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JSON Format

Feldera can ingest and output data in the JSON format

  • via /ingress and /egress REST endpoints, or
  • as a payload received from or sent to a connector

Here we document the JSON format supported by Feldera. The specification consists of four parts:

  1. Encoding invividual table rows. Describes JSON encoding of an individual row in a SQL table or view, e.g.:
    {"part": 1, "vendor": 2, "price": 10000}
  2. Encoding data change events. A data change event represents an insertion, deletion, or modification of a single row, e.g.:
    {"insert": {"part": 1, "vendor": 2, "price": 30000}}
  3. Encoding multiple changes. Describes JSON encoding of a stream of data change events, e.g.:
    {"delete": {"part": 1, "vendor": 2, "price": 10000}}
    {"insert": {"part": 1, "vendor": 2, "price": 30000}}
    {"insert": {"part": 2, "vendor": 3, "price": 34000}}
  4. Configuring JSON event streams. Describes how the user can specify the JSON format for a stream of events when sending and receiving data via connectors or over HTTP.

Encoding individual rows

A row in a SQL table or view is encoded as a JSON object whose keys match the names of the columns in the table. Keys can occur in an arbitrary order. Column names are case-insensitive, except for columns whose names are declared in double quotes (e.g., create table foo("col")). NULLs are encoded as JSON null values or by simply omitting the columns whose value is NULL.

For example, given the following table declaration

create table json_test (
b BOOLEAN,
i INTEGER,
d DOUBLE,
v VARCHAR(32),
cc CHAR(16),
t TIME,
ts TIMESTAMP,
dt DATE,
ar BIGINT ARRAY
);

the JSON encoding of a row would look like this:

{
"B":true,
"I":-1625240816,
"D":0.7879946935782574,
"V":"quod",
"CC":"voluptatem",
"T":"05:05:24",
"TS":"2023-11-21 23:19:09",
"DT":"2495-03-07",
"AR":[1,2,3,4,5]
}

Types

TypeExample
BOOLEANtrue, false
TINYINT,SMALLINT, INTEGER, BIGINT1, -9
FLOAT, DOUBLE, DECIMAL-1.40, "-1.40", 12.53, "12.53", 1e20, "1e20"
VARCHAR, CHAR, STRINGabc
TIME12:12:33, 23:59:29.483, 23:59:09.483221092
TIMESTAMP2024-02-25 12:12:33
DATE2024-02-25
BIGINT ARRAY[1, 2]
VARCHAR ARRAY ARRAY[[ 'abc', '123'], ['c', 'sql']]

BOOLEAN

The accepted values are true or false.

Integers (TINYINT, SMALLINT, INTEGER, BIGINT)

Must be a valid integer and fit the range of the type (see SQL Types), otherwise an error is returned on ingress.

Decimals (DECIMAL / NUMERIC)

Both the scientific notation (e.g., 3e234) and standard floating point numbers (1.23) are valid. The parser will accept decimals formatted as JSON numbers (1.234) or strings ("1.234"). The latter representation is more robust as it avoids loss of precision during parsing (the Rust JSON parser we use represents all fractional numbers as 64-bit floating point numbers internally, which can cause loss of precision for decimal numbers that cannot be accurately represented in that way).

Floating point numbers (FLOAT, DOUBLE)

Both the scientific notation (e.g., 3e234) and standard floating point numbers (1.23) are valid.

note

NaN, Inf, and -Inf floating point values are currently not supported by the JSON parser and encoder.

Strings (CHAR, VARCHAR, STRING, TEXT)

SQL strings are encoded as JSON strings.

note

The JSON parser does not currently enforce limits on the number of characters in a string. Strings that exceed the length specified in the SQL table declaration are ingested without truncation.

TIME

Specifies times using the HH:MM:SS.fffffffff format where:

  • HH is hours from 00-23.
  • MM is minutes from 00-59.
  • SS is seconds from 00-59.
  • fffffffff is the sub-second precision up to 9 digits from 0 to 999999999

A leading 0 can be skipped in hours, minutes and seconds. Specifying the subsecond precision is optional and can have any number of digits from 0 to 9. Leading and trailing whitespaces are ignored.

DATE

Specifies dates using the YYYY-MM-DD format.

  • YYYY is the year from 0001-9999
  • MM is the month from 01-12
  • DD is the day from 01-31

Invalid dates (e.g., 1997-02-29) are rejected with an error during ingress. Leading zeros are skipped, e.g., 0001-1-01, 1-1-1, 0000-1-1 are all equal and valid. Leading and trailing whitespaces are ignored.

TIMESTAMP

Specifies dates using the YYYY-MM-DD HH:MM:SS.fff format.

  • YYYY is the year from 0001-9999
  • MM is the month from 01-12
  • DD is the day from 01-31
  • HH is hours from 00-23.
  • MM is minutes from 00-59.
  • SS is seconds from 00-59.
  • fff is the sub-second precision up to 3 digits from 0 to 999

Note that the same rules as specified in the Date and Time sections apply, except that the sub-second precision is limited to three digits (microseconds). Specifying more digits for the subsecond precision on ingress will trim the fraction to microseconds. Leading and trailing whitespaces are ignored.

ARRAY

Arrays are encoded as JSON arrays.

Encoding data change events

Feldera operates over streams of data change events. A data change event represents an insertion, deletion, or modification of a single row in a SQL table or view. We currently support two data change event formats in JSON: (1) the raw format and (2) the insert/delete format.

The insert/delete format

A data change event in this format is represented as a JSON object with a single key, which must be equal to insert or delete. The associated value represents the table row to be inserted or deleted, encoded using the format documented above. Example row insertion event:

{"insert": {"part": 1, "vendor": 2, "price": 30000}}

Example row deletion event:

{"delete": {"part": 1, "vendor": 2, "price": 10000}}

The raw format

This format is applicable to append-only event streams where rows can only be inserted but not deleted. In this case, a data change event can be represented as a SQL record without any additional framing, with the insert operation being implied, e.g., the following data change event in the raw format

{"part": 1, "vendor": 2, "price": 30000}

is equivalent to

{"insert": {"part": 1, "vendor": 2, "price": 30000}}

Encoding multiple changes

Data change events are exchanged as data streams transmitted over transports such as HTTP or Kafka. We use newline-delimited JSON (NDJSON) to assemble individual data change events into a stream. In NDJSON, each line within the data stream represents a self-contained and valid JSON document, in this case, a data change event:

{"delete": {"part": 1, "vendor": 2, "price": 10000}}
{"insert": {"part": 1, "vendor": 2, "price": 30000}}
{"insert": {"part": 2, "vendor": 3, "price": 34000}}
...

A stream of data change events can be configured to combine multiple events into JSON arrays. This format still uses NDJSON, where each line contains an array of data change events:

[{"delete": {"part": 1, "vendor": 2, "price": 10000}}, {"insert": {"part": 1, "vendor": 2, "price": 30000}}]
[{"insert": {"part": 2, "vendor": 3, "price": 34000}}, {"delete": {"part": 3, "vendor": 1, "price": 5000}}]
...

This format allows one to break up the event stream into transport messages so that each message contains a valid JSON document by encoding all events in the message as an array.

Configuring JSON event streams

Configure connectors via the Feldera Web Console

When creating a new input or output connector using the Feldera Web Console, the data format is configured in the FORMAT section of the connector creation wizard:

  1. choose JSON from the list of supported formats
  2. choose appropriate data change event encoding (Raw or Insert & Delete)
  3. enable array encapsulation if the stream contains events grouped in arrays

Data change event format selector

See also the input/output connector tutorial.

Configure connectors via the REST API

When creating or modifying connectors via the REST API /connectors endpoint, the data format is specified in the format field of the connector configuration:

{
"transport": {
"name": "url",
"config": {
"path":"https://feldera-basics-tutorial.s3.amazonaws.com/part.json"
}
},
"format": {
// Choose JSON format for the connector.
"name": "json",

"config": {
// Choose data change event format for this connector.
// Supported values are `insert_delete` and `raw`.
"update_format": "insert_delete",

// Disable array encoding.
"array": false
}
},
"max_buffered_records":1000000
}

Streaming JSON over HTTP

When sending data to a pipeline over HTTP via the /ingress API endpoint, the data format is specified as part of the URL, e.g.:

# `?format=json` - Chooses JSON format for the stream.
# `&update_format=insert_delete` - Specifies data change event format. Supported values are `insert_delete` and `raw`.
# `&array=false` - Don't use array encoding.
curl -X 'POST' 'http://localhost:8080/v0/pipelines/018a67a5-32e8-7e23-825d-a8a64872ab7c/ingress/PART?format=json&update_format=insert_delete&array=false' -d '
{"insert": {"id": 1, "name": "Flux Capacitor"}}
{"insert": {"id": 2, "name": "Warp Core"}}
{"insert": {"id": 3, "name": "Kyber Crystal"}}'

When receiving data from a pipeline over HTTP via the /egress API endpoint, we currently only support the insert/delete data change event format with array encapsulation. Specify ?format=json in the URL to choose this encoding for output data.

curl -s -N -X 'POST' http://localhost:8080/v0/pipelines/018a67a5-32e8-7e23-825d-a8a64872ab7c/egress/PREFERRED_VENDOR?format=json

See also the HTTP input and output tutorial.