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kurnoolsaketh merged 3 commits into from
May 6, 2026
Merged

Add Avro -> Kafka Connect type mapping and unsupported avro schemas #6081

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add avro -> KC type mapping and unsupported avro schemas
kurnoolsaketh Apr 18, 2026
5788562
change unsupported data types to "unsupported schemas"
kurnoolsaketh Apr 24, 2026
f7c786a
sergey review comments
kurnoolsaketh May 5, 2026
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110 changes: 89 additions & 21 deletions docs/integrations/data-ingestion/kafka/kafka-clickhouse-connect-sink.md
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Expand Up @@ -138,27 +138,27 @@ Sink, use [Kafka Connect Transformations](https://docs.confluent.io/platform/cur

**With a schema declared:**

| Kafka Connect Type | ClickHouse Type | Supported | Primitive |
| --------------------------------------- |-----------------------| --------- | --------- |
| STRING | String | ✅ | Yes |
| STRING | JSON. See below (1) | ✅ | Yes |
| INT8 | Int8 | ✅ | Yes |
| INT16 | Int16 | ✅ | Yes |
| INT32 | Int32 | ✅ | Yes |
| INT64 | Int64 | ✅ | Yes |
| FLOAT32 | Float32 | ✅ | Yes |
| FLOAT64 | Float64 | ✅ | Yes |
| BOOLEAN | Boolean | ✅ | Yes |
| ARRAY | Array(T) | ✅ | No |
| MAP | Map(Primitive, T) | ✅ | No |
| STRUCT | Variant(T1, T2, ...) | ✅ | No |
| STRUCT | Tuple(a T1, b T2, ...) | ✅ | No |
| STRUCT | Nested(a T1, b T2, ...) | ✅ | No |
| STRUCT | JSON. See below (1), (2) | ✅ | No |
| BYTES | String | ✅ | No |
| org.apache.kafka.connect.data.Time | Int64 / DateTime64 | ✅ | No |
| org.apache.kafka.connect.data.Timestamp | Int32 / Date32 | ✅ | No |
| org.apache.kafka.connect.data.Decimal | Decimal | ✅ | No |
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@kurnoolsaketh kurnoolsaketh Apr 18, 2026

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fixed table formatting, no content changes

| Kafka Connect Type | ClickHouse Type | Supported | Primitive |
|-----------------------------------------|--------------------------|-----------|-----------|
| STRING | String | ✅ | Yes |
| STRING | JSON. See below (1) | ✅ | Yes |
| INT8 | Int8 | ✅ | Yes |
| INT16 | Int16 | ✅ | Yes |
| INT32 | Int32 | ✅ | Yes |
| INT64 | Int64 | ✅ | Yes |
| FLOAT32 | Float32 | ✅ | Yes |
| FLOAT64 | Float64 | ✅ | Yes |
| BOOLEAN | Boolean | ✅ | Yes |
| ARRAY | Array(T) | ✅ | No |
| MAP | Map(Primitive, T) | ✅ | No |
| STRUCT | Variant(T1, T2, ...) | ✅ | No |
| STRUCT | Tuple(a T1, b T2, ...) | ✅ | No |
| STRUCT | Nested(a T1, b T2, ...) | ✅ | No |
| STRUCT | JSON. See below (1), (2) | ✅ | No |
| BYTES | String | ✅ | No |
| org.apache.kafka.connect.data.Time | Int64 / DateTime64 | ✅ | No |
| org.apache.kafka.connect.data.Timestamp | Int32 / Date32 | ✅ | No |
| org.apache.kafka.connect.data.Decimal | Decimal | ✅ | No |

- (1) - JSON is supported only when ClickHouse settings has `input_format_binary_read_json_as_string=1`. This works only for RowBinary format family and the setting affects all columns in the insert request so they all should be a string. Connector will convert STRUCT to a JSON string in this case.

Expand Down Expand Up @@ -249,6 +249,74 @@ The connector can consume data from multiple topics
}
```

###### Avro type mapping {#avro-type-mapping}
The type mapping below is defined by `io.confluent.connect.avro.AvroConverter`, the official Avro serializer/deserializer implementation in Kafka Connect. See the Kafka Connect [docs](https://docs.confluent.io/platform/current/connect/userguide.html#avro) for advanced information on conversion logic.

✅: Supported
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@chernser chernser May 5, 2026

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similar as for protobuf docs

  • mention what converter should be used
  • additional documentation links
  • structure type mapping -> avro/proto mapping


❌: Not supported

️⚠️: Partially supported

| Avro Type | Kafka Connect Type | Supported | Notes |
|-----------|--------------------|-----------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| null | _N/A_ | ❌ | Not supported as a standalone type, but can be used in unions |
| boolean | BOOLEAN | ✅ | |
| int | INT8/INT16/INT32 | ✅ | Defaults to INT32. Resolves to INT8 if the schema has property `connect.type=int8` (analagously for INT16 if `connect.type=int16`) |
| long | INT64 | ✅ | |
| float | FLOAT32 | ✅ | |
| double | FLOAT64 | ✅ | |
| bytes | BYTES | ✅ | |
| string | STRING | ✅ | |
| record | STRUCT | ✅ | |
| enum | STRING | ✅ | |
| array | ARRAY/MAP | ✅ | Defaults to ARRAY. Resolves to MAP if the field was originally constructed via `AvroData.fromConnectSchema` ([source](https://github.com/confluentinc/schema-registry/blob/174907bfc0d9424e8d02e788f450f4afcdda1750/avro-data/src/main/java/io/confluent/connect/avro/AvroData.java#L943)) |
| map | MAP | ✅ | |
| union | STRUCT/`<T>` | ⚠️ | Defaults to STRUCT. Resolves to the singleton type `T` in the union definition if `flatten.singleton.unions=true` (see [docs](https://docs.confluent.io/cloud/current/connectors/reference/connector-configuration.html#value-converter-flatten-singleton-unions)) |
| fixed | BYTES | ⚠️ | Fixed `decimal` logical type is not supported (see below) |

Refer to [Supported data types](#supported-data-types) for the mapping between Kafka Connect types and ClickHouse types.

###### Unsupported Avro schemas {#unsupported-avro-schemas}

The following Avro schemas are unsupported by the connector:
- fixed `decimal` logical type
```json
{"name": "decimal_18_4", "type": "fixed", "size": 8, "logicalType": "decimal", "precision": 18, "scale": 4}
```
- nullable unions
```json
{"name": "mixed_union", "type": ["null", "string", "int"], "default": null}
```
- record unions
```json
{
"name": "record_union",
"type": [
{
"type": "record",
"name": "TypeA",
"fields": [
{
"name": "label",
"type": "string"
}
]
},
{
"type": "record",
"name": "TypeB",
"fields": [
{
"name": "count",
"type": "int"
}
]
}
]
}
```

##### Protobuf schema support {#protobuf-schema-support}

```json
Expand Down
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