Standard Transformer

Standard Transformer is a built-in pre and post-processing steps supported by Merlin. With standard transformer, it’s possible to enrich the model’s incoming request with features from feast and transform the payload so that it’s compatible with API interface provided by the model. Same transformation can also be applied against the model’s response payload in the post-processing step, which allow users to adapt the response payload to make it suitable for consumption. Standard transformer supports http_json and upi_v1 protocol. For http_json protocol the standard transformer server runs rest server on top of http 1.1, upi_v1 protocol the server run grpc server.

Concept

Within standard transformer there are 2 process that user can specify: preprocess and postprocess.

Preprocess is useful to perform transformation against model’s incoming request such as enriching the request with features from Feast and transforming the client’s request to a format accepted by model service.

Post Processing is useful for performing transformation against model response so that it is more suitable for client consumption.

Within both preprocess and postprocess, there are 3 stages that users can specify:

• Input stage In the input stage, users specify all the data dependencies that are going to be used in subsequent stages. There are 2 operations available in these stages: variable declaration and table creation.

• Transformation stage. In this stage, the standard transformers perform transformation to the tables created in the input stage so that its structure is suitable for the output. In the transformation stage, users operate mainly on tables and are provided with 2 transformation types: single table transformation and table join.

• Output stage At this stage, both the preprocessing and postprocessing pipeline should create output payload which later on can be used as request payload for model predictor or the final response to be returned to downstream service/client. There are 3 types of output operation:

  • JSON Output. JSON output operation will return JSON output, this operation only applicable for http_json protocol

  • UPIPreprocessOutput. UPIPreprocessOutput will return UPI Request interface payload in a protobuf.Message type

  • UPIPostprocessOutput. UPIPostprocessOutput will return UPI Response interface payload in a protobuf.Message type

Jsonpath

Jsonpath is a way to find value from JSON payload. Standard transformer using jsonpath to find values either from request or model response payload. Standard transformer using Jsonpath in several operations:

• Variable declaration

• Feast entity value

• Base table

• Column value in table

• Json Output

Most of the jsonpath configuration is like this

fromJson:

    jsonPath:       # Json path in the incoming request / model response payload

    defaultValue:   # (Optional) Default value if value for the jsonPath is nil or empty 

    valueType:      # Type of default value, mandatory to specify if default value is exist

but in some part of operation like variable operation and feast entity extraction, jsonPath configuration is like below

    jsonPathConfig:

        jsonPath:       # Json path in the incoming request / model response payload

        defaultValue:   # (Optional) Default value if value for the jsonPath is nil or empty 

        valueType:      # Type of default value, mandatory to specify if default value is exist

Default Value

In standard transformer, user can specify jsonpath with default value if the result of jsonpath is empty or nil. Cases when default value is used:

• Result of jsonpath is nil

• Result of jsonpath is empty array

• Result of jsonpath is array, where some of its value is null

Value Type

Value Type	Syntax
Integer	INT
Float	FLOAT
Boolean	BOOL
String	STRING

For example, if we have incoming request

{
  "signature_name" : "predict",
  "instances": [
	{"sepal_length":2.8, "sepal_width":1.0, "petal_length":6.8, "petal_width":0.4},
	{"sepal_length":0.1, "sepal_width":0.5, "petal_length":1.8, "petal_width":2.4}
  ],
  "instances_with_null": [
	{"sepal_length":2.8, "sepal_width":1.0, "petal_length":6.8, "petal_width":0.4},
	{"sepal_length":0.1, "sepal_width":0.5, "petal_length":1.8, "petal_width":null},
          {"sepal_length":0.1, "sepal_width":0.5, "petal_length":1.8, "petal_width":0.5}
  ],
  "empty_array": [],
  "null_key": null,
  "array_object": [
	  {"exist_key":1},
	  {"exist_key":2}
  ]
}

• Result of jsonpath is nil There are cases when jsonpath value is nil:

  • Value in JSON is nil

  • There is no such key in JSON

Example:

  fromJson:
      jsonPath: $.null_key
      defaultValue: -1
      valueType: INT

the result of above Jsonpath is -1 because $.null_key returning nil

• Result of jsonpath is empty array

    fromJson:
        jsonPath: $.empty_array
        defaultValue: 0.0
        valueType: FLOAT

  the result of above Jsonpath is [0.0] because $.empty_array returning empty so it will use default value

• Result of jsonpath is array, where some of its value is null

    fromJson:
        jsonPath: $.instances_with_null[*].petal_width
        defaultValue: -1
        valueType: INT

  the result of above Jsonpath is [0.4,-1,0.5], because the original jsonpath result [0.4,null,0.5] containing null value, the default value is used to replace null value

Expression

An expression is a single line of code which should return a value. Standard transformer uses expression as a flexible way of calculating values to be used in variable initialization or any other operations.

For example:

Expression can be used for initialising variable value

variables:
  - currentTime:
      expression: now() 
  - currentHour:
      expression: currentTime.Hour() 

Expression can be used for updating column value

 updateColumns:
    column: "s2id"
    expression: getS2ID(df.Col('lat'), df.Col('lon'))

For full list of standard transformer built-in functions, please check:

Standard Transformer Expressions

Input Stage

At the input stage, users specify all the data dependencies that are going to be used in subsequent stages. There are 4 operations available in these stages:

1. Table creation

   • Table Creation from Feast Features

   • Table Creation from Input Request

   • Table Creation from File

2. Variable declaration

3. Encoder declaration

4. Autoload

Table Creation

Table is the main data structure within the standard transformer. There are 3 ways of creating table in standard transformer:

Table Creation from Feast Features

This operation creates one or more tables containing features from Feast. This operation is already supported in Merlin 0.10. The key change to be made is to adapt the result of operation. Previously, the features retrieved from feast is directly enriched to the original request body to be sent to the model. Now, the operation only outputs as internal table representation which can be accessible by subsequent transformation steps in the pipeline.

Additionally, it should be possible for users to give the features table a name to ease referencing the table from subsequent steps.

Following is the syntax:

 feast:
     - tableName:       # Specify the output table name

       project:          # Name of project in feast where the features located

       source:           # Source for feast (REDIS or BIGTABLE)

       entities:        # List of entities

         - name:          # Entity Id

           valueType:     # Entity Value Type
          
           # The entity value will be retrieved either using jsonPath or expression configuration below:  
           jsonPathConfig: 

             jsonPath:       # Json path in the incoming request container the entity value

             defaultValue:   # (Optional) Default value if value for the jsonPath is nil or empty 

             valueType:      # Type of default value, mandatory to specify if default value is exist

           jsonPath:      # Json path in the incoming request containing the entity value (Deprecated)

           expression:    # Expression provided by user which return entity values

       features:        # List of features to be retrieved

         - name:          # feature name

           defaultValue:  # default value if the feature is not available

below is the sample of feast input:

  feast:
        - tableName: table_1
          project: sample
          source: BIGTABLE
          entities:
            - name: merchant_uuid
              valueType: STRING
              jsonPathConfig:
                  jsonPath: $.merchant_uuid
                  defaultValue: -1
                  valueType: INT
            - name: customer_id
              valueType: STRING
              expression: customer_id
          features:
            - name: sample_driver:order_count
              valueType: DOUBLE
              defaultValue: '90909'

There are two ways to get/retrieve features from feast in merlin standard transformer: * Getting the features values from feast GRPC URL * By direcly querying from feast storage (Bigtable or Redis). For this, you need to add extra environment variables in standard transformer * REDIS. Set FEAST_REDIS_DIRECT_STORAGE_ENABLED value to true * BIGTABLE. Set FEAST_BIGTABLE_DIRECT_STORAGE_ENABLED value to true

For detail explanation of environment variables in standard transformer, you can look this section

Table Creation from Input Request

This step is generic table creation that allows users to define one or more tables based on value from either JSON payload, result of built-in expressions, or an existing table. Following is the syntax for table input:

  tables:

      - name:         # Table name

        baseTable:         # create a base table either from a JSON array of object or from existing table

          fromJson:        # create a table based on an array of objects within JSON payload, the object key will be column name.

              jsonPath:       # JSONPath to array of object in the JSON payload

              defaultValue:   # Fallback value if value for jsonpath is nil or empty   

              addRowNumber:   # True/false, add column called "row_number" which contains row number

          fromTable:       # Create base table from an existing table

              tableName:     # Source table name

          columns:          # List of columns to be added in the table, it's possible to have 0 columns. The columns will override existing column defined in the baseTable

                          # The number of row in the first column determines the table size so put the longest column first

              - name:           # Column name

                fromJson:        # Get column values from json path

                  jsonPath:       # JSONPath to array of object in the JSON payload

                  defaultValue:   # Fallback value if value for jsonpath is nil or empty    

                expression:      # Assign result from expression to the column value

sample:

  - tables:
        - name: table_2
          baseTable:
            fromTable:
              tableName: table_1
          columns:
            - name: col_1
              fromJson:
                  jsonPath: $.drivers[*].id
            - name: col_2
              expression: table.Col('rating')
        - name: table_3
          baseTable:
            fromJson:
              jsonPath: $.drivers[*]
          columns:
            - name: col_1
              fromJson:
                  jsonPath: $.drivers[*].id
            - name: col_2
              expression: table.Col('rating')

Table Creation from File

This operation allows user to create a static table from a file. For example, user might choose to load a table with a list of public holidays for the year. As the data will be loaded into memory, it is strongly advised to keep the total size of all files within 50mb. Also, each file shall only contain information for 1 table.

Supported File Format

There are 2 types of files are currently supported:

• csv: For this file type, only comma (,) may be used as delimiter. The first line shall also contain a header, which gives each column a unique name.

• parquet

Supported File Storage Location

Currently, files must first be uploaded to a preferred GCS bucket in gods-* project. The file will be read once during deployment.

Supported Column Types

Only basic types for the columns are supported, namely: String, Integer, Float and Boolean

The types of each column are auto-detected, but may be manually set by the user (please ensure type compatibility).

How to use

In order to use this feature, firstly, these files will have to be loaded into GCS buckets in gods-* projects in order to be linked.

Then, use the syntax below to define the specifications:

```
tables:
- name:     # Table name  
  baseTable:      
    fromFile:
      format: CSV    # others: PARQUET
      uri:  # GCS uri to the location of the file in gods-* project
      schema:   # this part is used to manually set column type
      - name: col_1        # name of column
        type: STRING     #others: INT, FLOAT, BOOL
…         
      - name: col_2
        type: INT
```

Variable

Variable declaration is used for assigning literal value or result of a function into a variable. The variable declaration will be executed from top to bottom and it’s possible to refer to the declared variable in subsequent variable declarations. Following are ways to set value to variable.

• Literal Specifiying literal value to variable. By specifying literal values user needs to specify what is the type for that variable. Types that supported for this:

  • String

  • Int

  • Float

  • Bool for example:

    - variables:
        - name: var_1
          literal:
            intValue: 3
        - name: var_2
          literal:
            floatValue: 2.2
        - name: var_3
          literal:
            boolValue: true
        - name: var_4
          literal:
            stringValue: stringVal
  

• Jsonpath Value of variable is obtained from request/model response payload by specifying jsonpath value, e.g

    - variables:
        - name: var_5
          jsonPathConfig: 
            jsonPath: $.rating
            defaultValue: -1
            valueType: INT
        - name: var_6
          jsonPath: $rating # deprecated

• Expression Value of variable is obtained from expression, e.g

    - variables:
        - name: var_7
          jsonPathConfig:
            jsonPath: $.customer_id
        - name: var_8
          expression: var_7

Encoders

In order to encode data in the transformation stage, we need to first define an encoder by giving it a name, and defining the associated configurations.

The syntax of encoder declaration is as follows:

- encoders: 

    - name:           #name of encoder 1

      <encoder 1 specs>

    - name:          #name of encoder 2

      <encoder 2 specs>

There are 2 types of encoder currently available:

Ordinal encoder: For mapping column values from one type to another

Cyclical encoder: For mapping column values that have a cyclical significance. For example, Wind directions, time of day, days of week

Ordinal Encoder Specification

The syntax to define an ordinal encoder is as follows:

ordinalEncoderConfig: 

  defaultValue:         #default value

  targetValueType:      #target value type. i.e. INT, FLOAT, BOOL or STRING

  mapping: 

    <mapping value 1>

    …

    <mapping value n>

There are currently 4 types of target value supported. The following table shows the syntax to use for each type:

Value Type	Syntax
Integer	INT
Float	FLOAT
Boolean	BOOL
String	STRING

See below for a complete example on how to declare an ordinal encoder

- encoders: 
    - name: vehicle_mapping 
      ordinalEncoderConfig: 
          defaultValue: '0' 
          targetValueType: INT 
          mapping: 
            suv: '1' 
            sedan: '2'

Cyclical Encoder Specification

Cyclical encoder are useful for encoding columns that has cyclical significance. By encoding such columns cyclically, you can ensure that the values representing the end of a cycle and the start of the next cycle does not jump abruptly. Some examples of such data are:

• Hours of the day

• Days of the week

• Months in a year

• Wind direction

• Seasons

• Navigation Directions

The syntax to define an cyclical encoder is as follows:

cyclicalEncoderConfig:
  <Encode By>

There are 2 ways to encode the column:

1. By epoch time: Unix Epoch time is the number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT). By using this option, we assume that the time zone to encode in will be UTC. In order to use this option you only need to define the period of your cycle to encode.

2. By range: This defines the base range of floating point values representing a cycle. For example, one might define wind directions to be in the range of 0 to 360 degrees, although the actual value may be >360 or <0.

To encode by epoch time, use the following syntax:

cyclicalEncoderConfig:
  byEpochTime:
    periodType: HOUR #HOUR, DAY, WEEK, MONTH, QUARTER, HALF, YEAR

Period type defines the time period of a cycle. For example, HOUR means that a new cycle begins every hour and DAY means that a new cycle begins every day.

NOTE: If you choose to encode by epoch time, the granularity is per seconds. If you need different granularity, you can modify the values in the epoch time column accordingly or choose to encode by range.

To encode by range, use the following syntax:

cyclicalEncoderConfig:
  byRange:
    min: FLOAT
    max: FLOAT

Do note that the min and max values are Float. The range is inclusive for the min and exclusive for the max, since in a cycle min and max will represent the same phase. For example, you can encode the days of a week in the range of [1, 8), where 8 and 1 both represents the starting point of a cycle. You can then represent Monday 12am as 1 and Sunday 12pm as 7.5 and so on.

See below for complete examples on how to declare a cyclical encoder:

By epoch time:

-encoders: 
  -name: payday_trend
   cyclicalEncoderConfig:
     byEpochTime:
       periodType: MONTH

By range:

-encoders: 
  -name: wind_dir 
   cyclicalEncoderConfig:
      byRange:
        min: 0
        max: 360

Input/Output Examples By epoch time: Period of a day

col	col_x	col_y	remarks
1644278400	1	0	8 Feb 2022 00:00:00 UTC
1644300000	0	1	8 Feb 2022 06:00:00 UTC
1644451200	-1	0	8 Feb 2022 12:00:00 UTC
1644343200	0	-1	8 Feb 2022 18:00:00 UTC
1644364800	1	0	9 Feb 2022 00:00:00 UTC
1644451200	1	0	10 Feb 2022 00:00:00 UTC

By range: 0 to 360 (For example wind directions)

col	col_x	col_y
0	1	0
90	0	1
180	-1	0
270	0	-1
360	1	0
420	0	1
-90	0	-1

To learn more about cyclical encoding, you may find this page useful: Cyclical Encoding

Autoload

Autoload declares tables and variables that need to be loaded to standard transformer runtime from incoming request/response. This operation is only applicable for upi_v1 protocol. Below is specification of autoload

autoload:
  tableNames:
    - table_name_1
    - table_name_2
  variableNames:
    - var_name_1
    - var_name_2

tableNames and variableNames are fields that list table name and variables declaration. If autoload is part of preprocess pipeline, it will try to load those declared table and variables from request payload, otherwise it will load from model response payload.

Transformation Stage

In this stage, the standard transformers perform transformation to the tables created in the input stage so that its structure is suitable for the output. In the transformation stage, users operate mainly on tables and are provided with 2 transformation types: single table transformation and table join. Each transformation declared in this stage will be executed sequentially and all output/side effects from each transformation can be used in subsequent transformations. There are two types of transformations in standard transformer: * Table Transformation * Table Join

Table Transformation

Table transformation performs transformation to a single input table and creates a new table. The transformation performed to the table is defined within the “steps” field and executed sequentially.

  tableTransformation:

    inputTable:              # name of the input table

    outputTable:             # name of the output table

    steps:                   # list of transformation steps, it will be executed sequentially

     - <step 1 specification>

     - <step 2 specification>

Following are the operation available for table transformation:

Drop Column

This operation will drop one or more column

 tableTransformation:

   inputTable: myTable

   outputTable: myTransformedTable

   steps:

     - dropColumns: ["id"]

Select Column

This operation will reorder and optionally drop non-selected column

 tableTransformation:

   inputTable: myTable

   outputTable: myTransformedTable

   steps:

     - selectColumns: ["lat", "lon", "total_trip"]

Sort Operation

This operation will sort the table using the defined column and ordering

tableTransformation:
  inputTable: myTable
  outputTable: myTransformedTable
  steps:
    - sort:
        - column: id
          order: ASC
        - column: total_trip
          order: DESC

Rename Columns

This operation will rename one column into another

tableTransformation:
     inputTable: myTable
     outputTable: myTransformedTable
     steps:
     - renameColumns:
         "total_trip": "totalTrip"

Update Columns

Adding column or modifying column in-place using expressions

tableTransformation:
     inputTable: myTable
     outputTable: myTransformedTable
     steps:
     - updateColumns:
        - column: "s2id"
          expression: S2ID(myTable.Col('lat'), myTable.Col('lon'), 12)
        - column: "col2"
          conditions:
          - rowSelector: myTable.Col('col1') * 2 > 10
            expression: myTable.Col('col1')
          - default:
              expression: -1

There are two ways to update columns:

• Update all rows in the column. You need to specify columnand expression. column determines which column to be updated and expression determines the value that will be used to update the column. Value produced by the expression must be a scalar or a series that has the same length as the other columns. Following the example::

    - updateColumns:
      - column: "customer_id"
        expression: "cust_1" # the value is scalar and will be broadcasted to all the row
      - column: "s2id"
        expression: S2ID(myTable.Col('lat'), myTable.Col('lon'), 12) # the value is array or series that the length should be the same with the rest of the columns in a table 

• Update subset of rows in the columns given some row selector condition. For this users can set multiple rowSelector with expression and also default value if none of conditions are match. For example users have following table

customer_id	customer_age	total_booking_1w
1234	60	8
4321	23	4
1235	17	4

Users want to create new column customer_segment with certain rules:

1. Customer that older than 55, the customer_segment will be retired

2. Customer that has age between 30 - 55, the customer_segment will be matured

3. Customer that has age between 22 - 30, the customer_segment will be productive

4. Customer that has age < 22, the customer_segment will be non-productive

Based on those rules we can translate this to standard transformer config:

tableTransformation:
     inputTable: myTable
     outputTable: myTransformedTable
     steps:
     - updateColumns:
        - column: "customer_segment"
          conditions:
          - rowSelector: myTable.Col('customer_age') > 55
            expression: "retired"
          - rowSelector: myTable.Col('customer_age') >= 30
            expression: "matured"
          - rowSelector: myTable.Col('customer_age') >= 22
            expression: "productive"
          - default:
              expression: "non-productive"

All rowSelector conditions are working like if else statement. rowSelector condition must be returning boolean or series of boolean, default will be executed if none of the rowSelector conditions are matched.

Filter Row

Filter row is an operation that will filter rows in a table based on given condition. Suppose users have this following table

customer_id	customer_age	total_booking_1w
1234	60	8
4321	23	4
1235	17	4

and users want to show only records that have total_booking_1w less than 5. To achieve that users need to use filterRow operation like below configuration:

tableTransformation:
     inputTable: myTable
     outputTable: myTransformedTable
     steps:
     - filterRow:
        condition: myTable.Col('total_booking_1w') < 5

Slice Row

Slice row is an operation to slice a table based on start(lower bound) and end index(upper bound) that given by the user. The result includes starting index but excluding end index. Below is the example of this operation

tableTransformation:
     inputTable: myTable
     outputTable: myTransformedTable
     steps:
     - sliceRow:
        start: 0
        end: 4

Value of start end end can be null or negative. Following are the behaviour:

• Null value of start means that start value is 0

• Null value of end means that end value is number of rows in a table

• Negative value of start or end means that the value will be (number of row + start) or (number of row + end). Suppose you set start -5 and end -1 and number of row is 10, so start value will be 5 and end will be 9

Encode Column

This operation will encode the specified columns with the specified encoder defined in the input step.

tableTransformation:
    inputTable: myTable
    outputTable: myTransformedTable
    steps:
      - encodeColumns: 
          - columns: 
                - vehicle 
                - previous_vehicle 
            encoder: vehicle_mapping

Scale Column

This operation will scale a specified column using scalers. At the moment 2 types of scalers are available:

• Standard Scaler

• Min-max Scaler

Standard Scaler In order to use a standard scaler, the mean and standard deviation (std) of the respective column to be scaled should be computed beforehand and provided in the specification. The syntax for scaling a column with a standard scaler is as follows:

tableTransformation:
    inputTable: myTable
    outputTable: myTransformedTable
    steps:
        - scaleColumns: 
            - column: rank 
              standardScalerConfig: 
                  mean: 0.5 
                  std: 0.2

Min-Max Scaler In order to use a min-max scaler, the minimum and maximum value for the column to scale to must be defined in the specification. The syntax for scaling a column with a min-max scaler is as follows:

tableTransformation:
    inputTable: myTable
    outputTable: myTransformedTable
    steps:
        - scaleColumns: 
            - column: rating 
               minMaxScalerConfig: 
                min: 1 
                max: 5

Join Operation

This operation joins 2 tables, as defined by “leftTable” and “rightTable” parameters, into 1 output table given a join column and method of join. The join column must exist in both the input tables. The available method of join are: * Left join * Concat Column * Cross join * Inner Join * Outer join * Right join

tableJoin:
 leftTable: merchant_table
 rightTable: customer_table
 outputTable: merchant_customer_table
 how: LEFT # LEFT, INNER , RIGHT, CROSS, OUTER, CONCAT_COLUMN
 onColumn: merchant_id

Output Stage

At this stage, both the preprocessing and postprocessing pipeline should create an output. The output of preprocessing pipeline will be used as the request payload to be sent as model request, whereas output of the postprocessing pipeline will be used as response payload to be returned to downstream service / client. There are 3 types of output specifications:

• JSON Output. Applicable for http_json protocol and both preprocess and postprocess output

• UPIPreprocessOutput. Applicable only for upi_v1 protocol and preprocess output

• UPIPostprocessOutput. Applicable only for upi_v1 protocol and postprocess output

JSON Output - User-defined JSON template

Users are given freedom to specify the transformer’s JSON output structure. The syntax is as follows:

output:

-  jsonOutput:

     jsonTemplate:

       baseJson:            # Base JSON Template, the value can be "fromJson" or "fromTable"                     

         fromJson:          # Copy JSON object pointed by the source and jsonPath

           jsonPath:        # Path to JSON field to be copied from in the source JSON

         fromTable:              # Create json payload from a table

           tableName:            # Source table name

           format:               # json output format, possible format are (based on https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.to_json.html): RECORD, VALUES, SPLIT

       fields:                   # list of JSON field to be included, fields defined here will override JSON field in the base JSON

          -   fieldName :        # field name

              fromJson:             # Copy json field from RAW_REQUEST / MODEL_RESPONSE

                jsonPath:           # json path of the field to be copied from source JSON payload

              fromTable:              # Create json from a table

                tableName:            # Source table name

                format:               # json output format, possible format are (based on https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.to_json.html): RECORD, VALUES, SPLIT

                expression:       # populate the field with value from result of an expression

          -   fieldName: 

                fields:               # it's also possible to have a nested JSON field

                    - <nested field>

Similar to the table creation specification, users can specify the “baseJson” as the base json structure and override it using “fields” configuration.

The field_value above can be configured to retrieve from 3 sources:

• From JSON

• From Table

• From Expression

From JSON

In the example below, “output” field will be set to the “predictions” field from the model response.

jsonOutput:
   jsonTemplate:
     fields:
        - fieldName: output
          fromJson:
            jsonPath: $.model_response.predictions

From Table

Users can populate JSON fields using values from a table. The table can be rendered into 3 JSON formats: RECORD, VALUES, and SPLIT. Note that if “fromTable” is used as “baseJson” it will use the table name as the json field.

For example, given following customerTable:

customer_id	customer_age	total_booking_1w
1234	34	8
4321	23	4
1235	17	4

Depending on the json format, it will render different result JSON

• RECORD Format

  outputStage:
    jsonOutput:
      jsonTemplate:
        fields:
        - fieldName: instances
          fromTable:
             tableName: customerTable
             format: RECORD

JSON Result:

        {
           "instances" : [
               [
                   {
                       "customer_id" : 1234,
                       "customer_age" : 34,
                       "total_booking_1w": 8
                   },
                   {
                       "customer_id" : 4321,
                       "customer_age" : 23,
                       "total_booking_1w": 4
                   },
                   {
                       "customer_id" : 1235,
                       "customer_age" : 17,
                       "total_booking_1w": 4
                   }
               ]
           ]
        }

• VALUES Format

  outputStage:
    jsonOutput:
      jsonTemplate:
        fields:
        - fieldName: instances
          fromTable:
             tableName: customerTable
             format: VALUES

JSON Result:

        {
            "instances":[
                [
                    [1234, 34, 8],
                    [4321, 23, 4],
                    [1235, 17, 4]
                ]
            ]
        }

• SPLIT Format

  outputStage:
    jsonOutput:
      jsonTemplate:
        fields:
        - fieldName: instances
          fromTable:
             tableName: customerTable
             format: SPLIT

JSON Result:

      {
         "instances" : {
             "data": [
                 [1234, 34, 8],
                 [4321, 23, 4],
                 [1235, 17, 4]
             ],
             "columns" : ["customer_id", "customer_age", "total_booking_1w"]
         }
      }

UPIPreprocessOutput

UPIPreprocessOutput is output specification only for upi_v1 protocol and preprocess step. This output specification will create operation that convert defined tables to UPI request interface. Below is the specification

upiPreprocessOutput:
  predictionTableName: table_1
  transformerInputTableNames:
    - input_table_1
    - input_table_2

This specification will convert content of predictionTableName into UPI table

message Table {
    string name = 1;
    repeated Column columns = 2;
    repeated Row rows = 3;
}
message Column {
    string name = 1;
    Type type = 2;
}
message Row {
   string row_id = 1;
   repeated Value values = 2;
}
message Value {
    double double_value = 1;
    int64 integer_value = 2;
    string string_value = 3;
    bool is_null = 10;
}

and then set field prediction_table from this UPI Request interface

message PredictValuesRequest { 
  Table prediction_table = 1;
  TransformerInput transformer_input = 4;
  string target_name = 2;
  repeated Variable prediction_context = 3;

  RequestMetadata metadata = 10;
}

transformerInputTableNames are list of table names that will be converted into UPI Table. These values will be assigned into field transformer_input.tables field. The rest of the fields will be carried on from the incoming reques payload.

UPIPostprocessOutput

UPIPostprocessOutput is output specification only for upi_v1 protocol and postprocess step. This output specification will create operation that convert defined tables to UPI response interface. Below is the specification

upiPostprocessOutput:
  predictionResultTableName: table_name_1

This specification will convert content of predictionResultTableName into UPI table and assigned it to field prediction_result_table in this UPI Response interface like below

message PredictValuesResponse {
  Table prediction_result_table = 1;
  string target_name = 2;
  repeated Variable prediction_context = 3;
  ResponseMetadata metadata = 10;
}

The rest of the fields will be carried on from model predictor response

Deploy Standard Transformer using Merlin UI

Once you logged your model and it’s ready to be deployed, you can go to the model deployment page.

Here’s the short video demonstrating how to configure the Standard Transformer:

1. As the name suggests, you must choose Standard Transformer as Transformer Type.

2. The Retrieval Table panel will be displayed. This panel is where you configure the Feast Project, Entities, and Features to be retrieved.

   1. The list of Feast Entity depends on the selected Feast Project

   2. Similarly, the list of Feast Feature also depends on the configured entities

3. You can have multiple Retrieval Table that can retrieve a different kind of entities and features and enrich the request to your model at once. To add it, simply click Add Retrieval Table, and new Retrieval Table panel will be displayed and ready to be configured.

4. You can check the Transformer Configuration YAML specification by clicking See YAML configuration. You can copy and paste this YAML and use it for deployment using Merlin SDK.

   1. To read more about Transformer Configuration specification, please continue reading.

5. You can also specify the advanced configuration. These configurations are separated from your model.

   1. Request and response payload logging

   2. Resource request (Replicas, CPU, and memory)

   3. Environment variables (See supported environment variables below)

Deploy Standard Transformer using Merlin SDK

Make sure you are using the supported version of Merlin SDK.

> pip install merlin-sdk -U
> pip show merlin-sdk

Name: merlin-sdk
Version: 0.10.0
...

You need to pass transformer argument to the merlin.deploy() function to enable and deploy your standard transformer.

standard_transformer_deployment.py

from merlin.resource_request import ResourceRequest
from merlin.transformer import StandardTransformer

# Specify the path to transformer config YAML file
transformer_config_path = "transformer_config.yaml"

# Create the transformer resources requests config
resource_request = ResourceRequest(min_replica=0, max_replica=1,
                                   cpu_request="100m", memory_request="200Mi")

# Create the transformer object
transformer = StandardTransformer(config_file=transformer_config_path,
                                  enabled=True,
                                  resource_request=resource_request)

# Deploy the model alongside the transformer
endpoint = merlin.deploy(v, transformer=transformer)

Standard Transformer Environment Variables

Below are supported environment variables to configure your Transformer.

Name	Description	Default Value
LOG_LEVEL	Set the logging level for internal system. It doesn’t effect the request-response logging. Supported value: DEBUG, INFO, WARNING, ERROR.	INFO
FEAST_FEATURE_STATUS_MONITORING_ENABLED	Enable metrics for the status of each retrieved feature.	false
FEAST_FEATURE_VALUE_MONITORING_ENABLED	Enable metrics for the summary value of each retrieved feature.	false
FEAST_BATCH_SIZE	Maximum number of entities values that will be passed as a payload to feast. For example if you want to get features from 75 entities values and FEAST_BATCH_SIZE is set to 50, then there will be 2 calls to feast, first call request features from 50 entities values and next call will request features from 25 entities values.	50
FEAST_CACHE_ENABLED	Enable cache response of feast request	true
FEAST_CACHE_TTL	Time to live cached features, if TTL is reached the cached will be expired. The value has format like this [$number][$unit] e.g 60s, 10s, 1m, 1h	60s
CACHE_SIZE_IN_MB	Maximum capacity of cache from allocated memory. Size is in MB	100
FEAST_REDIS_DIRECT_STORAGE_ENABLED	Enable features retrieval by querying direcly from redis	false
FEAST_REDIS_POOL_SIZE	Number of redis connection established in one replica of standard transformer	10
FEAST_REDIS_READ_TIMEOUT	Timeout for read commands from redis. If reached commands will fails	3s
FEAST_REDIS_WRITE_TIMEOUT	Timeout for write commands to redis. If reached commands will fails	3s
FEAST_BIGTABLE_DIRECT_STORAGE_ENABLED	Enable features retrieval by querying direcly from bigtable	false
FEAST_BIGTABLE_POOL_SIZE	Number of bigtable grpc connections established in one replica of standard transformer
FEAST_TIMEOUT	Timeout of feast request	1s
FEAST_HYSTRIX_MAX_CONCURRENT_REQUESTS	Maximum concurrent requests when calling feast	100
FEAST_HYSTRIX_REQUEST_VOLUME_THRESHOLD	Threshold of error percentage, once breached circuit will be open	100
FEAST_HYSTRIX_SLEEP_WINDOW	Sleep window is duration of rejecting calling feast once the circuit is open	1s
FEAST_HYSTRIX_ERROR_PERCENT_THRESHOLD	Threshold of number of request to model predictor	25
FEAST_SERVING_KEEP_ALIVE_ENABLED	Flag to enable feast keep alive	true
FEAST_SERVING_KEEP_ALIVE_TIME	Duration of interval between keep alive PING	60s
FEAST_SERVING_KEEP_ALIVE_TIMEOUT	Duration of PING that considered as TIMEOUT	5s
MERLIN_DISABLE_LIVENESS_PROBE	Disable liveness probe of transformer if set to true
MODEL_TIMEOUT	Timeout duration of model prediction	1s
MODEL_HYSTRIX_MAX_CONCURRENT_REQUESTS	Maximum concurrent requests when calling model predictor	100
MODEL_HYSTRIX_ERROR_PERCENTAGE_THRESHOLD	Threshold of error percentage, once breached circuit will be open	25
MODEL_HYSTRIX_REQUEST_VOLUME_THRESHOLD	Threshold of number of request to model predictor	100
MODEL_HYSTRIX_SLEEP_WINDOW_MS	Sleep window is duration of rejecting calling model predictor once the circuit is open	10
MODEL_GRPC_KEEP_ALIVE_ENABLED	Flag to enable UPI_V1 model predictor keep alive	false
MODEL_GRPC_KEEP_ALIVE_TIME	Duration of interval between keep alive PING	60s
MODEL_GRPC_KEEP_ALIVE_TIMEOUT	Duration of PING that considered as TIMEOUT	5s