Connect to External Systems

Flink’s Table API & SQL programs can be connected to other external systems for reading and writing both batch and streaming tables. A table source provides access to data which is stored in external systems (such as a database, key-value store, message queue, or file system). A table sink emits a table to an external storage system. Depending on the type of source and sink, they support different formats such as CSV, Parquet, or ORC.

This page describes how to declare built-in table sources and/or table sinks and register them in Flink. After a source or sink has been registered, it can be accessed by Table API & SQL statements.

Attention If you want to implement your own custom table source or sink, have a look at the user-defined sources & sinks page.

Dependencies

The following tables list all available connectors and formats. Their mutual compatibility is tagged in the corresponding sections for table connectors and table formats. The following tables provide dependency information for both projects using a build automation tool (such as Maven or SBT) and SQL Client with SQL JAR bundles.

Connectors

Formats

Overview

Beginning from Flink 1.6, the declaration of a connection to an external system is separated from the actual implementation.

Connections can be specified either

• programmatically using a Descriptor under org.apache.flink.table.descriptors for Table & SQL API
• or declaratively via YAML configuration files for the SQL Client.This allows not only for better unification of APIs and SQL Client but also for better extensibility in case of custom implementations without changing the actual declaration.

Every declaration is similar to a SQL CREATE TABLE statement. One can define the name of the table, the schema of the table, a connector, and a data format upfront for connecting to an external system.

The connector describes the external system that stores the data of a table. Storage systems such as Apacha Kafka or a regular file system can be declared here. The connector might already provide a fixed format with fields and schema.

Some systems support different data formats. For example, a table that is stored in Kafka or in files can encode its rows with CSV, JSON, or Avro. A database connector might need the table schema here. Whether or not a storage system requires the definition of a format, is documented for every connector. Different systems also require different types of formats (e.g., column-oriented formats vs. row-oriented formats). The documentation states which format types and connectors are compatible.

The table schema defines the schema of a table that is exposed to SQL queries. It describes how a source maps the data format to the table schema and a sink vice versa. The schema has access to fields defined by the connector or format. It can use one or more fields for extracting or inserting time attributes. If input fields have no deterministic field order, the schema clearly defines column names, their order, and origin.

The subsequent sections will cover each definition part (connector, format, and schema) in more detail. The following example shows how to pass them:

tableEnvironment
  .connect(...)
  .withFormat(...)
  .withSchema(...)
  .inAppendMode()
  .registerTableSource("MyTable")

table_environment \
    .connect(...) \
    .with_format(...) \
    .with_schema(...) \
    .in_append_mode() \
    .register_table_source("MyTable")

name: MyTable
type: source
update-mode: append
connector: ...
format: ...
schema: ...

tableEnvironment.sqlUpdate("CREATE TABLE MyTable (...) WITH (...)")

The table’s type (source, sink, or both) determines how a table is registered. In case of table type both, both a table source and table sink are registered under the same name. Logically, this means that we can both read and write to such a table similarly to a table in a regular DBMS.

For streaming queries, an update mode declares how to communicate between a dynamic table and the storage system for continuous queries.

The following code shows a full example of how to connect to Kafka for reading Avro records.

tableEnvironment
  // declare the external system to connect to
  .connect(
    new Kafka()
      .version("0.10")
      .topic("test-input")
      .startFromEarliest()
      .property("zookeeper.connect", "localhost:2181")
      .property("bootstrap.servers", "localhost:9092")
  )
  // declare a format for this system
  .withFormat(
    new Avro()
      .avroSchema(
        "{" +
        "  \"namespace\": \"org.myorganization\"," +
        "  \"type\": \"record\"," +
        "  \"name\": \"UserMessage\"," +
        "    \"fields\": [" +
        "      {\"name\": \"timestamp\", \"type\": \"string\"}," +
        "      {\"name\": \"user\", \"type\": \"long\"}," +
        "      {\"name\": \"message\", \"type\": [\"string\", \"null\"]}" +
        "    ]" +
        "}"
      )
  )
  // declare the schema of the table
  .withSchema(
    new Schema()
      .field("rowtime", Types.SQL_TIMESTAMP)
        .rowtime(new Rowtime()
          .timestampsFromField("timestamp")
          .watermarksPeriodicBounded(60000)
        )
      .field("user", Types.LONG)
      .field("message", Types.STRING)
  )
  // specify the update-mode for streaming tables
  .inAppendMode()
  // register as source, sink, or both and under a name
  .registerTableSource("MyUserTable");

table_environment \
    .connect(  # declare the external system to connect to
        Kafka()
        .version("0.10")
        .topic("test-input")
        .start_from_earliest()
        .property("zookeeper.connect", "localhost:2181")
        .property("bootstrap.servers", "localhost:9092")
    ) \
    .with_format(  # declare a format for this system
        Avro()
        .avro_schema(
            "{"
            "  \"namespace\": \"org.myorganization\","
            "  \"type\": \"record\","
            "  \"name\": \"UserMessage\","
            "    \"fields\": ["
            "      {\"name\": \"timestamp\", \"type\": \"string\"},"
            "      {\"name\": \"user\", \"type\": \"long\"},"
            "      {\"name\": \"message\", \"type\": [\"string\", \"null\"]}"
            "    ]"
            "}"
        )
    ) \
    .with_schema(  # declare the schema of the table
        Schema()
        .field("rowtime", DataTypes.TIMESTAMP())
        .rowtime(
            Rowtime()
            .timestamps_from_field("timestamp")
            .watermarks_periodic_bounded(60000)
        )
        .field("user", DataTypes.BIGINT())
        .field("message", DataTypes.STRING())
    ) \
    .in_append_mode() \
    .register_table_source("MyUserTable")  
    # specify the update-mode for streaming tables and
    # register as source, sink, or both and under a name

tables:
  - name: MyUserTable      # name the new table
    type: source           # declare if the table should be "source", "sink", or "both"
    update-mode: append    # specify the update-mode for streaming tables
    # declare the external system to connect to
    connector:
      type: kafka
      version: "0.10"
      topic: test-input
      startup-mode: earliest-offset
      properties:
        - key: zookeeper.connect
          value: localhost:2181
        - key: bootstrap.servers
          value: localhost:9092
    # declare a format for this system
    format:
      type: avro
      avro-schema: >
        {
          "namespace": "org.myorganization",
          "type": "record",
          "name": "UserMessage",
            "fields": [
              {"name": "ts", "type": "string"},
              {"name": "user", "type": "long"},
              {"name": "message", "type": ["string", "null"]}
            ]
        }
    # declare the schema of the table
    schema:
      - name: rowtime
        type: TIMESTAMP
        rowtime:
          timestamps:
            type: from-field
            from: ts
          watermarks:
            type: periodic-bounded
            delay: "60000"
      - name: user
        type: BIGINT
      - name: message
        type: VARCHAR

CREATE TABLE MyUserTable (
  `user` BIGINT,
  message VARCHAR,
  ts VARCHAR
) WITH (
  -- declare the external system to connect to
  'connector.type' = 'kafka',
  'connector.version' = '0.10',
  'connector.topic' = 'topic_name',
  'connector.startup-mode' = 'earliest-offset',
  'connector.properties.0.key' = 'zookeeper.connect',
  'connector.properties.0.value' = 'localhost:2181',
  'connector.properties.1.key' = 'bootstrap.servers',
  'connector.properties.1.value' = 'localhost:9092',
  'update-mode' = 'append',
  -- declare a format for this system
  'format.type' = 'avro',
  'format.avro-schema' = '{
                            "namespace": "org.myorganization",
                            "type": "record",
                            "name": "UserMessage",
                            "fields": [
                                {"name": "ts", "type": "string"},
                                {"name": "user", "type": "long"},
                                {"name": "message", "type": ["string", "null"]}
                            ]
                         }'
)

In both ways the desired connection properties are converted into normalized, string-based key-value pairs. So-called table factories create configured table sources, table sinks, and corresponding formats from the key-value pairs. All table factories that can be found via Java’s Service Provider Interfaces (SPI) are taken into account when searching for exactly-one matching table factory.

If no factory can be found or multiple factories match for the given properties, an exception will be thrown with additional information about considered factories and supported properties.

Table Schema

The table schema defines the names and types of columns similar to the column definitions of a SQL CREATE TABLE statement. In addition, one can specify how columns are mapped from and to fields of the format in which the table data is encoded. The origin of a field might be important if the name of the column should differ from the input/output format. For instance, a column user_name should reference the field $$-user-name from a JSON format. Additionally, the schema is needed to map types from an external system to Flink’s representation. In case of a table sink, it ensures that only data with valid schema is written to an external system.

The following example shows a simple schema without time attributes and one-to-one field mapping of input/output to table columns.

.withSchema(
  new Schema()
    .field("MyField1", Types.INT)     // required: specify the fields of the table (in this order)
    .field("MyField2", Types.STRING)
    .field("MyField3", Types.BOOLEAN)
)

.with_schema(
    Schema()
    .field("MyField1", DataTypes.INT())  # required: specify the fields of the table (in this order)
    .field("MyField2", DataTypes.STRING())
    .field("MyField3", DataTypes.BOOLEAN())
)

schema:
  - name: MyField1    # required: specify the fields of the table (in this order)
    type: INT
  - name: MyField2
    type: VARCHAR
  - name: MyField3
    type: BOOLEAN

For each field, the following properties can be declared in addition to the column’s name and type:

.withSchema(
  new Schema()
    .field("MyField1", Types.SQL_TIMESTAMP)
      .proctime()      // optional: declares this field as a processing-time attribute
    .field("MyField2", Types.SQL_TIMESTAMP)
      .rowtime(...)    // optional: declares this field as a event-time attribute
    .field("MyField3", Types.BOOLEAN)
      .from("mf3")     // optional: original field in the input that is referenced/aliased by this field
)

.with_schema(
    Schema()
    .field("MyField1", DataTypes.TIMESTAMP())
    .proctime()  # optional: declares this field as a processing-time attribute
    .field("MyField2", DataTypes.TIMESTAMP())
    .rowtime(...)  # optional: declares this field as a event-time attribute
    .field("MyField3", DataTypes.BOOLEAN())
    .from_origin_field("mf3")  # optional: original field in the input that is referenced/aliased by this field
)

schema:
  - name: MyField1
    type: TIMESTAMP
    proctime: true    # optional: boolean flag whether this field should be a processing-time attribute
  - name: MyField2
    type: TIMESTAMP
    rowtime: ...      # optional: wether this field should be a event-time attribute
  - name: MyField3
    type: BOOLEAN
    from: mf3         # optional: original field in the input that is referenced/aliased by this field

Time attributes are essential when working with unbounded streaming tables. Therefore both processing-time and event-time (also known as “rowtime”) attributes can be defined as part of the schema.

For more information about time handling in Flink and especially event-time, we recommend the general event-time section.

Rowtime Attributes

In order to control the event-time behavior for tables, Flink provides predefined timestamp extractors and watermark strategies.

The following timestamp extractors are supported:

// Converts an existing LONG or SQL_TIMESTAMP field in the input into the rowtime attribute.
.rowtime(
  new Rowtime()
    .timestampsFromField("ts_field")    // required: original field name in the input
)
// Converts the assigned timestamps from a DataStream API record into the rowtime attribute
// and thus preserves the assigned timestamps from the source.
// This requires a source that assigns timestamps (e.g., Kafka 0.10+).
.rowtime(
  new Rowtime()
    .timestampsFromSource()
)
// Sets a custom timestamp extractor to be used for the rowtime attribute.
// The extractor must extend `org.apache.flink.table.sources.tsextractors.TimestampExtractor`.
.rowtime(
  new Rowtime()
    .timestampsFromExtractor(...)
)

# Converts an existing BIGINT or TIMESTAMP field in the input into the rowtime attribute.
.rowtime(
    Rowtime()
    .timestamps_from_field("ts_field")  # required: original field name in the input
)
# Converts the assigned timestamps into the rowtime attribute
# and thus preserves the assigned timestamps from the source.
# This requires a source that assigns timestamps (e.g., Kafka 0.10+).
.rowtime(
    Rowtime()
    .timestamps_from_source()
)
# Sets a custom timestamp extractor to be used for the rowtime attribute.
# The extractor must extend `org.apache.flink.table.sources.tsextractors.TimestampExtractor`.
# Due to python can not accept java object, so it requires a full-qualified class name of the extractor.
.rowtime(
    Rowtime()
    .timestamps_from_extractor(...)
)

# Converts an existing BIGINT or TIMESTAMP field in the input into the rowtime attribute.
rowtime:
  timestamps:
    type: from-field
    from: "ts_field"                 # required: original field name in the input
# Converts the assigned timestamps from a DataStream API record into the rowtime attribute
# and thus preserves the assigned timestamps from the source.
rowtime:
  timestamps:
    type: from-source

The following watermark strategies are supported:

// Sets a watermark strategy for ascending rowtime attributes. Emits a watermark of the maximum
// observed timestamp so far minus 1. Rows that have a timestamp equal to the max timestamp
// are not late.
.rowtime(
  new Rowtime()
    .watermarksPeriodicAscending()
)
// Sets a built-in watermark strategy for rowtime attributes which are out-of-order by a bounded time interval.
// Emits watermarks which are the maximum observed timestamp minus the specified delay.
.rowtime(
  new Rowtime()
    .watermarksPeriodicBounded(2000)    // delay in milliseconds
)
// Sets a built-in watermark strategy which indicates the watermarks should be preserved from the
// underlying DataStream API and thus preserves the assigned watermarks from the source.
.rowtime(
  new Rowtime()
    .watermarksFromSource()
)

# Sets a watermark strategy for ascending rowtime attributes. Emits a watermark of the maximum
# observed timestamp so far minus 1. Rows that have a timestamp equal to the max timestamp
# are not late.
.rowtime(
    Rowtime()
    .watermarks_periodic_ascending()
)
# Sets a built-in watermark strategy for rowtime attributes which are out-of-order by a bounded time interval.
# Emits watermarks which are the maximum observed timestamp minus the specified delay.
.rowtime(
    Rowtime()
    .watermarks_periodic_bounded(2000)  # delay in milliseconds
)
# Sets a built-in watermark strategy which indicates the watermarks should be preserved from the
# underlying DataStream API and thus preserves the assigned watermarks from the source.
.rowtime(
    Rowtime()
    .watermarks_from_source()
)

# Sets a watermark strategy for ascending rowtime attributes. Emits a watermark of the maximum
# observed timestamp so far minus 1. Rows that have a timestamp equal to the max timestamp
# are not late.
rowtime:
  watermarks:
    type: periodic-ascending
# Sets a built-in watermark strategy for rowtime attributes which are out-of-order by a bounded time interval.
# Emits watermarks which are the maximum observed timestamp minus the specified delay.
rowtime:
  watermarks:
    type: periodic-bounded
    delay: ...                # required: delay in milliseconds
# Sets a built-in watermark strategy which indicates the watermarks should be preserved from the
# underlying DataStream API and thus preserves the assigned watermarks from the source.
rowtime:
  watermarks:
    type: from-source

Make sure to always declare both timestamps and watermarks. Watermarks are required for triggering time-based operations.

Type Strings

Because type information is only available in a programming language, the following type strings are supported for being defined in a YAML file:

VARCHAR
BOOLEAN
TINYINT
SMALLINT
INT
BIGINT
FLOAT
DOUBLE
DECIMAL
DATE
TIME
TIMESTAMP
MAP<fieldtype, fieldtype>        # generic map; e.g. MAP<VARCHAR, INT> that is mapped to Flink's MapTypeInfo
MULTISET<fieldtype>              # multiset; e.g. MULTISET<VARCHAR> that is mapped to Flink's MultisetTypeInfo
PRIMITIVE_ARRAY<fieldtype>       # primitive array; e.g. PRIMITIVE_ARRAY<INT> that is mapped to Flink's PrimitiveArrayTypeInfo
OBJECT_ARRAY<fieldtype>          # object array; e.g. OBJECT_ARRAY<POJO(org.mycompany.MyPojoClass)> that is mapped to
                                 #   Flink's ObjectArrayTypeInfo
ROW<fieldtype, ...>              # unnamed row; e.g. ROW<VARCHAR, INT> that is mapped to Flink's RowTypeInfo
                                 #   with indexed fields names f0, f1, ...
ROW<fieldname fieldtype, ...>    # named row; e.g., ROW<myField VARCHAR, myOtherField INT> that
                                 #   is mapped to Flink's RowTypeInfo
POJO<class>                      # e.g., POJO<org.mycompany.MyPojoClass> that is mapped to Flink's PojoTypeInfo
ANY<class>                       # e.g., ANY<org.mycompany.MyClass> that is mapped to Flink's GenericTypeInfo
ANY<class, serialized>           # used for type information that is not supported by Flink's Table & SQL API

Update Modes

For streaming queries, it is required to declare how to perform the conversion between a dynamic table and an external connector. The update mode specifies which kind of messages should be exchanged with the external system:

Append Mode: In append mode, a dynamic table and an external connector only exchange INSERT messages.

Retract Mode: In retract mode, a dynamic table and an external connector exchange ADD and RETRACT messages. An INSERT change is encoded as an ADD message, a DELETE change as a RETRACT message, and an UPDATE change as a RETRACT message for the updated (previous) row and an ADD message for the updating (new) row. In this mode, a key must not be defined as opposed to upsert mode. However, every update consists of two messages which is less efficient.

Upsert Mode: In upsert mode, a dynamic table and an external connector exchange UPSERT and DELETE messages. This mode requires a (possibly composite) unique key by which updates can be propagated. The external connector needs to be aware of the unique key attribute in order to apply messages correctly. INSERT and UPDATE changes are encoded as UPSERT messages. DELETE changes as DELETE messages. The main difference to a retract stream is that UPDATE changes are encoded with a single message and are therefore more efficient.

Attention The documentation of each connector states which update modes are supported.

.connect(...)
  .inAppendMode()    // otherwise: inUpsertMode() or inRetractMode()

.connect(...) \
    .in_append_mode()  # otherwise: in_upsert_mode() or in_retract_mode()

tables:
  - name: ...
    update-mode: append    # otherwise: "retract" or "upsert"

CREATE TABLE MyTable (
 ...
) WITH (
 'update-mode' = 'append'  -- otherwise: 'retract' or 'upsert'
)

See also the general streaming concepts documentation for more information.

Table Connectors

Flink provides a set of connectors for connecting to external systems.

Please note that not all connectors are available in both batch and streaming yet. Furthermore, not every streaming connector supports every streaming mode. Therefore, each connector is tagged accordingly. A format tag indicates that the connector requires a certain type of format.

File System Connector

Source: BatchSource: Streaming Append ModeSink: BatchSink: Streaming Append ModeFormat: CSV-only

The file system connector allows for reading and writing from a local or distributed filesystem. A filesystem can be defined as:

.connect(
  new FileSystem()
    .path("file:///path/to/whatever")    // required: path to a file or directory
)

.connect(
    FileSystem()
    .path("file:///path/to/whatever")  # required: path to a file or directory
)

connector:
  type: filesystem
  path: "file:///path/to/whatever"    # required: path to a file or directory

CREATE TABLE MyUserTable (
  ...
) WITH (
  'connector.type' = 'filesystem',               -- required: specify to connector type
  'connector.path' = 'file:///path/to/whatever'  -- required: path to a file or directory
)

The file system connector itself is included in Flink and does not require an additional dependency. A corresponding format needs to be specified for reading and writing rows from and to a file system.

Attention Make sure to include Flink File System specific dependencies.

Attention File system sources and sinks for streaming are only experimental. In the future, we will support actual streaming use cases, i.e., directory monitoring and bucket output.

Kafka Connector

Source: Streaming Append ModeSink: Streaming Append ModeFormat: Serialization SchemaFormat: Deserialization Schema

The Kafka connector allows for reading and writing from and to an Apache Kafka topic. It can be defined as follows:

.connect(
  new Kafka()
    .version("0.11")    // required: valid connector versions are
                        //   "0.8", "0.9", "0.10", "0.11", and "universal"
    .topic("...")       // required: topic name from which the table is read
    // optional: connector specific properties
    .property("zookeeper.connect", "localhost:2181")
    .property("bootstrap.servers", "localhost:9092")
    .property("group.id", "testGroup")
    // optional: select a startup mode for Kafka offsets
    .startFromEarliest()
    .startFromLatest()
    .startFromSpecificOffsets(...)
    // optional: output partitioning from Flink's partitions into Kafka's partitions
    .sinkPartitionerFixed()         // each Flink partition ends up in at-most one Kafka partition (default)
    .sinkPartitionerRoundRobin()    // a Flink partition is distributed to Kafka partitions round-robin
    .sinkPartitionerCustom(MyCustom.class)    // use a custom FlinkKafkaPartitioner subclass
)

.connect(
    Kafka()
    .version("0.11")  # required: valid connector versions are
                      # "0.8", "0.9", "0.10", "0.11", and "universal"
    .topic("...")     # required: topic name from which the table is read
    # optional: connector specific properties
    .property("zookeeper.connect", "localhost:2181")
    .property("bootstrap.servers", "localhost:9092")
    .property("group.id", "testGroup")
    # optional: select a startup mode for Kafka offsets
    .start_from_earliest()
    .start_from_latest()
    .start_from_specific_offsets(...)
    # optional: output partitioning from Flink's partitions into Kafka's partitions
    .sink_partitioner_fixed()        # each Flink partition ends up in at-most one Kafka partition (default)
    .sink_partitioner_round_robin()  # a Flink partition is distributed to Kafka partitions round-robin
    .sink_partitioner_custom("full.qualified.custom.class.name")  # use a custom FlinkKafkaPartitioner subclass
)

connector:
  type: kafka
  version: "0.11"     # required: valid connector versions are
                      #   "0.8", "0.9", "0.10", "0.11", and "universal"
  topic: ...          # required: topic name from which the table is read
  properties:         # optional: connector specific properties
    - key: zookeeper.connect
      value: localhost:2181
    - key: bootstrap.servers
      value: localhost:9092
    - key: group.id
      value: testGroup
  startup-mode: ...   # optional: valid modes are "earliest-offset", "latest-offset",
                      # "group-offsets", or "specific-offsets"
  specific-offsets:   # optional: used in case of startup mode with specific offsets
    - partition: 0
      offset: 42
    - partition: 1
      offset: 300
  sink-partitioner: ...    # optional: output partitioning from Flink's partitions into Kafka's partitions
                           # valid are "fixed" (each Flink partition ends up in at most one Kafka partition),
                           # "round-robin" (a Flink partition is distributed to Kafka partitions round-robin)
                           # "custom" (use a custom FlinkKafkaPartitioner subclass)
  sink-partitioner-class: org.mycompany.MyPartitioner  # optional: used in case of sink partitioner custom

CREATE TABLE MyUserTable (
  ...
) WITH (
  'connector.type' = 'kafka',       
  'connector.version' = '0.11',     -- required: valid connector versions are
                                    -- "0.8", "0.9", "0.10", "0.11", and "universal"
  'connector.topic' = 'topic_name', -- required: topic name from which the table is read
  'update-mode' = 'append',         -- required: update mode when used as table sink, 
                                    -- only support append mode now.
  'connector.properties.0.key' = 'zookeeper.connect', -- optional: connector specific properties
  'connector.properties.0.value' = 'localhost:2181',
  'connector.properties.1.key' = 'bootstrap.servers',
  'connector.properties.1.value' = 'localhost:9092',
  'connector.properties.2.key' = 'group.id',
  'connector.properties.2.value' = 'testGroup',
  'connector.startup-mode' = 'earliest-offset',    -- optional: valid modes are "earliest-offset", 
                                                   -- "latest-offset", "group-offsets", 
                                                   -- or "specific-offsets"
  -- optional: used in case of startup mode with specific offsets
  'connector.specific-offsets.0.partition' = '0',
  'connector.specific-offsets.0.offset' = '42',
  'connector.specific-offsets.1.partition' = '1',
  'connector.specific-offsets.1.offset' = '300',
  'connector.sink-partitioner' = '...',  -- optional: output partitioning from Flink's partitions 
                                         -- into Kafka's partitions valid are "fixed" 
                                         -- (each Flink partition ends up in at most one Kafka partition),
                                         -- "round-robin" (a Flink partition is distributed to 
                                         -- Kafka partitions round-robin)
                                         -- "custom" (use a custom FlinkKafkaPartitioner subclass)
  -- optional: used in case of sink partitioner custom
  'connector.sink-partitioner-class' = 'org.mycompany.MyPartitioner'
)

Specify the start reading position: By default, the Kafka source will start reading data from the committed group offsets in Zookeeper or Kafka brokers. You can specify other start positions, which correspond to the configurations in section Kafka Consumers Start Position Configuration.

Flink-Kafka Sink Partitioning: By default, a Kafka sink writes to at most as many partitions as its own parallelism (each parallel instance of the sink writes to exactly one partition). In order to distribute the writes to more partitions or control the routing of rows into partitions, a custom sink partitioner can be provided. The round-robin partitioner is useful to avoid an unbalanced partitioning. However, it will cause a lot of network connections between all the Flink instances and all the Kafka brokers.

Consistency guarantees: By default, a Kafka sink ingests data with at-least-once guarantees into a Kafka topic if the query is executed with checkpointing enabled.

Kafka 0.10+ Timestamps: Since Kafka 0.10, Kafka messages have a timestamp as metadata that specifies when the record was written into the Kafka topic. These timestamps can be used for a rowtime attribute by selecting timestamps: from-source in YAML and timestampsFromSource() in Java/Scala respectively.

Kafka 0.11+ Versioning: Since Flink 1.7, the Kafka connector definition should be independent of a hard-coded Kafka version. Use the connector version universal as a wildcard for Flink’s Kafka connector that is compatible with all Kafka versions starting from 0.11.

Make sure to add the version-specific Kafka dependency. In addition, a corresponding format needs to be specified for reading and writing rows from and to Kafka.

Elasticsearch Connector

Sink: Streaming Append ModeSink: Streaming Upsert ModeFormat: JSON-only

The Elasticsearch connector allows for writing into an index of the Elasticsearch search engine.

The connector can operate in upsert mode for exchanging UPSERT/DELETE messages with the external system using a key defined by the query.

For append-only queries, the connector can also operate in append mode for exchanging only INSERT messages with the external system. If no key is defined by the query, a key is automatically generated by Elasticsearch.

The connector can be defined as follows:

.connect(
  new Elasticsearch()
    .version("6")                      // required: valid connector versions are "6"
    .host("localhost", 9200, "http")   // required: one or more Elasticsearch hosts to connect to
    .index("MyUsers")                  // required: Elasticsearch index
    .documentType("user")              // required: Elasticsearch document type
    .keyDelimiter("$")        // optional: delimiter for composite keys ("_" by default)
                              //   e.g., "$" would result in IDs "KEY1$KEY2$KEY3"
    .keyNullLiteral("n/a")    // optional: representation for null fields in keys ("null" by default)
    // optional: failure handling strategy in case a request to Elasticsearch fails (fail by default)
    .failureHandlerFail()          // optional: throws an exception if a request fails and causes a job failure
    .failureHandlerIgnore()        //   or ignores failures and drops the request
    .failureHandlerRetryRejected() //   or re-adds requests that have failed due to queue capacity saturation
    .failureHandlerCustom(...)     //   or custom failure handling with a ActionRequestFailureHandler subclass
    // optional: configure how to buffer elements before sending them in bulk to the cluster for efficiency
    .disableFlushOnCheckpoint()    // optional: disables flushing on checkpoint (see notes below!)
    .bulkFlushMaxActions(42)       // optional: maximum number of actions to buffer for each bulk request
    .bulkFlushMaxSize("42 mb")     // optional: maximum size of buffered actions in bytes per bulk request
                                   //   (only MB granularity is supported)
    .bulkFlushInterval(60000L)     // optional: bulk flush interval (in milliseconds)
    .bulkFlushBackoffConstant()    // optional: use a constant backoff type
    .bulkFlushBackoffExponential() //   or use an exponential backoff type
    .bulkFlushBackoffMaxRetries(3) // optional: maximum number of retries
    .bulkFlushBackoffDelay(30000L) // optional: delay between each backoff attempt (in milliseconds)
    // optional: connection properties to be used during REST communication to Elasticsearch
    .connectionMaxRetryTimeout(3)  // optional: maximum timeout (in milliseconds) between retries
    .connectionPathPrefix("/v1")   // optional: prefix string to be added to every REST communication
)

.connect(
    Elasticsearch()
    .version("6")                      # required: valid connector versions are "6"
    .host("localhost", 9200, "http")   # required: one or more Elasticsearch hosts to connect to
    .index("MyUsers")                  # required: Elasticsearch index
    .document_type("user")             # required: Elasticsearch document type
    .key_delimiter("$")       # optional: delimiter for composite keys ("_" by default)
                              #   e.g., "$" would result in IDs "KEY1$KEY2$KEY3"
    .key_null_literal("n/a")  # optional: representation for null fields in keys ("null" by default)
    # optional: failure handling strategy in case a request to Elasticsearch fails (fail by default)
    .failure_handler_fail()             # optional: throws an exception if a request fails and causes a job failure
    .failure_handler_ignore()           #   or ignores failures and drops the request
    .failure_handler_retry_rejected()   #   or re-adds requests that have failed due to queue capacity saturation
    .failure_handler_custom(...)        #   or custom failure handling with a ActionRequestFailureHandler subclass
    # optional: configure how to buffer elements before sending them in bulk to the cluster for efficiency
    .disable_flush_on_checkpoint()      # optional: disables flushing on checkpoint (see notes below!)
    .bulk_flush_max_actions(42)         # optional: maximum number of actions to buffer for each bulk request
    .bulk_flush_max_size("42 mb")       # optional: maximum size of buffered actions in bytes per bulk request
                                        #   (only MB granularity is supported)
    .bulk_flush_interval(60000)         # optional: bulk flush interval (in milliseconds)
    .bulk_flush_backoff_constant()      # optional: use a constant backoff type
    .bulk_flush_backoff_exponential()   #   or use an exponential backoff type
    .bulk_flush_backoff_max_retries(3)  # optional: maximum number of retries
    .bulk_flush_backoff_delay(30000)    # optional: delay between each backoff attempt (in milliseconds)
    # optional: connection properties to be used during REST communication to Elasticsearch
    .connection_max_retry_timeout(3)    # optional: maximum timeout (in milliseconds) between retries
    .connection_path_prefix("/v1")      # optional: prefix string to be added to every REST communication
)

connector:
  type: elasticsearch
  version: 6                # required: valid connector versions are "6"
    hosts:                  # required: one or more Elasticsearch hosts to connect to
      - hostname: "localhost"
        port: 9200
        protocol: "http"
    index: "MyUsers"        # required: Elasticsearch index
    document-type: "user"   # required: Elasticsearch document type
    key-delimiter: "$"      # optional: delimiter for composite keys ("_" by default)
                            #   e.g., "$" would result in IDs "KEY1$KEY2$KEY3"
    key-null-literal: "n/a" # optional: representation for null fields in keys ("null" by default)
    # optional: failure handling strategy in case a request to Elasticsearch fails ("fail" by default)
    failure-handler: ...    # valid strategies are "fail" (throws an exception if a request fails and
                            #   thus causes a job failure), "ignore" (ignores failures and drops the request),
                            #   "retry-rejected" (re-adds requests that have failed due to queue capacity
                            #   saturation), or "custom" for failure handling with a
                            #   ActionRequestFailureHandler subclass
    # optional: configure how to buffer elements before sending them in bulk to the cluster for efficiency
    flush-on-checkpoint: true   # optional: disables flushing on checkpoint (see notes below!) ("true" by default)
    bulk-flush:
      max-actions: 42           # optional: maximum number of actions to buffer for each bulk request
      max-size: 42 mb           # optional: maximum size of buffered actions in bytes per bulk request
                                #   (only MB granularity is supported)
      interval: 60000           # optional: bulk flush interval (in milliseconds)
      back-off:                 # optional: backoff strategy ("disabled" by default)
        type: ...               #   valid strategies are "disabled", "constant", or "exponential"
        max-retries: 3          # optional: maximum number of retries
        delay: 30000            # optional: delay between each backoff attempt (in milliseconds)
    # optional: connection properties to be used during REST communication to Elasticsearch
    connection-max-retry-timeout: 3   # optional: maximum timeout (in milliseconds) between retries
    connection-path-prefix: "/v1"     # optional: prefix string to be added to every REST communication

CREATE TABLE MyUserTable (
  ...
) WITH (
  'connector.type' = 'elasticsearch', -- required: specify this table type is elasticsearch
  'connector.version' = '6',          -- required: valid connector versions are "6"
  'connector.hosts.0.hostname' = 'host_name',  -- required: one or more Elasticsearch hosts to connect to
  'connector.hosts.0.port' = '9092',
  'connector.hosts.0.protocol' = 'http',
  'connector.index' = 'MyUsers',       -- required: Elasticsearch index
  'connector.document-type' = 'user',  -- required: Elasticsearch document type
  'update-mode' = 'append',            -- optional: update mode when used as table sink.           
  'connector.key-delimiter' = '$',     -- optional: delimiter for composite keys ("_" by default)
                                       -- e.g., "$" would result in IDs "KEY1$KEY2$KEY3"
  'connector.key-null-literal' = 'n/a',  -- optional: representation for null fields in keys ("null" by default)
  'connector.failure-handler' = '...',   -- optional: failure handling strategy in case a request to 
                                         -- Elasticsearch fails ("fail" by default).
                                         -- valid strategies are 
                                         -- "fail" (throws an exception if a request fails and
                                         -- thus causes a job failure), 
                                         -- "ignore" (ignores failures and drops the request),
                                         -- "retry-rejected" (re-adds requests that have failed due 
                                         -- to queue capacity saturation), 
                                         -- or "custom" for failure handling with a
                                         -- ActionRequestFailureHandler subclass
  -- optional: configure how to buffer elements before sending them in bulk to the cluster for efficiency
  'connector.flush-on-checkpoint' = 'true',   -- optional: disables flushing on checkpoint (see notes below!)
                                              -- ("true" by default)
  'connector.bulk-flush.max-actions' = '42',  -- optional: maximum number of actions to buffer 
                                              -- for each bulk request
  'connector.bulk-flush.max-size' = '42 mb',  -- optional: maximum size of buffered actions in bytes
                                              -- per bulk request
                                              -- (only MB granularity is supported)
  'connector.bulk-flush.interval' = '60000',  -- optional: bulk flush interval (in milliseconds)
  'connector.bulk-flush.back-off.type' = '...',       -- optional: backoff strategy ("disabled" by default)
                                                      -- valid strategies are "disabled", "constant",
                                                      -- or "exponential"
  'connector.bulk-flush.back-off.max-retries' = '3',  -- optional: maximum number of retries
  'connector.bulk-flush.back-off.delay' = '30000',    -- optional: delay between each backoff attempt
                                                      -- (in milliseconds)
  -- optional: connection properties to be used during REST communication to Elasticsearch
  'connector.connection-max-retry-timeout' = '3',     -- optional: maximum timeout (in milliseconds)
                                                      -- between retries
  'connector.connection-path-prefix' = '/v1'          -- optional: prefix string to be added to every
                                                      -- REST communication
)

Bulk flushing: For more information about characteristics of the optional flushing parameters see the corresponding low-level documentation.

Disabling flushing on checkpoint: When disabled, a sink will not wait for all pending action requests to be acknowledged by Elasticsearch on checkpoints. Thus, a sink does NOT provide any strong guarantees for at-least-once delivery of action requests.

Key extraction: Flink automatically extracts valid keys from a query. For example, a query SELECT a, b, c FROM t GROUP BY a, b defines a composite key of the fields a and b. The Elasticsearch connector generates a document ID string for every row by concatenating all key fields in the order defined in the query using a key delimiter. A custom representation of null literals for key fields can be defined.

Attention A JSON format defines how to encode documents for the external system, therefore, it must be added as a dependency.

HBase Connector

Source: BatchSink: BatchSink: Streaming Append ModeSink: Streaming Upsert ModeTemporal Join: Sync Mode

The HBase connector allows for reading from and writing to an HBase cluster.

The connector can operate in upsert mode for exchanging UPSERT/DELETE messages with the external system using a key defined by the query.

For append-only queries, the connector can also operate in append mode for exchanging only INSERT messages with the external system.

The connector can be defined as follows:

connector:
  type: hbase
  version: "1.4.3"                 # required: currently only support "1.4.3"
  table-name: "hbase_table_name" # required: HBase table name
  zookeeper:
    quorum: "localhost:2181"     # required: HBase Zookeeper quorum configuration
    znode.parent: "/test"        # optional: the root dir in Zookeeper for HBase cluster.
                                 # The default value is "/hbase".
  write.buffer-flush:
    max-size: "10mb"             # optional: writing option, determines how many size in memory of buffered
                                 # rows to insert per round trip. This can help performance on writing to JDBC
                                 # database. The default value is "2mb".
    max-rows: 1000               # optional: writing option, determines how many rows to insert per round trip.
                                 # This can help performance on writing to JDBC database. No default value,
                                 # i.e. the default flushing is not depends on the number of buffered rows.
    interval: "2s"               # optional: writing option, sets a flush interval flushing buffered requesting
                                 # if the interval passes, in milliseconds. Default value is "0s", which means
                                 # no asynchronous flush thread will be scheduled.

CREATE TABLE MyUserTable (
  hbase_rowkey_name rowkey_type,
  hbase_column_family_name1 ROW<...>,
  hbase_column_family_name2 ROW<...>
) WITH (
  'connector.type' = 'hbase', -- required: specify this table type is hbase
  'connector.version' = '1.4.3',          -- required: valid connector versions are "1.4.3"
  'connector.table-name' = 'hbase_table_name',  -- required: hbase table name
  'connector.zookeeper.quorum' = 'localhost:2181', -- required: HBase Zookeeper quorum configuration
  'connector.zookeeper.znode.parent' = '/test',    -- optional: the root dir in Zookeeper for HBase cluster.
                                                   -- The default value is "/hbase".
  'connector.write.buffer-flush.max-size' = '10mb', -- optional: writing option, determines how many size in memory of buffered
                                                    -- rows to insert per round trip. This can help performance on writing to JDBC
                                                    -- database. The default value is "2mb".
  'connector.write.buffer-flush.max-rows' = '1000', -- optional: writing option, determines how many rows to insert per round trip.
                                                    -- This can help performance on writing to JDBC database. No default value,
                                                    -- i.e. the default flushing is not depends on the number of buffered rows.
  'connector.write.buffer-flush.interval' = '2s',   -- optional: writing option, sets a flush interval flushing buffered requesting
                                                    -- if the interval passes, in milliseconds. Default value is "0s", which means
                                                    -- no asynchronous flush thread will be scheduled.
)

Columns: All the column families in HBase table must be declared as ROW type, the field name maps to the column family name, and the nested field names map to the column qualifier names. There is no need to declare all the families and qualifiers in the schema, users can declare what’s necessary. Except the ROW type fields, the only one field of atomic type (e.g. STRING, BIGINT) will be recognized as row key of the table. There’s no constraints on the name of row key field.

Temporary join: Lookup join against HBase do not use any caching; data is always queired directly through the HBase client.

Java/Scala/Python API: Java/Scala/Python APIs are not supported yet.

JDBC Connector

Source: BatchSink: BatchSink: Streaming Append ModeSink: Streaming Upsert ModeTemporal Join: Sync Mode

The JDBC connector allows for reading from and writing into an JDBC client.

The connector can operate in upsert mode for exchanging UPSERT/DELETE messages with the external system using a key defined by the query.

For append-only queries, the connector can also operate in append mode for exchanging only INSERT messages with the external system.

To use JDBC connector, need to choose an actual driver to use. Here are drivers currently supported:

Supported Drivers:

The connector can be defined as follows:

connector:
  type: jdbc
  url: "jdbc:mysql://localhost:3306/flink-test"     # required: JDBC DB url
  table: "jdbc_table_name"        # required: jdbc table name
  driver: "com.mysql.jdbc.Driver" # optional: the class name of the JDBC driver to use to connect to this URL.
                                  # If not set, it will automatically be derived from the URL.
  username: "name"                # optional: jdbc user name and password
  password: "password"
  read: # scan options, optional, used when reading from table
    partition: # These options must all be specified if any of them is specified. In addition, partition.num must be specified. They
               # describe how to partition the table when reading in parallel from multiple tasks. partition.column must be a numeric,
               # date, or timestamp column from the table in question. Notice that lowerBound and upperBound are just used to decide
               # the partition stride, not for filtering the rows in table. So all rows in the table will be partitioned and returned.
               # This option applies only to reading.
      column: "column_name" # optional, name of the column used for partitioning the input.
      num: 50               # optional, the number of partitions.
      lower-bound: 500      # optional, the smallest value of the first partition.
      upper-bound: 1000     # optional, the largest value of the last partition.
    fetch-size: 100         # optional, Gives the reader a hint as to the number of rows that should be fetched
                            # from the database when reading per round trip. If the value specified is zero, then
                            # the hint is ignored. The default value is zero.
  lookup: # lookup options, optional, used in temporary join
    cache:
      max-rows: 5000 # optional, max number of rows of lookup cache, over this value, the oldest rows will
                     # be eliminated. "cache.max-rows" and "cache.ttl" options must all be specified if any
                     # of them is specified. Cache is not enabled as default.
      ttl: "10s"     # optional, the max time to live for each rows in lookup cache, over this time, the oldest rows
                     # will be expired. "cache.max-rows" and "cache.ttl" options must all be specified if any of
                     # them is specified. Cache is not enabled as default.
    max-retries: 3   # optional, max retry times if lookup database failed
  write: # sink options, optional, used when writing into table
      flush:
        max-rows: 5000 # optional, flush max size (includes all append, upsert and delete records), 
                       # over this number of records, will flush data. The default value is "5000".
        interval: "2s" # optional, flush interval mills, over this time, asynchronous threads will flush data.
                       # The default value is "0s", which means no asynchronous flush thread will be scheduled. 
      max-retries: 3   # optional, max retry times if writing records to database failed.

CREATE TABLE MyUserTable (
  ...
) WITH (
  'connector.type' = 'jdbc', -- required: specify this table type is jdbc
  'connector.url' = 'jdbc:mysql://localhost:3306/flink-test', -- required: JDBC DB url
  'connector.table' = 'jdbc_table_name',  -- required: jdbc table name
  'connector.driver' = 'com.mysql.jdbc.Driver', -- optional: the class name of the JDBC driver to use to connect to this URL. 
                                                -- If not set, it will automatically be derived from the URL.
  'connector.username' = 'name', -- optional: jdbc user name and password
  'connector.password' = 'password',
  -- scan options, optional, used when reading from table
  -- These options must all be specified if any of them is specified. In addition, partition.num must be specified. They
  -- describe how to partition the table when reading in parallel from multiple tasks. partition.column must be a numeric,
  -- date, or timestamp column from the table in question. Notice that lowerBound and upperBound are just used to decide
  -- the partition stride, not for filtering the rows in table. So all rows in the table will be partitioned and returned.
  -- This option applies only to reading.
  'connector.read.partition.column' = 'column_name', -- optional, name of the column used for partitioning the input.
  'connector.read.partition.num' = '50', -- optional, the number of partitions.
  'connector.read.partition.lower-bound' = '500', -- optional, the smallest value of the first partition.
  'connector.read.partition.upper-bound' = '1000', -- optional, the largest value of the last partition.
  'connector.read.fetch-size' = '100', -- optional, Gives the reader a hint as to the number of rows that should be fetched
                                       -- from the database when reading per round trip. If the value specified is zero, then
                                       -- the hint is ignored. The default value is zero.
  -- lookup options, optional, used in temporary join
  'connector.lookup.cache.max-rows' = '5000', -- optional, max number of rows of lookup cache, over this value, the oldest rows will
                                              -- be eliminated. "cache.max-rows" and "cache.ttl" options must all be specified if any
                                              -- of them is specified. Cache is not enabled as default.
  'connector.lookup.cache.ttl' = '10s', -- optional, the max time to live for each rows in lookup cache, over this time, the oldest rows
                                        -- will be expired. "cache.max-rows" and "cache.ttl" options must all be specified if any of
                                        -- them is specified. Cache is not enabled as default.
  'connector.lookup.max-retries' = '3', -- optional, max retry times if lookup database failed
  -- sink options, optional, used when writing into table
  'connector.write.flush.max-rows' = '5000', -- optional, flush max size (includes all append, upsert and delete records), 
                                             -- over this number of records, will flush data. The default value is "5000".
  'connector.write.flush.interval' = '2s', -- optional, flush interval mills, over this time, asynchronous threads will flush data.
                                           -- The default value is "0s", which means no asynchronous flush thread will be scheduled. 
  'connector.write.max-retries' = '3' -- optional, max retry times if writing records to database failed
)

Upsert sink: Flink automatically extracts valid keys from a query. For example, a query SELECT a, b, c FROM t GROUP BY a, b defines a composite key of the fields a and b. If a JDBC table is used as upsert sink, please make sure keys of the query is one of the unique key sets or primary key of the underlying database. This can guarantee the output result is as expected.

Temporary Join: JDBC connector can be used in temporal join as a lookup source. Currently, only sync lookup mode is supported. The lookup cache options (connector.lookup.cache.max-rows and connector.lookup.cache.ttl) must all be specified if any of them is specified. The lookup cache is used to improve performance of temporal join JDBC connector by querying the cache first instead of send all requests to remote database. But the returned value might not be the latest if it is from the cache. So it’s a balance between throughput and correctness.

Writing: As default, the connector.write.flush.interval is 0s and connector.write.flush.max-rows is 5000, which means for low traffic queries, the buffered output rows may not be flushed to database for a long time. So the interval configuration is recommended to set.

Table Formats

Flink provides a set of table formats that can be used with table connectors.

A format tag indicates the format type for matching with a connector.

CSV Format

Format: Serialization SchemaFormat: Deserialization Schema

The CSV format aims to comply with RFC-4180 (“Common Format andMIME Type for Comma-Separated Values (CSV) Files”) proposed by the Internet Engineering Task Force (IETF).

The format allows to read and write CSV data that corresponds to a given format schema. The format schema can bedefined either as a Flink type or derived from the desired table schema.

If the format schema is equal to the table schema, the schema can also be automatically derived. This allows fordefining schema information only once. The names, types, and fields’ order of the format are determined by thetable’s schema. Time attributes are ignored if their origin is not a field. A from definition in the tableschema is interpreted as a field renaming in the format.

The CSV format can be used as follows:

.withFormat(
  new Csv()
    // required: define the schema either by using type information
    .schema(Type.ROW(...))
    // or use the table's schema
    .deriveSchema()
    .fieldDelimiter(';')         // optional: field delimiter character (',' by default)
    .lineDelimiter("\r\n")       // optional: line delimiter ("\n" by default;
                                 //   otherwise "\r" or "\r\n" are allowed)
    .quoteCharacter('\'')        // optional: quote character for enclosing field values ('"' by default)
    .allowComments()             // optional: ignores comment lines that start with '#' (disabled by default);
                                 //   if enabled, make sure to also ignore parse errors to allow empty rows
    .ignoreParseErrors()         // optional: skip fields and rows with parse errors instead of failing;
                                 //   fields are set to null in case of errors
    .arrayElementDelimiter("|")  // optional: the array element delimiter string for separating
                                 //   array and row element values (";" by default)
    .escapeCharacter('\\')       // optional: escape character for escaping values (disabled by default)
    .nullLiteral("n/a")          // optional: null literal string that is interpreted as a
                                 //   null value (disabled by default)
)

.with_format(
    Csv()
    # required: define the schema either by using type information
    .schema(DataTypes.ROW(...))
    # or use the table's schema
    .derive_schema()
    .field_delimiter(';')          # optional: field delimiter character (',' by default)
    .line_delimiter("\r\n")        # optional: line delimiter ("\n" by default;
                                   #   otherwise "\r" or "\r\n" are allowed)
    .quote_character('\'')         # optional: quote character for enclosing field values ('"' by default)
    .allow_comments()              # optional: ignores comment lines that start with '#' (disabled by default);
                                   #   if enabled, make sure to also ignore parse errors to allow empty rows
    .ignore_parse_errors()         # optional: skip fields and rows with parse errors instead of failing;
                                   #   fields are set to null in case of errors
    .array_element_delimiter("|")  # optional: the array element delimiter string for separating
                                   #   array and row element values (";" by default)
    .escape_character('\\')        # optional: escape character for escaping values (disabled by default)
    .null_literal("n/a")           # optional: null literal string that is interpreted as a
                                   #   null value (disabled by default)
)

format:
  type: csv
  # required: define the schema either by using type information
  schema: "ROW(lon FLOAT, rideTime TIMESTAMP)"
  # or use the table's schema
  derive-schema: true
  field-delimiter: ";"         # optional: field delimiter character (',' by default)
  line-delimiter: "\r\n"       # optional: line delimiter ("\n" by default; otherwise "\r" or "\r\n" are allowed)
  quote-character: "'"         # optional: quote character for enclosing field values ('"' by default)
  allow-comments: true         # optional: ignores comment lines that start with "#" (disabled by default);
                               #   if enabled, make sure to also ignore parse errors to allow empty rows
  ignore-parse-errors: true    # optional: skip fields and rows with parse errors instead of failing;
                               #   fields are set to null in case of errors
  array-element-delimiter: "|" # optional: the array element delimiter string for separating
                               #   array and row element values (";" by default)
  escape-character: "\\"       # optional: escape character for escaping values (disabled by default)
  null-literal: "n/a"          # optional: null literal string that is interpreted as a
                               #   null value (disabled by default)

CREATE TABLE MyUserTable (
  ...
) WITH (
  'format.type' = 'csv',                  -- required: specify the schema type
  'format.fields.0.name' = 'lon',         -- required: define the schema either by using type information
  'format.fields.0.type' = 'FLOAT',
  'format.fields.1.name' = 'rideTime',
  'format.fields.1.type' = 'TIMESTAMP',
  'format.derive-schema' = 'true',        -- or use the table's schema
  'format.field-delimiter' = ';',         -- optional: field delimiter character (',' by default)
  'format.line-delimiter' = '\r\n',       -- optional: line delimiter ("\n" by default; otherwise
                                          -- "\r" or "\r\n" are allowed)
  'format.quote-character' = '''',        -- optional: quote character for enclosing field values ('"' by default)
  'format.allow-comments' = true,         -- optional: ignores comment lines that start with "#" 
                                          -- (disabled by default);
                                          -- if enabled, make sure to also ignore parse errors to allow empty rows
  'format.ignore-parse-errors' = 'true',  -- optional: skip fields and rows with parse errors instead of failing;
                                          -- fields are set to null in case of errors
  'format.array-element-delimiter' = '|', -- optional: the array element delimiter string for separating
                                          -- array and row element values (";" by default)
  'format.escape-character' = '\\',       -- optional: escape character for escaping values (disabled by default)
  'format.null-literal' = 'n/a'           -- optional: null literal string that is interpreted as a
                                          -- null value (disabled by default)
)

The following table lists supported types that can be read and written:

Numeric types: Value should be a number but the literal "null" can also be understood. An empty string isconsidered null. Values are also trimmed (leading/trailing white space). Numbers are parsed usingJava’s valueOf semantics. Other non-numeric strings may cause a parsing exception.

String and time types: Value is not trimmed. The literal "null" can also be understood. Time typesmust be formatted according to the Java SQL time format with millisecond precision. For example:2018-01-01 for date, 20:43:59 for time, and 2018-01-01 20:43:59.999 for timestamp.

Boolean type: Value is expected to be a boolean ("true", "false") string or "null". Empty strings areinterpreted as false. Values are trimmed (leading/trailing white space). Other values result in an exception.

Nested types: Array and row types are supported for one level of nesting using the array element delimiter.

Primitive byte arrays: Primitive byte arrays are handled in Base64-encoded representation.

Line endings: Line endings need to be considered even for row-based connectors (such as Kafka)to be ignored for unquoted string fields at the end of a row.

Escaping and quoting: The following table shows examples of how escaping and quoting affect the parsingof a string using * for escaping and ' for quoting:

Make sure to add the CSV format as a dependency.

JSON Format

Format: Serialization SchemaFormat: Deserialization Schema

The JSON format allows to read and write JSON data that corresponds to a given format schema. The format schema can be defined either as a Flink type, as a JSON schema, or derived from the desired table schema. A Flink type enables a more SQL-like definition and mapping to the corresponding SQL data types. The JSON schema allows for more complex and nested structures.

If the format schema is equal to the table schema, the schema can also be automatically derived. This allows for defining schema information only once. The names, types, and fields’ order of the format are determined by the table’s schema. Time attributes are ignored if their origin is not a field. A from definition in the table schema is interpreted as a field renaming in the format.

The JSON format can be used as follows:

.withFormat(
  new Json()
    .failOnMissingField(true)   // optional: flag whether to fail if a field is missing or not, false by default
    // required: define the schema either by using type information which parses numbers to corresponding types
    .schema(Type.ROW(...))
    // or by using a JSON schema which parses to DECIMAL and TIMESTAMP
    .jsonSchema(
      "{" +
      "  type: 'object'," +
      "  properties: {" +
      "    lon: {" +
      "      type: 'number'" +
      "    }," +
      "    rideTime: {" +
      "      type: 'string'," +
      "      format: 'date-time'" +
      "    }" +
      "  }" +
      "}"
    )
    // or use the table's schema
    .deriveSchema()
)

.with_format(
    Json()
    .fail_on_missing_field(True)   # optional: flag whether to fail if a field is missing or not, False by default
    # required: define the schema either by using type information which parses numbers to corresponding types
    .schema(DataTypes.ROW(...))
    # or by using a JSON schema which parses to DECIMAL and TIMESTAMP
    .json_schema(
        "{"
        "  type: 'object',"
        "  properties: {"
        "    lon: {"
        "      type: 'number'"
        "    },"
        "    rideTime: {"
        "      type: 'string',"
        "      format: 'date-time'"
        "    }"
        "  }"
        "}"
    )
    # or use the table's schema
    .derive_schema()
)

format:
  type: json
  fail-on-missing-field: true   # optional: flag whether to fail if a field is missing or not, false by default
  # required: define the schema either by using a type string which parses numbers to corresponding types
  schema: "ROW(lon FLOAT, rideTime TIMESTAMP)"
  # or by using a JSON schema which parses to DECIMAL and TIMESTAMP
  json-schema: >
    {
      type: 'object',
      properties: {
        lon: {
          type: 'number'
        },
        rideTime: {
          type: 'string',
          format: 'date-time'
        }
      }
    }
  # or use the table's schema
  derive-schema: true

CREATE TABLE MyUserTable (
  ...
) WITH (
  'format.type' = 'json',                   -- required: specify the format type
  'format.fail-on-missing-field' = 'true'   -- optional: flag whether to fail if a field is missing or not, false by default
  'format.fields.0.name' = 'lon',           -- required: define the schema either by using a type string which parses numbers to corresponding types
  'format.fields.0.type' = 'FLOAT',
  'format.fields.1.name' = 'rideTime',
  'format.fields.1.type' = 'TIMESTAMP',
  'format.json-schema' =                    -- or by using a JSON schema which parses to DECIMAL and TIMESTAMP
    '{
      "type": "object",
      "properties": {
        "lon": {
          "type": "number"
        },
        "rideTime": {
          "type": "string",
          "format": "date-time"
        }
      }
    }',
  'format.derive-schema' = 'true'          -- or use the table's schema
)

The following table shows the mapping of JSON schema types to Flink SQL types:

Currently, Flink supports only a subset of the JSON schema specification draft-07. Union types (as well as allOf, anyOf, not) are not supported yet. oneOf and arrays of types are only supported for specifying nullability.

Simple references that link to a common definition in the document are supported as shown in the more complex example below:

{
  "definitions": {
    "address": {
      "type": "object",
      "properties": {
        "street_address": {
          "type": "string"
        },
        "city": {
          "type": "string"
        },
        "state": {
          "type": "string"
        }
      },
      "required": [
        "street_address",
        "city",
        "state"
      ]
    }
  },
  "type": "object",
  "properties": {
    "billing_address": {
      "$ref": "#/definitions/address"
    },
    "shipping_address": {
      "$ref": "#/definitions/address"
    },
    "optional_address": {
      "oneOf": [
        {
          "type": "null"
        },
        {
          "$ref": "#/definitions/address"
        }
      ]
    }
  }
}

Missing Field Handling: By default, a missing JSON field is set to null. You can enable strict JSON parsing that will cancel the source (and query) if a field is missing.

Make sure to add the JSON format as a dependency.

Apache Avro Format

Format: Serialization SchemaFormat: Deserialization Schema

The Apache Avro format allows to read and write Avro data that corresponds to a given format schema. The format schema can be defined either as a fully qualified class name of an Avro specific record or as an Avro schema string. If a class name is used, the class must be available in the classpath during runtime.

The Avro format can be used as follows:

.withFormat(
  new Avro()
    // required: define the schema either by using an Avro specific record class
    .recordClass(User.class)
    // or by using an Avro schema
    .avroSchema(
      "{" +
      "  \"type\": \"record\"," +
      "  \"name\": \"test\"," +
      "  \"fields\" : [" +
      "    {\"name\": \"a\", \"type\": \"long\"}," +
      "    {\"name\": \"b\", \"type\": \"string\"}" +
      "  ]" +
      "}"
    )
)

.with_format(
    Avro()
    # required: define the schema either by using an Avro specific record class
    .record_class("full.qualified.user.class.name")
    # or by using an Avro schema
    .avro_schema(
        "{"
        "  \"type\": \"record\","
        "  \"name\": \"test\","
        "  \"fields\" : ["
        "    {\"name\": \"a\", \"type\": \"long\"},"
        "    {\"name\": \"b\", \"type\": \"string\"}"
        "  ]"
        "}"
    )
)

format:
  type: avro
  # required: define the schema either by using an Avro specific record class
  record-class: "org.organization.types.User"
  # or by using an Avro schema
  avro-schema: >
    {
      "type": "record",
      "name": "test",
      "fields" : [
        {"name": "a", "type": "long"},
        {"name": "b", "type": "string"}
      ]
    }