DM task pause with Specified key was too long

[Christophe-4567]

What did you do?

followed the documentation: https://docs.pingcap.com/tidb/stable/migrate-large-mysql-to-tidb
everything went fine until the DM part.
v540_1.zip

What did you expect to see?

the task running and keeping the tidb cluster sync with the maria db

What did you see instead?

query-status return: "RawCause": "[ddl:1071]Specified key was too long; max key length is 3072 bytes"

Versions of the cluster

DM version (run dmctl -V or dm-worker -V or dm-master -V):

dm-master -V: Release Version: v5.4.0
dm-worker -V: Release Version: v5.4.0
dmctl : v5.4.0

Upstream MySQL/MariaDB server version:

10.4.18-MariaDB

Downstream TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

5.4.0

How did you deploy DM: tiup or manually?

TiUP

Other interesting information (system version, hardware config, etc):

- set max-index-lengh to 12288 
- Try to use DM 5.3.1 (as Daniël on asktug on slack did ask)

current status of DM cluster (execute query-status <task-name> in dmctl)

Starting component `dmctl`: /root/.tiup/components/dmctl/v5.3.1/dmctl/dmctl /root/.tiup/components/dmctl/v5.3.1/dmctl/dmctl --master-addr xxx:8261 query-status task-xxx
{
    "result": true,
    "msg": "",
    "sources": [
        {
            "result": true,
            "msg": "",
            "sourceStatus": {
                "source": "mysql-dc3-master",
                "worker": "dm-xxx-8262",
                "result": null,
                "relayStatus": null
            },
            "subTaskStatus": [
                {
                    "name": "task-xxx",
                    "stage": "Paused",
                    "unit": "Sync",
                    "result": {
                        "isCanceled": false,
                        "errors": [
                            {
                                "ErrCode": 44003,
                                "ErrClass": "schema-tracker",
                                "ErrScope": "downstream",
                                "ErrLevel": "high",
                                "Message": "startLocation: [position: (, 0), gtid-set: ], endLocation: [position: (mariadb-bin.048312, 96376516), gtid-set: 0-1856393171-6399440815]: failed to create table for `ringover`.`cdn_storage` in schema tracker",
                                "RawCause": "[ddl:1071]Specified key was too long; max key length is 3072 bytes",
                                "Workaround": ""
                            }
                        ],
                        "detail": null
                    },
                    "unresolvedDDLLockID": "",
                    "sync": {
                        "totalEvents": "52",
                        "totalTps": "0",
                        "recentTps": "0",
                        "masterBinlog": "(mariadb-bin.048944, 34179712)",
                        "masterBinlogGtid": "0-1856393171-6452464976",
                        "syncerBinlog": "(mariadb-bin.048312, 96375851)",
                        "syncerBinlogGtid": "0-1856393171-6399440815",
                        "blockingDDLs": [
                        ],
                        "unresolvedGroups": [
                        ],
                        "synced": false,
                        "binlogType": "remote",
                        "secondsBehindMaster": "0"
                    }
                }
            ]
        }
    ]
}

[lance6716]

I think we should let DM's schema tracker (embedded TiDB) always uses the configuration with max compatibility. Will check it later.