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Schema

Schema is used to define the names, data types, and other information for the columns of a Pinot table.

The Pinot schema is composed of:

Field Description
schemaName Defines the name of the schema. This is usually the same as the table name. The offline and the real-time table of a hybrid table should use the same schema.
dimensionFieldSpec A dimensionFieldSpec is defined for each dimension column. For more details, scroll down to DimensionFieldSpec.
metricFieldSpec A metricFieldSpec is defined for each metric column. For more details, scroll down to MetricFieldSpec.
dateTimeFieldSpec A dateTimeFieldSpec is defined for the time columns. There can be multiple time columns. For more details, scroll down to DateTimeFieldSpec.

{% code title="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": "EPOCH",
      "granularity": "15:MINUTES"
    },
    {
      "name": "hoursSinceEpoch",
      "dataType": "INT",
      "format": "EPOCH|HOURS",
      "granularity": "1:HOURS"
    },
    {
      "name": "dateString",
      "dataType": "STRING",
      "format": "SIMPLE_DATE_FORMAT|yyyy-MM-dd",
      "granularity": "1:DAYS"
    }
  ]
}

{% endcode %}

The above json configuration is the example of Pinot schema derived from the flight data. As seen in the example, the schema is composed of 4 parts: schemaName, dimensionFieldSpec, metricFieldSpec, and dateTimeFieldSpec. Below is a detailed description of each type of field spec.

DimensionFieldSpec

A dimensionFieldSpec is defined for each dimension column. Here's a list of the fields in the dimensionFieldSpec:

Property Description
name Name of the dimension column.
dataType Data type of the dimension column. Can be INT, LONG, FLOAT, DOUBLE, BOOLEAN, TIMESTAMP, STRING, BYTES,JSON.
defaultNullValue Represents null values in the data, since Pinot doesn't support storing null column values natively (as part of its on-disk storage format). If not specified, an internal default null value is used as listed here.
singleValueField Boolean indicating if this is a single-valued or a multi-valued column. Multi-valued column is modeled as a list, where the order of the values are preserved and duplicate values are allowed. Individual rows don’t necessarily have the same number of values. Typical use case for this would be a column such as skillSet for a person (one row in the table) that can have multiple values such as Real Estate, Mortgages. The default null value for a multi-valued column is a single defaultNullValue, e.g. [Integer.MIN_VALUE].

Internal default null values for dimension

Data Type Internal Default Null Value
INT ​Integer.MIN_VALUE​
LONG ​Long.MIN_VALUE​
FLOAT ​Float.NEGATIVE_INFINITY​
DOUBLE ​Double.NEGATIVE_INFINITY​
BOOLEAN 0 (false)
TIMESTAMP 0 (1970-01-01 00:00:00 UTC)
STRING "null"
BYTES byte array of length 0
JSON "null"

MetricFieldSpec

A metricFieldSpec is defined for each metric column. Here's a list of fields in the metricFieldSpec

Property Description
name Name of the metric column
dataType Data type of the column. Can be INT, LONG, FLOAT, DOUBLE, BIG_DECIMAL, BYTES (for specialized representations such as HLL, TDigest, etc, where the column stores byte serialized version of the value)
defaultNullValue Represents null values in the data. If not specified, an internal default null value is used, as listed here.

Internal default null values for metric

Data Type Internal Default Null Value
INT 0
LONG 0
FLOAT 0.0
DOUBLE 0.0
BIG_DECIMAL 0.0
BYTES byte array of length 0

DateTimeFieldSpec

A dateTimeFieldSpec is used to define time columns of the table. The following fields can be configured in the date time field spec -

Property Description
name Name of the date time column
dataType Data type of the date time column. Can be STRING, INT, LONG or TIMESTAMP
format

The format in which the datetime is present in the column. Refer to Date time formats for supported formats.
granularity

The granularity in which the column is bucketed. The syntax of granularity is
bucket size:bucket unit
For example, the format can be milliseconds 1:MILLISECONDS:EPOCH, but bucketed to 15 minutes i.e. we only have one value for every 15 minute interval, in which case granularity can be specified as 15:MINUTES. Currently it is just for documentation purpose, and Pinot won't automatically round the time value to the specified granularity.
defaultNullValue

Represents null values in the data. If not specified, an internal default null value is used. If date time is in String format, the default value will be null or if timestamp then it is epoch 0 (i.e. 1970-01-01 00:00:00).

For the main time column of the table (time column specified in the segmentsConfig

in the table config), the main time column value must be in the range of 1971-01-01 UTC to 2071-01-01 UTC for segment management purpose (e.g. retention, time boundary). If the specified default null value is not within this range, segment creation time is used.

New DateTime Formats

In the pinot master (0.12.0-SNAPSHOT), We have simplified date time formats for the users. The formats now follow the pattern - timeFormat|pattern/timeUnit|[timeZone/timeSize] . The fields present in [] are completely optional. timeFormat can be one of EPOCH , SIMPLE_DATE_FORMAT or TIMESTAMP .

  • TIMESTAMP - This represents timestamp in milliseconds. It is equivalent to specifying EPOCH:MILLISECONDS:1
    Examples -
    • TIMESTAMP
  • EPOCH - This represents time in timeUnit since 00:00:00 UTC on 1 January 1970, where timeUnit is one of TimeUnit enum values, e.g. HOURS , MINUTES etc. You can also specify the timeSize parameter. This size is multiplied to the value present in the time column to get an actual timestamp. e.g. 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. In simplest terms, EPOCH|SECONDS|5 denotes the count of intervals of length 5 seconds from epoch 0 to now.

    Examples -
    • EPOCH - Defaults to MILLISECONDS (only in master branch)
    • EPOCH|SECONDS
    • EPOCH|SECONDS|5
  • SIMPLE_DATE_FORMAT - This represents time in the string format. The pattern should be specified using the Joda's DateTimeFormat representation. In the master branch build, if no pattern is specified, we use ISO 8601 DateTimeFormat to parse the date times. Optionals are supported with ISO format so users can specify date time string in yyyy or yyyy-MM or yyyy-MM-dd and so on

    You can also specify optional timeZone parameter which is the ID for a TimeZone, either an abbreviation such as PST, a full name such as America/Los_Angeles, or a custom ID such as GMT-8:00.
    Examples -
    • SIMPLE_DATE_FORMAT (only in master branch)
    • SIMPLE_DATE_FORMAT|yyyy-MM-dd HH:mm:ss
    • SIMPLE_DATE_FORMAT|yyyy-MM-dd|IST

{% hint style="warning" %} Only datetime timeformats in lexicographical order are support in Pinot. so yyyy-MM-dd ,MM-dd and yyyy-dd are valid while MM-dd-yyyy is not.
The order is decided as year > month > day > hour > minutes > second. {% endhint %}

Old date time formats

These date-time formats are still supported in Pinot for backward compatibility. However, new users should prefer to use the formats mentioned in the previous sections.

You will need to provide the format of the date along with the data type in the schema. The format is described using the following syntax: 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. e.g. 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 Joda's DateTimeFormat 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 the 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. Mon Aug 24 12:36:50 America/Los_Angeles 2019

Built-in virtual columns

There are several built-in virtual columns inside the schema the can be used for debugging purposes:

Column Name Column Type Data Type Description
$hostName Dimension STRING Name of the server hosting the data
$segmentName Dimension STRING Name of the segment containing the record
$docId Dimension INT Document id of the record within the segment

These virtual columns can be used in queries in a similar way to regular columns.

Advanced fields

Apart from these, there's some advanced fields. These are common to all field specs.

Property Description
maxLength Max length of this column
virtualColumnProvider Column value provider