Aborted quiet backend connection during long Export

[philrz]

This issue was originally reported by a community user in a public Slack thread. In their own words:

For the past few Zui releases, I have not been able to export to CSV (currently using v0.30.1-135). Having the same issue with exporting to ZNG. It keeps throwing "Error Exporting" after several seconds.

After some debug, they provided the following DevTools screenshot during the failure:

Now having an idea of the root cause, here's own own repro of the problem on Windows 10 using Zui Insiders 0.30.1-136. To prep, I loaded the Zed sample data a couple dozen times to the same pool, then executed the query count() by ts | sort ts | sort count | sort ts | sort count while also asking the app for an Export of the same query response in CSV. What's key about this query is that the aggregation and sorts cause the backend to chew for a long time before returning any data, which keeps the connection quiet and hence vulnerable to timeout. A simple export of a full data set that constantly streams data does not seem to trigger the issue.

Repro.mp4

[philrz]

Verified in Zui Insiders 0.30.1-137.

As shown in the attached video, the Export now completes successfully after several minutes with no abort.

Verify.mp4

#2614 has also been opened to track future enhancements here such as adding a "Cancel" option during Export.

Thanks @jameskerr!