Sleepy0521 commented on PR #160:
URL:
https://github.com/apache/flink-connector-jdbc/pull/160#issuecomment-2785564098
> I am not sure this is a hotfix, please could you raise a Jira explaining
>
> * what the current issue with SQL Server is
> * why this is not being solved in the dialect. I do not think that
JdbcDynamicTablesource should have any reference to a specific dialect. Would
it be more appropriate to use the Select TOP for all dialect?
> * if the SQL Server issue was not causing a unit test failure - we need to
add a unit test in this area.
I applied for a Jira account but it hasn't been approved yet.
- The problem occurs when you use the SQL Server JDBC connector to query a
SQL Server table. If you don't add a LIMIT statement or any WHERE clause, the
Flink connector will query the entire table, which can impose IO pressure on
the SQL Server.
- For simple queries or tests where you only need to retrieve a few hundred
records, using the LIMIT statement would be more efficient. However, Flink
sqlserver connector does not support this feature. SqlServerDialect.java
```java
@Override
public String getLimitClause(long limit) {
throw new IllegalArgumentException("SqlServerDialect does not
support limit clause");
}
```
- why this is not being solved in the dialect. The JdbcDynamicTableSource
directly appends the LIMIT statement at the end of the query, even though SQL
Server clearly does not support this syntax. so, I added an if-else block in
JdbcDynamicTableSource
```java
if (limit >= 0) {
query = String.format("%s %s", query, dialect.getLimitClause(limit));
}
```
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
