I have added two tests that demonstrate the bug. The sync test passes and the async test fails.
add passing test for sync transforms of large files and failing test …
…for async transforms
Thanks, I will look at it as soon a possible, do u confirm the issue is with writting the header, not reading the columns?
Yes, the header gets written if transforms are synchronous - looks like some kind of race condition.
@wdavidw don't you maybe want to already merge the request? It doesn't change anything on the implementation - only demonstrates that there is a bug.