                    dataframe_copy[c] = dataframe_copy[c].dt.tz_localize(
                        str(local_tz), ambiguous="infer", nonexistent="shift_forward"
                    )
            dataframe = self._spark_session.createDataFrame(dataframe_copy)
        elif isinstance(dataframe, RDD):
            dataframe = dataframe.toDF()

        if isinstance(dataframe, DataFrame):
            upper_case_features = [
                c for c in dataframe.columns if any(re.finditer("[A-Z]", c))
            ]
            space_features = [c for c in dataframe.columns if " " in c]
            if len(upper_case_features) > 0:
                warnings.warn(
                    "The ingested dataframe contains upper case letters in feature names: `{}`. "
                    "Feature names are sanitized to lower case in the feature store.".format(
                        upper_case_features
                    ),
                    util.FeatureGroupWarning,
                    stacklevel=1,
                )
            if len(space_features) > 0:
                warnings.warn(
                    "The ingested dataframe contains feature names with spaces: `{}`. "
                    "Feature names are sanitized to use underscore '_' in the feature store.".format(
                        space_features
                    ),
                    util.FeatureGroupWarning,
                    stacklevel=1,
                )

            lowercase_dataframe = dataframe.select(
                [col(x).alias(util.autofix_feature_name(x)) for x in dataframe.columns]
            )
            # for streaming dataframes this will be handled in DeltaStreamerTransformer.java class
            if not lowercase_dataframe.isStreaming:
                nullable_schema = copy.deepcopy(lowercase_dataframe.schema)
                for struct_field in nullable_schema:
                    struct_field.nullable = True
                lowercase_dataframe = self._spark_session.createDataFrame(
                    lowercase_dataframe.rdd, nullable_schema
                )

            return lowercase_dataframe
        if dataframe == "spine":
            return None

        raise TypeError(
            "The provided dataframe type is not recognized. Supported types are: spark rdds, spark dataframes, "
            "pandas dataframes, python 2D lists, and numpy 2D arrays. The provided dataframe has type: {}".format(
                type(dataframe)
            )
        )

    def save_dataframe(
        self,
        feature_group,
        dataframe,
        operation,
        online_enabled,
        storage,
        offline_write_options,
        online_write_options,
        validation_id=None,
    ):
        try:
            # Currently on-demand transformation functions not supported in external feature groups.
            if (
                not isinstance(feature_group, fg_mod.ExternalFeatureGroup)
                and feature_group.transformation_functions
            ):
                dataframe = self._apply_transformation_function(
                    feature_group.transformation_functions, dataframe
                )
            if (
                isinstance(feature_group, fg_mod.ExternalFeatureGroup)
                and feature_group.online_enabled
            ) or feature_group.stream:
                self._save_online_dataframe(
                    feature_group, dataframe, online_write_options
                )
            else:
                if storage == "offline" or not online_enabled:
                    self._save_offline_dataframe(
                        feature_group,
                        dataframe,
                        operation,
                        offline_write_options,
                        validation_id,
                    )
                elif storage == "online":
                    self._save_online_dataframe(
                        feature_group, dataframe, online_write_options
                    )
                elif online_enabled and storage is None:
                    self._save_offline_dataframe(
                        feature_group,
                        dataframe,
                        operation,
                        offline_write_options,
                    )
                    self._save_online_dataframe(
                        feature_group, dataframe, online_write_options
                    )
        except Exception as e:
            raise FeatureStoreException(e).with_traceback(e.__traceback__) from e

    def save_stream_dataframe(
        self,
        feature_group: Union[fg_mod.FeatureGroup, fg_mod.ExternalFeatureGroup],
        dataframe,
        query_name,
        output_mode,
        await_termination: bool,
        timeout,
        checkpoint_dir: Optional[str],
        write_options: Optional[Dict[str, Any]],
    ):
        if feature_group.transformation_functions:
            dataframe = self._apply_transformation_function(
                feature_group.transformation_functions, dataframe
            )

        write_options = kafka_engine.get_kafka_config(
            feature_group.feature_store_id, write_options, engine="spark"
        )
        serialized_df = self._online_fg_to_avro(
            feature_group, self._encode_complex_features(feature_group, dataframe)
        )

        project_id = str(feature_group.feature_store.project_id)
        feature_group_id = str(feature_group._id)
        subject_id = str(feature_group.subject["id"]).encode("utf8")

        if query_name is None:
            query_name = (
                f"insert_stream_{project_id}_{feature_group_id}"
                f"_{feature_group.name}_{feature_group.version}_onlinefs"
            )

        query = (
            serialized_df.withColumn(
                "headers",
                array(
                    struct(
                        lit("projectId").alias("key"),
                        lit(project_id.encode("utf8")).alias("value"),
                    ),
                    struct(
                        lit("featureGroupId").alias("key"),
                        lit(feature_group_id.encode("utf8")).alias("value"),
                    ),
                    struct(
                        lit("subjectId").alias("key"), lit(subject_id).alias("value")
                    ),
                ),
            )
            .writeStream.outputMode(output_mode)
            .format(self.KAFKA_FORMAT)
            .option(
                "checkpointLocation",
                "/Projects/"
                + client.get_instance()._project_name
                + "/Resources/"
                + query_name
                + "-checkpoint"
                if checkpoint_dir is None
                else checkpoint_dir,
            )
            .options(**write_options)
            .option("topic", feature_group._online_topic_name)
            .queryName(query_name)
            .start()
        )

        if await_termination:
            query.awaitTermination(timeout)

        return query

    def _save_offline_dataframe(
        self,
        feature_group,
        dataframe,
        operation,
        write_options,
        validation_id=None,
    ):
        if feature_group.time_travel_format == "HUDI":
            hudi_engine_instance = hudi_engine.HudiEngine(
                feature_group.feature_store_id,
                feature_group.feature_store_name,
                feature_group,
                self._spark_session,
                self._spark_context,
            )

            hudi_engine_instance.save_hudi_fg(
                dataframe, self.APPEND, operation, write_options, validation_id
            )
        elif feature_group.time_travel_format == "DELTA":
            delta_engine_instance = delta_engine.DeltaEngine(
                feature_group.feature_store_id,
                feature_group.feature_store_name,
                feature_group,
                self._spark_session,
                self._spark_context,
            )
            delta_engine_instance.save_delta_fg(dataframe, write_options, validation_id)
        else:
            dataframe.write.format(self.HIVE_FORMAT).mode(self.APPEND).options(
                **write_options
            ).partitionBy(
                feature_group.partition_key if feature_group.partition_key else []
            ).saveAsTable(feature_group._get_table_name())

    def _save_online_dataframe(self, feature_group, dataframe, write_options):
        write_options = kafka_engine.get_kafka_config(
            feature_group.feature_store_id, write_options, engine="spark"
        )

        serialized_df = self._online_fg_to_avro(
            feature_group, self._encode_complex_features(feature_group, dataframe)
        )

        project_id = str(feature_group.feature_store.project_id).encode("utf8")
        feature_group_id = str(feature_group._id).encode("utf8")
        subject_id = str(feature_group.subject["id"]).encode("utf8")

        serialized_df.withColumn(
            "headers",
            array(
                struct(lit("projectId").alias("key"), lit(project_id).alias("value")),
                struct(
                    lit("featureGroupId").alias("key"),
                    lit(feature_group_id).alias("value"),
                ),
                struct(lit("subjectId").alias("key"), lit(subject_id).alias("value")),
            ),
        ).write.format(self.KAFKA_FORMAT).options(**write_options).option(
            "topic", feature_group._online_topic_name
        ).save()

    def _encode_complex_features(
        self,
        feature_group: Union[fg_mod.FeatureGroup, fg_mod.ExternalFeatureGroup],
        dataframe: Union[RDD, DataFrame],
    ):
        """Encodes all complex type features to binary using their avro type as schema."""
        return dataframe.select(
            [
                field["name"]
                if field["name"] not in feature_group.get_complex_features()
                else to_avro(
                    field["name"], feature_group._get_feature_avro_schema(field["name"])
                ).alias(field["name"])
                for field in json.loads(feature_group.avro_schema)["fields"]
            ]
        )

    def _online_fg_to_avro(
        self,
        feature_group: Union[fg_mod.FeatureGroup, fg_mod.ExternalFeatureGroup],
        dataframe: Union[DataFrame, RDD],
    ):
        """Packs all features into named struct to be serialized to single avro/binary
        column. And packs primary key into arry to be serialized for partitioning.
        """
        return dataframe.select(
            [
                # be aware: primary_key array should always be sorted
                to_avro(
                    concat(
                        *[
                            col(f).cast("string")
                            for f in sorted(feature_group.primary_key)
                        ]
                    )
                ).alias("key"),
                to_avro(
                    struct(
                        [
                            field["name"]
                            for field in json.loads(feature_group.avro_schema)["fields"]
                        ]
                    ),
                    feature_group._get_encoded_avro_schema(),
                ).alias("value"),
            ]
        )

    def get_training_data(
        self,
        training_dataset: training_dataset.TrainingDataset,
        feature_view_obj: feature_view.FeatureView,
        query_obj: query.Query,
        read_options: Dict[str, Any],
        dataframe_type: str,
        training_dataset_version: int = None,
    ):
        """
        Function that creates or retrieves already created the training dataset.

        # Arguments
            training_dataset_obj `TrainingDataset`: The training dataset metadata object.
            feature_view_obj `FeatureView`: The feature view object for the which the training data is being created.
            query_obj `Query`: The query object that contains the query used to create the feature view.
            read_options `Dict[str, Any]`: Dictionary that can be used to specify extra parameters for reading data.
            dataframe_type `str`: The type of dataframe returned.
            training_dataset_version `int`: Version of training data to be retrieved.
        # Raises
            `ValueError`: If the training dataset statistics could not be retrieved.
        """
        return self.write_training_dataset(
            training_dataset,
            query_obj,
            read_options,
            None,
            read_options=read_options,
            to_df=True,
            feature_view_obj=feature_view_obj,
            training_dataset_version=training_dataset_version,
        )

    def split_labels(self, df, labels, dataframe_type):
        if labels:
            if isinstance(df, pd.DataFrame):
                labels_df = df[labels]
                df_new = df.drop(columns=labels)
            else:
                labels_df = df.select(*labels)
                df_new = df.drop(*labels)
            return (
                self._return_dataframe_type(df_new, dataframe_type),
                self._return_dataframe_type(labels_df, dataframe_type),
            )
        else:
            return self._return_dataframe_type(df, dataframe_type), None

    def drop_columns(self, df, drop_cols):
        return df.drop(*drop_cols)

    def write_training_dataset(
        self,
        training_dataset: training_dataset.TrainingDataset,
        query_obj: query.Query,
        user_write_options: Dict[str, Any],
        save_mode: str,
        read_options: Dict[str, Any] = None,
        feature_view_obj: feature_view.FeatureView = None,
        to_df: bool = False,
        training_dataset_version: Optional[int] = None,
    ):
        """
        Function that creates or retrieves already created the training dataset.

        # Arguments
            training_dataset `TrainingDataset`: The training dataset metadata object.
            query_obj `Query`: The query object that contains the query used to create the feature view.
            user_write_options `Dict[str, Any]`: Dictionary that can be used to specify extra parameters for writing data using spark.
            save_mode `str`: Spark save mode to be used while writing data.
            read_options `Dict[str, Any]`: Dictionary that can be used to specify extra parameters for reading data.
            feature_view_obj `FeatureView`: The feature view object for the which the training data is being created.
            to_df `bool`: Return dataframe instead of writing the data.
            training_dataset_version `Optional[int]`: Version of training data to be retrieved.
        # Raises
            `ValueError`: If the training dataset statistics could not be retrieved.
        """
        write_options = self.write_options(
            training_dataset.data_format, user_write_options
        )
        if read_options is None:
            read_options = {}

        if len(training_dataset.splits) == 0:
            if isinstance(query_obj, query.Query):
                dataset = self.convert_to_default_dataframe(
                    query_obj.read(read_options=read_options)
                )
            else:
                raise ValueError("Dataset should be a query.")

            # if training_dataset_version is None:
            transformation_function_engine.TransformationFunctionEngine.compute_and_set_feature_statistics(
                training_dataset, feature_view_obj, dataset
            )
            # else:
            #    transformation_function_engine.TransformationFunctionEngine.get_and_set_feature_statistics(
            #        training_dataset, feature_view_obj, training_dataset_version
            #    )

            if training_dataset.coalesce:
                dataset = dataset.coalesce(1)
            path = training_dataset.location + "/" + training_dataset.name
            return self._write_training_dataset_single(
                feature_view_obj.transformation_functions,
                dataset,
                training_dataset.storage_connector,
                training_dataset.data_format,
                write_options,
                save_mode,
                path,
                to_df=to_df,
            )
        else:
            split_dataset = self._split_df(
                query_obj, training_dataset, read_options=read_options
            )
            for key in split_dataset:
                if training_dataset.coalesce:
                    split_dataset[key] = split_dataset[key].coalesce(1)

                split_dataset[key] = split_dataset[key].cache()

            if training_dataset_version is None:
                transformation_function_engine.TransformationFunctionEngine.compute_and_set_feature_statistics(
                    training_dataset, feature_view_obj, split_dataset
                )
            else:
                transformation_function_engine.TransformationFunctionEngine.get_and_set_feature_statistics(
                    training_dataset, feature_view_obj, training_dataset_version
                )

            return self._write_training_dataset_splits(
                training_dataset,
                split_dataset,
                write_options,
                save_mode,
                to_df=to_df,
                transformation_functions=feature_view_obj.transformation_functions,
            )

    def _split_df(self, query_obj, training_dataset, read_options=None):
        if read_options is None:
            read_options = {}
        if (
            training_dataset.splits[0].split_type
            == TrainingDatasetSplit.TIME_SERIES_SPLIT
        ):
            event_time = query_obj._left_feature_group.event_time
            if event_time not in [_feature.name for _feature in query_obj.features]:
                query_obj.append_feature(
                    query_obj._left_feature_group.__getattr__(event_time)
                )
                return self._time_series_split(
                    training_dataset,
                    query_obj.read(read_options=read_options),
                    event_time,
                    drop_event_time=True,
                )
            else:
                return self._time_series_split(
                    training_dataset,
                    query_obj.read(read_options=read_options),
                    event_time,
                )
        else:
            return self._random_split(
                query_obj.read(read_options=read_options), training_dataset
            )

    def _random_split(self, dataset, training_dataset):
        splits = [(split.name, split.percentage) for split in training_dataset.splits]
        split_weights = [split[1] for split in splits]
        split_dataset = dataset.randomSplit(split_weights, training_dataset.seed)
        return dict([(split[0], split_dataset[i]) for i, split in enumerate(splits)])

    def _time_series_split(
        self, training_dataset, dataset, event_time, drop_event_time=False
    ):
        # duplicate the code from util module to avoid udf errors on windows
        def check_timestamp_format_from_date_string(input_date):
            date_format_patterns = {
                r"^([0-9]{4})([0-9]{2})([0-9]{2})$": "%Y%m%d",
                r"^([0-9]{4})([0-9]{2})([0-9]{2})([0-9]{2})$": "%Y%m%d%H",
                r"^([0-9]{4})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})$": "%Y%m%d%H%M",
                r"^([0-9]{4})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})$": "%Y%m%d%H%M%S",
                r"^([0-9]{4})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{3})$": "%Y%m%d%H%M%S%f",
                r"^([0-9]{4})([0-9]{2})([0-9]{2})T([0-9]{2})([0-9]{2})([0-9]{2})([0-9]{6})Z$": "ISO",
            }
            normalized_date = (
                input_date.replace("/", "")
                .replace("-", "")
                .replace(" ", "")
                .replace(":", "")
                .replace(".", "")
            )

            date_format = None
            for pattern in date_format_patterns:
                date_format_pattern = re.match(pattern, normalized_date)
                if date_format_pattern:
                    date_format = date_format_patterns[pattern]
                    break

            if date_format is None:
                raise ValueError(
                    "Unable to identify format of the provided date value : "
                    + input_date
                )

            return normalized_date, date_format

        def get_timestamp_from_date_string(input_date):
            norm_input_date, date_format = check_timestamp_format_from_date_string(
                input_date
            )
            try:
                if date_format != "ISO":
                    date_time = datetime.strptime(norm_input_date, date_format)
                else:
                    date_time = datetime.fromisoformat(input_date[:-1])
            except ValueError as err:
                raise ValueError(
                    "Unable to parse the normalized input date value : "
                    + norm_input_date
                    + " with format "
                    + date_format
                ) from err
            if date_time.tzinfo is None:
                date_time = date_time.replace(tzinfo=timezone.utc)
            return int(float(date_time.timestamp()) * 1000)

        def convert_event_time_to_timestamp(event_time):
            if not event_time:
                return None
            if isinstance(event_time, str):
                return get_timestamp_from_date_string(event_time)
            elif isinstance(event_time, pd._libs.tslibs.timestamps.Timestamp):
                # convert to unix epoch time in milliseconds.
                event_time = event_time.to_pydatetime()
                # convert to unix epoch time in milliseconds.
                if event_time.tzinfo is None:
                    event_time = event_time.replace(tzinfo=timezone.utc)
                return int(event_time.timestamp() * 1000)
            elif isinstance(event_time, datetime):
                # convert to unix epoch time in milliseconds.
                if event_time.tzinfo is None:
                    event_time = event_time.replace(tzinfo=timezone.utc)
                return int(event_time.timestamp() * 1000)
            elif isinstance(event_time, date):
                # convert to unix epoch time in milliseconds.
                event_time = datetime(*event_time.timetuple()[:7])
                if event_time.tzinfo is None:
                    event_time = event_time.replace(tzinfo=timezone.utc)
                return int(event_time.timestamp() * 1000)
            elif isinstance(event_time, int):
                if event_time == 0:
                    raise ValueError("Event time should be greater than 0.")
                # jdbc supports timestamp precision up to second only.
                if len(str(event_time)) <= 10:
                    event_time = event_time * 1000
                return event_time
            else:
                raise ValueError(
                    "Given event time should be in `datetime`, `date`, `str` or `int` type"
                )

        # registering the UDF
        _convert_event_time_to_timestamp = udf(
            convert_event_time_to_timestamp, LongType()
        )

        result_dfs = {}
        ts_col = _convert_event_time_to_timestamp(col(event_time))
        for split in training_dataset.splits:
            result_df = dataset.filter(ts_col >= split.start_time).filter(
                ts_col < split.end_time
            )
            if drop_event_time:
                result_df = result_df.drop(event_time)
            result_dfs[split.name] = result_df
        return result_dfs

    def _write_training_dataset_splits(
        self,
        training_dataset,
        feature_dataframes,
        write_options,
        save_mode,
        to_df=False,
        transformation_functions: List[
            transformation_function.TransformationFunction
        ] = None,
    ):
        for split_name, feature_dataframe in feature_dataframes.items():
            split_path = training_dataset.location + "/" + str(split_name)
            feature_dataframes[split_name] = self._write_training_dataset_single(
                transformation_functions,
                feature_dataframe,
                training_dataset.storage_connector,
                training_dataset.data_format,
                write_options,
                save_mode,
                split_path,
                to_df=to_df,
            )

        if to_df:
            return feature_dataframes

    def _write_training_dataset_single(
        self,
        transformation_functions,
        feature_dataframe,
        storage_connector,
        data_format,
        write_options,
        save_mode,
        path,
        to_df=False,
    ):
        # apply transformation functions (they are applied separately to each split)
        feature_dataframe = self._apply_transformation_function(
            transformation_functions, dataset=feature_dataframe
        )
        if to_df:
            return feature_dataframe
        # TODO: currently not supported petastorm, hdf5 and npy file formats
        if data_format.lower() == "tsv":
            data_format = "csv"

        path = self.setup_storage_connector(storage_connector, path)

        feature_dataframe.write.format(data_format).options(**write_options).mode(
            save_mode
        ).save(path)

        feature_dataframe.unpersist()

    def read(
        self, storage_connector, data_format, read_options, location, dataframe_type
    ):
        if not data_format:
            raise FeatureStoreException("data_format is not specified")

        if isinstance(location, str):
            if data_format.lower() in ["delta", "parquet", "hudi", "orc", "bigquery"]:
                # All the above data format readers can handle partitioning
                # by their own, they don't need /**
                # for bigquery, argument location can be a SQL query
                path = location
            else:
                path = location + "/**"

            if data_format.lower() == "tsv":
                data_format = "csv"

        else:
            path = None

        path = self.setup_storage_connector(storage_connector, path)

        return self._return_dataframe_type(
            self._spark_session.read.format(data_format)
            .options(**(read_options if read_options else {}))
            .load(path),
            dataframe_type=dataframe_type,
        )

    def read_stream(
        self,
        storage_connector,
        message_format,
        schema,
        options,
        include_metadata,
    ):
        # ideally all this logic should be in the storage connector in case we add more
        # streaming storage connectors...
        stream = self._spark_session.readStream.format(
            storage_connector.SPARK_FORMAT
        )  # todo SPARK_FORMAT available only for KAFKA connectors

        # set user options last so that they overwrite any default options
        stream = stream.options(**storage_connector.spark_options(), **options)

        if storage_connector.type == StorageConnector.KAFKA:
            return self._read_stream_kafka(
                stream, message_format, schema, include_metadata
            )

    def _read_stream_kafka(self, stream, message_format, schema, include_metadata):
        kafka_cols = [
            col("key"),
            col("topic"),
            col("partition"),
            col("offset"),
            col("timestamp"),
            col("timestampType"),
        ]

        if message_format == "avro" and schema is not None:
            # check if vallid avro schema
            avro.schema.parse(schema)
            df = stream.load()
            if include_metadata is True:
                return df.select(
                    *kafka_cols, from_avro(df.value, schema).alias("value")
                ).select(*kafka_cols, col("value.*"))
            return df.select(from_avro(df.value, schema).alias("value")).select(
                col("value.*")
            )
        elif message_format == "json" and schema is not None:
            df = stream.load()
            if include_metadata is True:
                return df.select(
                    *kafka_cols,
                    from_json(df.value.cast("string"), schema).alias("value"),
                ).select(*kafka_cols, col("value.*"))
            return df.select(
                from_json(df.value.cast("string"), schema).alias("value")
            ).select(col("value.*"))

        if include_metadata is True:
            return stream.load()
        return stream.load().select("key", "value")

    def add_file(self, file):
        if not file:
            return file

        # This is used for unit testing
        if not file.startswith("file://"):
            file = "hdfs://" + file

        file_name = os.path.basename(file)

        # for external clients, download the file
        if client._is_external():
            tmp_file = os.path.join(SparkFiles.getRootDirectory(), file_name)
            print("Reading key file from storage connector.")
            response = self._dataset_api.read_content(file, util.get_dataset_type(file))

            with open(tmp_file, "wb") as f:
                f.write(response.content)
        else:
            self._spark_context.addFile(file)

            # The file is not added to the driver current working directory
            # We should add it manually by copying from the download location
            # The file will be added to the executors current working directory
            # before the next task is executed
            shutil.copy(SparkFiles.get(file_name), file_name)

        return file_name

    def profile(
        self,
        dataframe,
        relevant_columns,
        correlations,
        histograms,
        exact_uniqueness=True,
    ):
        """Profile a dataframe with Deequ."""
        return self._jvm.com.logicalclocks.hsfs.spark.engine.SparkEngine.getInstance().profile(
            dataframe._jdf,
            relevant_columns,
            correlations,
            histograms,
            exact_uniqueness,
        )

    @uses_great_expectations
    def validate_with_great_expectations(
        self,
        dataframe: DataFrame,  # noqa: F821
        expectation_suite: great_expectations.core.ExpectationSuite,  # noqa: F821
        ge_validate_kwargs: Optional[dict],
    ):
        # NOTE: InMemoryStoreBackendDefaults SHOULD NOT BE USED in normal settings. You
        # may experience data loss as it persists nothing. It is used here for testing.
        # Please refer to docs to learn how to instantiate your DataContext.
        store_backend_defaults = (
            great_expectations.data_context.types.base.InMemoryStoreBackendDefaults()
        )
        data_context_config = (
            great_expectations.data_context.types.base.DataContextConfig(
                store_backend_defaults=store_backend_defaults,
                checkpoint_store_name=store_backend_defaults.checkpoint_store_name,
            )
        )
        context = great_expectations.data_context.BaseDataContext(
            project_config=data_context_config
        )

        datasource = {
            "name": "my_spark_dataframe",
            "class_name": "Datasource",
            "execution_engine": {
                "class_name": "SparkDFExecutionEngine",
                "force_reuse_spark_context": True,
            },
            "data_connectors": {
                "default_runtime_data_connector_name": {
                    "class_name": "RuntimeDataConnector",
                    "batch_identifiers": ["batch_id"],
                }
            },
        }
        context.add_datasource(**datasource)

        # Here is a RuntimeBatchRequest using a dataframe
        batch_request = great_expectations.core.batch.RuntimeBatchRequest(
            datasource_name="my_spark_dataframe",
            data_connector_name="default_runtime_data_connector_name",
            data_asset_name="<YOUR_MEANGINGFUL_NAME>",  # This can be anything that identifies this data_asset for you
            batch_identifiers={"batch_id": "default_identifier"},
            runtime_parameters={"batch_data": dataframe},  # Your dataframe goes here
        )
        context.save_expectation_suite(expectation_suite)
        validator = context.get_validator(
            batch_request=batch_request,
            expectation_suite_name=expectation_suite.expectation_suite_name,
        )
        report = validator.validate(**ge_validate_kwargs)

        return report

    def write_options(self, data_format, provided_options):
        if data_format.lower() == "tfrecords":
            options = dict(recordType="Example")
            options.update(provided_options)
        elif data_format.lower() == "tfrecord":
            options = dict(recordType="Example")
            options.update(provided_options)
        elif data_format.lower() == "csv":
            options = dict(delimiter=",", header="true")
            options.update(provided_options)
        elif data_format.lower() == "tsv":
            options = dict(delimiter="\t", header="true")
            options.update(provided_options)
        else:
            options = {}
            options.update(provided_options)
        return options

    def read_options(self, data_format, provided_options):
        if provided_options is None:
            provided_options = {}
        if data_format.lower() == "tfrecords":
            options = dict(recordType="Example", **provided_options)
            options.update(provided_options)
        elif data_format.lower() == "tfrecord":
            options = dict(recordType="Example")
            options.update(provided_options)
        elif data_format.lower() == "csv":
            options = dict(delimiter=",", header="true", inferSchema="true")
            options.update(provided_options)
        elif data_format.lower() == "tsv":
            options = dict(delimiter="\t", header="true", inferSchema="true")
            options.update(provided_options)
        else:
            options = {}
            options.update(provided_options)
        return options

    def parse_schema_feature_group(
        self,
        dataframe,
        time_travel_format=None,
        **kwargs,
    ):
        features = []

        using_hudi = time_travel_format == "HUDI"
        for feat in dataframe.schema:
            name = util.autofix_feature_name(feat.name)
            try:
                converted_type = Engine._convert_spark_type_to_offline_type(
                    feat.dataType, using_hudi
                )
            except ValueError as e:
                raise FeatureStoreException(f"Feature '{feat.name}': {str(e)}") from e
            features.append(
                feature.Feature(
                    name, converted_type, feat.metadata.get("description", None)
                )
            )
        return features

    def parse_schema_training_dataset(self, dataframe):
        return [
            training_dataset_feature.TrainingDatasetFeature(
                util.autofix_feature_name(feat.name), feat.dataType.simpleString()
            )
            for feat in dataframe.schema
        ]

    def setup_storage_connector(self, storage_connector, path=None):
        if storage_connector.type == StorageConnector.S3:
            return self._setup_s3_hadoop_conf(storage_connector, path)
        elif storage_connector.type == StorageConnector.ADLS:
            return self._setup_adls_hadoop_conf(storage_connector, path)
        elif storage_connector.type == StorageConnector.GCS:
            return self._setup_gcp_hadoop_conf(storage_connector, path)
        else:
            return path

    def _setup_s3_hadoop_conf(self, storage_connector, path):
        # For legacy behaviour set the S3 values at global level
        self._set_s3_hadoop_conf(storage_connector, "fs.s3a")

        # Set credentials at bucket level as well to allow users to use multiple
        # storage connector in the same application.
        self._set_s3_hadoop_conf(
            storage_connector, f"fs.s3a.bucket.{storage_connector.bucket}"
        )
        return path.replace("s3://", "s3a://", 1) if path is not None else None

    def _set_s3_hadoop_conf(self, storage_connector, prefix):
        if storage_connector.access_key:
            self._spark_context._jsc.hadoopConfiguration().set(
                f"{prefix}.access.key", storage_connector.access_key
            )
        if storage_connector.secret_key:
            self._spark_context._jsc.hadoopConfiguration().set(
                f"{prefix}.secret.key", storage_connector.secret_key
            )
        if storage_connector.server_encryption_algorithm:
            self._spark_context._jsc.hadoopConfiguration().set(
                f"{prefix}.server-side-encryption-algorithm",
                storage_connector.server_encryption_algorithm,
            )
        if storage_connector.server_encryption_key:
            self._spark_context._jsc.hadoopConfiguration().set(
                f"{prefix}.server-side-encryption-key",
                storage_connector.server_encryption_key,
            )
        if storage_connector.session_token:
            print(f"session token set for {prefix}")
            self._spark_context._jsc.hadoopConfiguration().set(
                f"{prefix}.aws.credentials.provider",
                "org.apache.hadoop.fs.s3a.TemporaryAWSCredentialsProvider",
            )
            self._spark_context._jsc.hadoopConfiguration().set(
                f"{prefix}.session.token",
                storage_connector.session_token,
            )

        # This is the name of the property as expected from the user, without the bucket name.
        FS_S3_ENDPOINT = "fs.s3a.endpoint"
        if FS_S3_ENDPOINT in storage_connector.arguments:
            self._spark_context._jsc.hadoopConfiguration().set(
                f"{prefix}.endpoint",
                storage_connector.spark_options().get(FS_S3_ENDPOINT),
            )

    def _setup_adls_hadoop_conf(self, storage_connector, path):
        for k, v in storage_connector.spark_options().items():
            self._spark_context._jsc.hadoopConfiguration().set(k, v)

        return path

    def is_spark_dataframe(self, dataframe):
        if isinstance(dataframe, DataFrame):
            return True
        return False

    def save_empty_dataframe(self, feature_group, new_features=None):
        location = feature_group.prepare_spark_location()

        dataframe = self._spark_session.read.format("hudi").load(location)

        if (new_features is not None):
            if isinstance(new_features, list):
                for new_feature in new_features:
                    dataframe = dataframe.withColumn(new_feature.name, lit(None).cast(new_feature.type))
            else:
                dataframe = dataframe.withColumn(new_features.name, lit(None).cast(new_features.type))


        self.save_dataframe(
            feature_group,
            dataframe.limit(0),
            "upsert",
            feature_group.online_enabled,
            "offline",
            {},
            {},
        )

    def add_cols_to_delta_table(self, feature_group, new_features):
        location = feature_group.prepare_spark_location()

        dataframe = self._spark_session.read.format("delta").load(location)

        if (new_features is not None):
            if isinstance(new_features, list):
                for new_feature in new_features:
                    dataframe = dataframe.withColumn(new_feature.name, lit("").cast(new_feature.type))
            else:
                dataframe = dataframe.withColumn(new_features.name, lit("").cast(new_features.type))

        dataframe.limit(0).write.format("delta").mode(
            "append"
        ).option("mergeSchema", "true").option(
            "spark.databricks.delta.schema.autoMerge.enabled", "true"
        ).save(location)

    def _apply_transformation_function(
        self,
        transformation_functions: List[transformation_function.TransformationFunction],
        dataset: DataFrame,
    ):
        """
        Apply transformation function to the dataframe.

        # Arguments
            transformation_functions `List[TransformationFunction]` : List of transformation functions.
            dataset `Union[DataFrame]`: A spark dataframe.
        # Returns
            `DataFrame`: A spark dataframe with the transformed data.
        # Raises
            `FeatureStoreException`: If any of the features mentioned in the transformation function is not present in the Feature View.
        """
        dropped_features = set()
        transformations = []
        transformation_features = []
        output_col_names = []
        explode_name = []
        for tf in transformation_functions:
            hopsworks_udf = tf.hopsworks_udf
            missing_features = set(hopsworks_udf.transformation_features) - set(
                dataset.columns
            )

            if missing_features:
                raise FeatureStoreException(
                    f"Features {missing_features} specified in the transformation function '{hopsworks_udf.function_name}' are not present in the feature view. Please specify the feature required correctly."
                )
            if tf.hopsworks_udf.dropped_features:
                dropped_features.update(tf.hopsworks_udf.dropped_features)

            pandas_udf = hopsworks_udf.get_udf()
            output_col_name = hopsworks_udf.output_column_names[0]

            transformations.append(pandas_udf)
            output_col_names.append(output_col_name)
            transformation_features.append(hopsworks_udf.transformation_features)

            if len(hopsworks_udf.return_types) > 1:
                explode_name.append(f"{output_col_name}.*")
            else:
                explode_name.append(output_col_name)

        untransformed_columns = []  # Untransformed column maintained as a list since order is imported while selecting features.
        for column in dataset.columns:
            if column not in dropped_features:
                untransformed_columns.append(column)
        # Applying transformations
        transformed_dataset = dataset.select(
            *untransformed_columns,
            *[
                fun(*feature).alias(output_col_name)
                for fun, feature, output_col_name in zip(
                    transformations, transformation_features, output_col_names
                )
            ],
        ).select(*untransformed_columns, *explode_name)

        return transformed_dataset

    def _setup_gcp_hadoop_conf(self, storage_connector, path):
        PROPERTY_ENCRYPTION_KEY = "fs.gs.encryption.key"
        PROPERTY_ENCRYPTION_HASH = "fs.gs.encryption.key.hash"
        PROPERTY_ALGORITHM = "fs.gs.encryption.algorithm"
        PROPERTY_GCS_FS_KEY = "fs.AbstractFileSystem.gs.impl"
        PROPERTY_GCS_FS_VALUE = "com.google.cloud.hadoop.fs.gcs.GoogleHadoopFS"
        PROPERTY_GCS_ACCOUNT_ENABLE = "google.cloud.auth.service.account.enable"
        PROPERTY_ACCT_EMAIL = "fs.gs.auth.service.account.email"
        PROPERTY_ACCT_KEY_ID = "fs.gs.auth.service.account.private.key.id"
        PROPERTY_ACCT_KEY = "fs.gs.auth.service.account.private.key"
        # The AbstractFileSystem for 'gs:' URIs
        self._spark_context._jsc.hadoopConfiguration().setIfUnset(
            PROPERTY_GCS_FS_KEY, PROPERTY_GCS_FS_VALUE
        )
        # Whether to use a service account for GCS authorization. Setting this
        # property to `false` will disable use of service accounts for authentication.
        self._spark_context._jsc.hadoopConfiguration().setIfUnset(
            PROPERTY_GCS_ACCOUNT_ENABLE, "true"
        )

        # The JSON key file of the service account used for GCS
        # access when google.cloud.auth.service.account.enable is true.
        local_path = self.add_file(storage_connector.key_path)
        with open(local_path, "r") as f_in:
            jsondata = json.load(f_in)
        self._spark_context._jsc.hadoopConfiguration().set(
            PROPERTY_ACCT_EMAIL, jsondata["client_email"]
        )
        self._spark_context._jsc.hadoopConfiguration().set(
            PROPERTY_ACCT_KEY_ID, jsondata["private_key_id"]
        )
        self._spark_context._jsc.hadoopConfiguration().set(
            PROPERTY_ACCT_KEY, jsondata["private_key"]
        )

        if storage_connector.algorithm:
            # if encryption fields present
            self._spark_context._jsc.hadoopConfiguration().set(
                PROPERTY_ALGORITHM, storage_connector.algorithm
            )
            self._spark_context._jsc.hadoopConfiguration().set(
                PROPERTY_ENCRYPTION_KEY, storage_connector.encryption_key
            )
            self._spark_context._jsc.hadoopConfiguration().set(
                PROPERTY_ENCRYPTION_HASH, storage_connector.encryption_key_hash
            )
        else:
            # unset if already set
            self._spark_context._jsc.hadoopConfiguration().unset(PROPERTY_ALGORITHM)
            self._spark_context._jsc.hadoopConfiguration().unset(
                PROPERTY_ENCRYPTION_HASH
            )
            self._spark_context._jsc.hadoopConfiguration().unset(
                PROPERTY_ENCRYPTION_KEY
            )

        return path

    def create_empty_df(self, streaming_df):
        return SQLContext(self._spark_context).createDataFrame(
            self._spark_context.emptyRDD(), streaming_df.schema
        )

    @staticmethod
    def get_unique_values(feature_dataframe, feature_name):
        unique_values = feature_dataframe.select(feature_name).distinct().collect()
        return [field[feature_name] for field in unique_values]

    @staticmethod
    def _convert_spark_type_to_offline_type(spark_type, using_hudi):
        # The HiveSyncTool is strict and does not support schema evolution from tinyint/short to
        # int. Avro, on the other hand, does not support tinyint/short and delivers them as int
        # to Hive. Therefore, we need to force Hive to create int-typed columns in the first place.

        if not using_hudi:
            return spark_type.simpleString()
        elif type(spark_type) is ByteType:
            return "int"
        elif type(spark_type) is ShortType:
            return "int"
        elif type(spark_type) in [
            BooleanType,
            IntegerType,
            LongType,
            FloatType,
            DoubleType,
            DecimalType,
            TimestampType,
            DateType,
            StringType,
            ArrayType,
            StructType,
            BinaryType,
        ]:
            return spark_type.simpleString()

        raise ValueError(f"spark type {str(type(spark_type))} not supported")

    @staticmethod
    def _convert_offline_type_to_spark_type(offline_type):
        if "array<" == offline_type[:6]:
            return ArrayType(
                Engine._convert_offline_type_to_spark_type(offline_type[6:-1])
            )
        elif "struct<label:string,index:int>" in offline_type:
            return StructType(
                [
                    StructField("label", StringType(), True),
                    StructField("index", IntegerType(), True),
                ]
            )
        elif offline_type.startswith("decimal"):
            return DecimalType()
        else:
            offline_type_spark_type_mapping = {
                "string": StringType(),
                "bigint": LongType(),
                "int": IntegerType(),
                "smallint": ShortType(),
                "tinyint": ByteType(),
                "float": FloatType(),
                "double": DoubleType(),
                "timestamp": TimestampType(),
                "boolean": BooleanType(),
                "date": DateType(),
                "binary": BinaryType(),
            }
            if offline_type in offline_type_spark_type_mapping:
                return offline_type_spark_type_mapping[offline_type]
            else:
                raise FeatureStoreException(
                    f"Offline type {offline_type} cannot be converted to a spark type."
                )

    @staticmethod
    def cast_columns(df, schema, online=False):
        pyspark_schema = dict(
            [
                (_feat.name, Engine._convert_offline_type_to_spark_type(_feat.type))
                for _feat in schema
            ]
        )
        for _feat in pyspark_schema:
            df = df.withColumn(_feat, col(_feat).cast(pyspark_schema[_feat]))
        return df

    @staticmethod
    def is_connector_type_supported(type):
        return True

    def get_feature_logging_df(
        self,
        features: Union[
            pd.DataFrame, list[list], np.ndarray, TypeVar("pyspark.sql.DataFrame")
        ],
        fg: fg_mod.FeatureGroup = None,
        td_features: List[str] = None,
        td_predictions: List[training_dataset_feature.TrainingDatasetFeature] = None,
        td_col_name: Optional[str] = None,
        time_col_name: Optional[str] = None,
        model_col_name: Optional[str] = None,
        predictions: Optional[Union[pd.DataFrame, list[list], np.ndarray]] = None,
        training_dataset_version: Optional[int] = None,
        hsml_model: str = None,
        **kwargs,
    ):
        # do not take prediction separately because spark ml framework usually return feature together with the prediction
        # and it is costly to join them back
        df = self.convert_to_default_dataframe(features)
        if td_predictions:
            for f in td_predictions:
                if f.name not in df.columns:
                    df = df.withColumn(
                        f.name,
                        lit(None).cast(
                            Engine._convert_offline_type_to_spark_type(f.type)
                        ),
                    )

        uuid_udf = udf(lambda: str(uuid.uuid4()), StringType())

        # Add new columns to the DataFrame
        df = df.withColumn(td_col_name, lit(training_dataset_version).cast(LongType()))
        df = df.withColumn(model_col_name, lit(hsml_model).cast(StringType()))
        now = datetime.now()
        df = df.withColumn(time_col_name, lit(now).cast(TimestampType()))
        df = df.withColumn("log_id", uuid_udf())

        # Select the required columns
        return df.select(*[feat.name for feat in fg.features])

    @staticmethod
    def read_feature_log(query, time_col):
        df = query.read()
        return df.drop("log_id", time_col)


class SchemaError(Exception):
    """Thrown when schemas don't match"""