jgehrcke commented on issue #14968:
URL: https://github.com/apache/arrow/issues/14968#issuecomment-1355168902

   Understood the problem :).
   
   Manual bisection has shown that this line is where things crash:
   
   
https://github.com/apache/arrow/blob/41b57d683ea73329af083540e6f67007bdd1d0c4/python/pyarrow/_dataset.pyx#L778
   
   `sp.get()` above returns whatever `self.format.DefaultWriteOptions()` 
[here](https://github.com/apache/arrow/blob/41b57d683ea73329af083540e6f67007bdd1d0c4/python/pyarrow/_dataset.pyx#L890)
 returns.
   
   And in case of the ORC file format that's 
   
   ```cpp 
   std::shared_ptr<FileWriteOptions> OrcFileFormat::DefaultWriteOptions() {
     // TODO (https://issues.apache.org/jira/browse/ARROW-13796)
     return nullptr;
   }
   ```
   
   as defined in 
[cpp/src/arrow/dataset/file_orc.cc](https://github.com/apache/arrow/blob/41b57d683ea73329af083540e6f67007bdd1d0c4/cpp/src/arrow/dataset/file_orc.cc#L221).
   
   Trying to invoke `type_name()` of `nullptr` explains the segfault.
   
   Quote from JIRA ticket:
   
   > https://github.com/apache/arrow/pull/10991 added basic support for ORC 
file format in the Datasets API, but didn't yet add support to write datasets 
to the ORC format.
   
   https://arrow.apache.org/docs/python/dataset.html#dataset currently says:
   
   > Currently, only Parquet, ORC, Feather / Arrow IPC, and CSV files are 
supported. 
   
   That kind of suggests that ORC support is complete.
   
   However, the [`write_dataset()` 
docs](https://arrow.apache.org/docs/python/generated/pyarrow.dataset.write_dataset.html#pyarrow.dataset.write_dataset)
 are explicit in the sense that ORC is _not_ documented as being supported:
   
   >  Currently supported: “parquet”, “ipc”/”arrow”/”feather”, and “csv”.
   
   
   
   
   
   
   
   


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