DM MariaDB and FK compatibility clarification

dm/dm-compatibility-catalog.md

@@ -1,46 +1,56 @@
 ---
 title: Compatibility Catalog of TiDB Data Migration
-summary: This document describes the compatibility between DM of different versions and upstream/downstream databases.
+summary: This document describes the compatibility of TiDB Data Migration (DM) with upstream and downstream databases.
 ---
 
 # Compatibility Catalog of TiDB Data Migration
 
 DM supports migrating data from different sources to TiDB clusters. Based on the data source type, DM has four compatibility levels:
 
-- **Generally available (GA)**: The application scenario has been verified and passed the GA test.
-- **Experimental**: Although the application scenario has been verified, the test does not cover all scenarios or involves only a limited number of users. The application scenario might encounter problems occasionally.
-- **Not tested**: DM is expected to be always compatible with MySQL during iteration. However, due to resource constraints, not all MySQL forks are tested with DM. Therefore, the *not tested* source or target is technically compatible with DM, but is not fully tested, which means you need to verify its compatibility before you use.
-- **Incompatible**: DM is proved to be incompatible with the data source and the application is not recommended for use in production environments.
+- **Generally available (GA)**: The application scenario has been verified and passed GA testing.
+- **Experimental**: Common application scenarios have been verified, but coverage is limited or involves only a small number of users. Occasional issues are possible, so you need to verify compatibility in your specific scenario.
+- **Not tested**: DM aims to be compatible with the MySQL protocol and binlog. However, not all MySQL forks or versions are included in the DM test matrix. If a fork or version uses MySQL-compatible protocols and binlog formats, it is expected to work, but you must verify compatibility in your own environment before use.
+- **Incompatible**: DM has known blocking issues, so production use is not recommended.
 
 ## Data sources
 
-|Data source|Compatibility level|Remarks|
-|-|-|-|
-|MySQL ≤ 5.5|Not tested||
-|MySQL 5.6|GA||
-|MySQL 5.7|GA||
-|MySQL 8.0|GA|Does not support binlog transaction compression [Transaction_payload_event](https://dev.mysql.com/doc/refman/8.0/en/binary-log-transaction-compression.html)|
-|MariaDB < 10.1.2|Incompatible|Incompatible with binlog of the time type|
-|MariaDB 10.1.2 ~ 10.5.10|Experimental||
-|MariaDB > 10.5.10|Incompatible|Permission errors reported in the check procedure|
+| Data source | Compatibility level | Note |
+| - | - | - |
+| MySQL ≤ 5.5 | Not tested | |
+| MySQL 5.6 | GA | |
+| MySQL 5.7 | GA | |
+| MySQL 8.0 | GA | Does not support binlog transaction compression [Transaction_payload_event](https://dev.mysql.com/doc/refman/8.0/en/binary-log-transaction-compression.html). |
+| MariaDB < 10.1.2 | Incompatible | Incompatible with binlog of the time type. |
+| MariaDB 10.1.2 ~ 10.5.10 | Experimental | |
+| MariaDB > 10.5.10 | Not tested | Expected to work in most cases after bypassing the [precheck](/dm/dm-precheck.md). See [MariaDB notes](#mariadb-notes). |
+
+### Incompatibility with foreign key CASCADE operations
+
+- DM creates foreign key **constraints** on the target, but they are not enforced while applying transactions because DM sets the session variable [`foreign_key_checks=OFF`](/system-variables.md#foreign_key_checks).
+- DM does **not** support `ON DELETE CASCADE` or `ON UPDATE CASCADE` behavior by default, and enabling `foreign_key_checks` via a DM task session variable is not recommended. If your workload relies on cascades, **do not assume** that cascade effects will be replicated.
+
+### MariaDB notes
+
+- For MariaDB **10.5.11 and later**, the DM **precheck fails** due to privilege name changes (for example, `BINLOG MONITOR`, `REPLICATION SLAVE ADMIN`, `REPLICATION MASTER ADMIN`). The error appears as `[code=26005] fail to check synchronization configuration` in the replication privilege, dump privilege, and dump connection number checkers.
+- You can **bypass the precheck** by adding `ignore-checking-items: ["all"]` in the DM task. See [DM precheck](/dm/dm-precheck.md) for details.
 
 ## Target databases
 
 > **Warning:**
 >
-> DM v5.3.0 is not recommended. If you have enabled GTID replication but do not enable relay log in DM v5.3.0, data replication fails with low probability.
-
-|Target database|Compatibility level|DM version|
-|-|-|-|
-|TiDB 8.x|GA|≥ 5.3.1|
-|TiDB 7.x|GA|≥ 5.3.1|
-|TiDB 6.x|GA|≥ 5.3.1|
-|TiDB 5.4|GA|≥ 5.3.1|
-|TiDB 5.3|GA|≥ 5.3.1|
-|TiDB 5.2|GA|≥ 2.0.7, recommended: 5.4|
-|TiDB 5.1|GA|≥ 2.0.4, recommended: 5.4|
-|TiDB 5.0|GA|≥ 2.0.4, recommended: 5.4|
-|TiDB 4.x|GA|≥ 2.0.1, recommended: 2.0.7|
-|TiDB 3.x|GA|≥ 2.0.1, recommended: 2.0.7|
-|MySQL|Experimental||
-|MariaDB|Experimental||
+> DM v5.3.0 is not recommended. Enabling GTID replication without relay log in DM v5.3.0 might cause data replication to fail, although the probability is low.
+
+| Target database | Compatibility level | DM version |
+| - | - | - |
+| TiDB 8.x | GA | ≥ 5.3.1 |
+| TiDB 7.x | GA | ≥ 5.3.1 |
+| TiDB 6.x | GA | ≥ 5.3.1 |
+| TiDB 5.4 | GA | ≥ 5.3.1 |
+| TiDB 5.3 | GA | ≥ 5.3.1 |
+| TiDB 5.2 | GA | ≥ 2.0.7, recommended: 5.4 |
+| TiDB 5.1 | GA | ≥ 2.0.4, recommended: 5.4 |
+| TiDB 5.0 | GA | ≥ 2.0.4, recommended: 5.4 |
+| TiDB 4.x | GA | ≥ 2.0.1, recommended: 2.0.7 |
+| TiDB 3.x | GA | ≥ 2.0.1, recommended: 2.0.7 |
+| MySQL | Experimental | |
+| MariaDB | Experimental | |