代码逻辑性错误，位于:plugin-rdbms-util/src/main/java/com/alibaba/datax/plugin/rdbms/writer/util/WriterUtil.java

https://github.com/alibaba/DataX/blob/master/plugin-rdbms-util/src/main/java/com/alibaba/datax/plugin/rdbms/writer/util/WriterUtil.java
122行 if (forceUseUpdate ||
((dataBaseType == DataBaseType.MySql || dataBaseType == DataBaseType.Tddl) && writeMode.trim().toLowerCase().startsWith("update"))
) {
逻辑反了吧，这里应该执行replace而不是insert

Open plugin-rdbms-util/src/main/java/com/alibaba/datax/plugin/rdbms/writer/util/WriterUtil.java and inspect line 122 with the surrounding write-mode logic. Check the forceUseUpdate and MySql/Tddl conditions to confirm whether they select replace rather than insert. Done means the condition matches the intended write behavior without changing unrelated database modes.

Written by the indexing model from the issue text.