Schema

Each table in Pinot is associated with a Schema. A schema defines what fields are present in the table along with the data types. The schema is stored in the Zookeeper along with the table configuration.

Categories

A schema also defines what category a column belongs to. Columns in a Pinot table can be broadly categorized into three categories -

Data Types

Data type helps in determining the operations which can be performed on the column. The following data types are supported by Pinot

Date Time Fields

Since pinot doesn't have a dedicated DATETIME datatype support, the user needs to input time in either STRING, LONG, or INT format. However, Pinot needs to convert the date into an understandable format such as epoch timestamp to do operations.

To achieve this conversion, users need to provide the format of the date along with the data type in schema. The syntax of the format is timeSize:timeUnit:timeFormat:pattern .

• time size - the size of the time unit. This size is multiplied to the value present in the time column to get an actual timestamp. eg: if timesize is 5 and value in time column is 4996308 minutes. The value that will be converted to epoch timestamp will be 4996308 * 5 * 60 * 1000 = 1498892400000 milliseconds. If your date is not in EPOCH format, this value is not used and can be set to 1 or any other integer.

• time unit - one of TimeUnit enum values. e.g. HOURS , MINUTES etc. If your date is not in EPOCH format, this value is not used and can be set to MILLISECONDS or any other unit.

• timeFormat - can be either EPOCH or SIMPLE_DATE_FORMAT. If it is SIMPLE_DATE_FORMAT, the pattern string is also specified.

• pattern - This is optional and is only specified when the date is in SIMPLE_DATE_FORMAT . The pattern should be specified using the java SimpleDateFormat representation. e.g. 2020-08-21 can be represented as yyyy-MM-dd.

Here are some sample date-time formats you can use in the schema- 1:MILLISECONDS:EPOCH - used when timestamp is in the epoch milliseconds and stored in LONG format 1:HOURS:EPOCH - used when timestamp is in the epoch hours and stored in LONG or INT format 1:DAYS:SIMPLE_DATE_FORMAT:yyyy-MM-dd - when date is in STRING format and has the pattern year-month-date. e.g. 2020-08-21 1:HOURS:SIMPLE_DATE_FORMAT:EEE MMM dd HH:mm:ss ZZZ yyyy - when date is in STRING format. e.g. s Mon Aug 24 12:36:50 America/Los_Angeles 2019

Creating a Schema

First, Make sure your cluster is up and running. Let's create a schema and put it in a JSON file. For this example, we have created a schema for flight data.

flights-schema.json
{
  "schemaName": "flights",
  "dimensionFieldSpecs": [
    {
      "name": "flightNumber",
      "dataType": "LONG"
    },
    {
      "name": "tags",
      "dataType": "STRING",
      "singleValueField": false,
      "defaultNullValue": "null"
    }
  ],
  "metricFieldSpecs": [
    {
      "name": "price",
      "dataType": "DOUBLE",
      "defaultNullValue": 0
    }
  ],
  "dateTimeFieldSpecs": [
    {
      "name": "millisSinceEpoch",
      "dataType": "LONG",
      "format": "1:MILLISECONDS:EPOCH",
      "granularity": "15:MINUTES"
    },
    {
      "name": "hoursSinceEpoch",
      "dataType": "INT",
      "format": "1:HOURS:EPOCH",
      "granularity": "1:HOURS"
    },
    {
      "name": "dateString",
      "dataType": "STRING",
      "format": "1:DAYS:SIMPLE_DATE_FORMAT:yyyy-MM-dd",
      "granularity": "1:DAYS"
    }
  ]
}

Then, we can upload the sample schema provided above using either bash command or REST API call.

bin/pinot-admin.sh AddSchema -schemaFile flights-schema.json -exec
​
OR
​
bin/pinot-admin.sh AddTable -schemaFile flights-schema.json -tableFile flights-table.json -exec

curl -F schemaName=@transcript-schema.json  localhost:9000/schemas

Check out the schema in the Rest API to make sure it was successfully uploaded