Thank you very much for your feedback on this.
The tmp space free is 300GB and the DB is 3 GB. We did find that we needed more space in our innodb buffer pool and log file size, but even after that it still fails.
We did add an explicit setting for the tmp dir.
The companion plugin / index has been installed and worked fine. Can you send me the SQL it is running and I can run it inside tables plus?
Thank you,
Dave