ADF throws error: Unexpected error encountered filling record reader buffer ClassCastException

This post has been republished via RSS; it originally appeared at: New blog articles in Microsoft Tech Community.

Today we want to write about a very interesting case that our team  Prathibha Vemulapalli, Charl Roux, and I worked this very week.


A parquet file was created with more than 100 columns to be imported on the AzureDW using Azure Data Factory. The file had diverse datatypes. So, before I go more deeply on the error and the troubleshooting process. Let me share step by step of the environment. 


Put in a simple way. This environment has a parquet file as source, SQL DW as destination running on ADF.

As figure 1,2 and 3 shows:



 Figure 1: Define Blob Storage







Figure 2: Define Parquet file 




Figure 3: Define Source file


The destination is SQL DW as figure 4 shows:



Figure 4: Define data destination


Once the table was defined on the SQLDW connector. A pipeline must be created with the source (parquet), Sink (SQLDW) as figure 5 shows:



Figure 5: pipeline


Publish all changes, rename the pipeline to a suitable name.


More details here about data factory you can find here:


Our environment is ready to debug. Once I run the pipeline ( debug option) it will hit the condition I mentioned before:




Figure 6: ADF Cast error



The table was defined with data types like Int, DateTime, nVarchar , Float, and Real. More than 100 rows and the error was::

“Error happened when loading data into SQL Data Warehouse.,Source=Microsoft.DataTransfer.ClientLibrary,''Type=System.Data.SqlClient.SqlException,Message=HdfsBridge::recordReaderFillBuffer - Unexpected error encountered filling record reader buffer: ClassCastException: class java.lang.Integer cannot be cast to class (java.lang.Integer is in module java.base of loader 'bootstrap'; is in unnamed module of loader 'app'),Source=.Net SqlClient Data Provider,SqlErrorNumber=106000,Class=16,ErrorCode=-2146232060,State=1,Errors=[{Class=16,Number=106000,State=1,Message=HdfsBridge::recordReaderFillBuffer - Unexpected error encountered filling record reader buffer"


Discussing in your team this error was spotted:  ClassCastException: class java.lang.Integer cannot be cast to class

But which one from the 100 columns?


Once your main table accepts null values you can test by excluding the columns from a certain datatype. For example, try to exclude all the int columns from your transformation see if it works and so on so forth until you find the on to blame, as figure 7 shows:





Figure 7: Delete column to be imported


Note in ADF, once you click on the transformation you can check the schema and also preview the source data. If you changed a datatype you can clear to refresh and import the schema again as figure8  shows:




Figure 8: ADF Metadata


In our case, the suitable solution found by the customer was recreated the parquet file using INT96 instead of INT32 which raised the error mentioned on date columns.


Once you spot this error, you will need to review the data types on the table and work on it.


That was great CSS teamwork


Liliam C Leme

REMEMBER: these articles are REPUBLISHED. Your best bet to get a reply is to follow the link at the top of the post to the ORIGINAL post! BUT you're more than welcome to start discussions here:

This site uses Akismet to reduce spam. Learn how your comment data is processed.