Changefeed in Avro format does not include mvcc_timestamp when option is specified

[jonstjohn]

Describe the problem

When a changefeed is created using WITH mvcc_timestamp and Avro format, the mvcc_timestamp never gets emitted in the message. Using WITH updated works for emitting the updated timestamp, but mvcc_timestamp is required to accurately include the timestamp during an initial scan.

To Reproduce

Setup a confluent schema registry.

Run cockroach demo.

Run the following sinkless changefeed:

CREATE CHANGEFEED FOR TABLE movr.users 
WITH 
        updated ,
        full_table_name
        , mvcc_timestamp    
        , format = avro
        , envelope = wrapped
        , confluent_schema_registry = 'http://127.0.0.1:8081/'       
        , schema_change_events = column_changes
        , schema_change_policy = nobackfill
        , kafka_sink_config='{"RequiredAcks": "ALL", "Compression": "GZIP"}'   
        , initial_scan = 'no'
        ;

Insert a row into the movr.users table. Notice that the changefeed message does not have the mvcc_timestamp field.

Expected behavior
The mvcc_timestamp field is included, similar to how it is included when using json format.

Environment:

• CockroachDB version 23.2.2
• Server OS: Linux
• Client app: cockroach sql

Additional context
The only other option is to use the updated field, which does not accurately reflect the mvcc_timestamp during initial scan or backfill.

Jira issue: CRDB-38190

Epic CRDB-41784

[keljopap]

Just noting we are seeing this with the experimental change feed on Cockroach v23.1.17 as well.

[blathers-crl]

cc @cockroachdb/cdc

[blathers-crl]

Based on the specified backports for linked PR #129840, I applied the following new label(s) to this issue: branch-release-24.1.8-rc. Please adjust the labels as needed to match the branches actually affected by this issue, including adding any known older branches.

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