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https://issues.apache.org/jira/browse/FLINK-16048?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17159773#comment-17159773
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Dawid Wysakowicz commented on FLINK-16048:
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[~ykt836] IMO, we need both. The *schema-string* is the schema that the program
expects. I think of it as the schema of the Table that was frozen at compile
time. It is either the schema of the {{SpecificRecord}} we work with
(irrelevant from the point of view of RowData) or the latest schema retrieved
from the schema-registry when compiling the query. It is needed to e.g. provide
a default value for a field that was introduced in a later version of schema.
Imagine a case:
Schema 1: has fields "field1", "field2"
Schema 2: added "field3" with default value "ABC" <- we executed a query at
this point in time and we use the "field3"
If we do not pass the schema 2 as the "schema-string", then when we encounter a
record written with Schema 1, we don't know how to provide the "field3" and our
query fails.
> Support read/write confluent schema registry avro data from Kafka
> ------------------------------------------------------------------
>
> Key: FLINK-16048
> URL: https://issues.apache.org/jira/browse/FLINK-16048
> Project: Flink
> Issue Type: Improvement
> Components: Formats (JSON, Avro, Parquet, ORC, SequenceFile), Table
> SQL / Ecosystem
> Affects Versions: 1.11.0
> Reporter: Leonard Xu
> Assignee: Danny Chen
> Priority: Major
> Labels: pull-request-available, usability
> Fix For: 1.12.0
>
>
> *The background*
> I found SQL Kafka connector can not consume avro data that was serialized by
> `KafkaAvroSerializer` and only can consume Row data with avro schema because
> we use `AvroRowDeserializationSchema/AvroRowSerializationSchema` to se/de
> data in `AvroRowFormatFactory`.
> I think we should support this because `KafkaAvroSerializer` is very common
> in Kafka.
> and someone met same question in stackoverflow[1].
> [[1]https://stackoverflow.com/questions/56452571/caused-by-org-apache-avro-avroruntimeexception-malformed-data-length-is-negat/56478259|https://stackoverflow.com/questions/56452571/caused-by-org-apache-avro-avroruntimeexception-malformed-data-length-is-negat/56478259]
> *The format details*
> _The factory identifier (or format id)_
> There are 2 candidates now ~
> - {{avro-sr}}: the pattern borrowed from KSQL {{JSON_SR}} format [1]
> - {{avro-confluent}}: the pattern borrowed from Clickhouse {{AvroConfluent}}
> [2]
> Personally i would prefer {{avro-sr}} because it is more concise and the
> confluent is a company name which i think is not that suitable for a format
> name.
> _The format attributes_
> || Options || required || Remark ||
> | schema-string | true | avro schema string used for (de)serialization |
> | schema-registry.url | true | URL to connect to schema registry service |
> | schema-registry.subject | false | Subject name to write to the Schema
> Registry service, required for sink |
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