FAQs¶

Q: What are the differences between enabling and disabling the cross-source analysis function when starting a data federation channel?¶

A: Enabling the cross-source analysis function requires more resource request than disabling the function. Cross-source analysis supports accessing data from multiple data sources by unified SQL statements. Using a channel with cross-source analysis disabled, you can query data from a single data source only (currently supporting MySQL and Hive data sources with the corresponding querying syntax). Besides querying data, you can also download data from Hive data sources with the Federation Download feature.

Q: When configuring JDBC connection in Tableau to access data in Hive through a read channel with cross-source analysis disabled, there is no response, or an error will be reported. How to solve this issue?¶

A: Currently, Data Federation does not support JDBC connection in Tableau to access data in Hive through a read channel with cross-source analysis disabled

Q: Why does a timeout error occur when accessing Hive data source through a read channel with cross-source analysis disabled by JDBC?¶

A: If aggregation or sorting statements like group by, count, and order by are used for data query, the mapreduce jobs will be started in Hive, which leads to minute-level running and response time. It is recommended to access data in Hive through a read channel with cross-source analysis enabled or use the Federation Download feature.

Q: When does an error occur when using query statements as follows?¶

SELECT * FROM mysql.test.data LEFT JOIN hive.db.device ON mysql.test.data.dev_id=hive.db.device.dev_id WHERE hive.db.device.dev_id IS NOT NULL
hive

A: Name like hive.db.device.dev_id is too long. It is recommended to use an alias. The query statement can be changed to:

SELECT * FROM mysql.test.data m LEFT JOIN hive.db.device h ON m.dev_id=h.dev_id WHERE h.dev_id IS NOT NULL

Q: The read channel is started successfully, but a message “Schema does not exit” is reported when querying data. Why?¶

A: This error might be caused by network connection or component dependency issues. The data source is not added correctly. Try restarting the channel.

Q: When dragging data in Tableau or IDE, an error about invalid SQL is reported. Why?¶

A: Data Federation cannot fit Tableau or IDE fully because it has special requirements on data source, database, and table names. It is recommended to use custom SQL statements or enter SQL in the IDE Console to query data.