Seth Hollyman created ARROW-13191:
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             Summary: [Go] Support external schema in ipc readers
                 Key: ARROW-13191
                 URL: https://issues.apache.org/jira/browse/ARROW-13191
             Project: Apache Arrow
          Issue Type: Improvement
          Components: Go
            Reporter: Seth Hollyman


(Apologies if I'm imprecise here, I'm still coming up to speed on the arrow 
details.)

 

The IPC message format describes how data and metadata messages are 
encapsulated, but it is not a requirement that each message must include the 
schema.

 

In Go, github.com/apache/arrow/go/arrow/ipc contains NewReader() for setting up 
reading of IPC messages, and accepts the option WithSchema to pass the schema 
into said reader.  However, the implementation merely uses that information to 
compare that the schema it reads from the IPC stream matches the passed in 
reader.  This request is to allow WithSchema to behave as expected, and use the 
option-provided Schema for performing reads.

 

The one gotcha here appears to be the dictionary type map, which is currently 
retained independently of the schema but is part of the internal readSchema() 
setup. Completeness may warrant another option for communicating those 
externally as well?  Or perhaps option-passed Schema should be documented to 
not support dictionary types?



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