ClassifyEvent() does not recognize DROP FOREIGN KEY causing CheckpointTS stuck

What did you do?

1. Start a cluster

   tiup playground-ng v8.5.8 --db 1 --kv 1 --pd 1 --tiflash 0 --ticdc 1 --ticdc.config ./ticdc-newarch.toml
   

2. Prepare changefeed config, containing at least one arbitrary event filter

   [filter]
   [[filter.event-filters]]
   matcher = ['*.*']
   ignore-event = ['delete']
   

3. Create a changefeed

   tiup cdc:v8.5.8 cli changefeed create -c test-8732 --sink-uri 'blackhole://' --config ./config-8732.toml
   

4. Create a table with foreign key

   use test;
   -- set global tidb_enable_dist_task = 0;
   -- set global tidb_ddl_enable_fast_reorg = 0;
   create table b (id bigint primary key);
   create table a (id bigint primary key, b bigint, foreign key fk_1 (b) references b (id));
   

5. Drop the foreign key

   alter table a drop foreign key fk_1;
   

What did you expect to see?

No response

What did you see instead?

• CheckpointTS is now stuck.
• CDC log keeps showing errors logs like this every second:

[ERROR] [event_broker.go:726] ["scan events failed"] [changefeedID=default/test-8732] [dispatcherID=62170044884923103651170238435157499028] [tableID=134] [dataRange="{\"ClusterID\":0,\"Span\":{\"TableID\":134,\"StartKey\":\"dIAAAAAAAAD/hl9yAAAAAAD6\",\"EndKey\":\"dIAAAAAAAAD/hl9zAAAAAAD6\"},\"CommitTsStart\":469142236153511947,\"CommitTsEnd\":469142250899111940,\"LastScannedTxnStartTs\":0}"] [receivedResolvedTs=469142251162304517] [sentResolvedTs=469142236153511947] [error="event type drop foreign key not valid"] 

Restarting changefeed cannot fix the lag.

Versions of the cluster

v8.5.8

Reproduce the issue with the provided TiUP, changefeed, table-creation, and DROP FOREIGN KEY commands, then inspect ClassifyEvent() and the CDC error showing "event type drop foreign key not valid." No source file or test is named in the report. Done means DROP FOREIGN KEY is recognized and the changefeed's CheckpointTS no longer remains stuck.