What are best possible options for rollback if something broke up after the upgrade. I have tried the taking a backup from 6.7 and tried restoring them in 5.8 cluster which did not work as expected.
Please let me know if there is any safer options to rollback or take any precautions in case of issues after upgrading to 6.7.
You can’t restore a backup of a newer version onto an older version, and downgrading MemSQL is not possible without creating a new cluster and reloading the data into it. Your options include:
Take a backup of MemSQL prior to upgrading (this is always recommended anyway). You can restore this backup later if necessary, to restore the pre-upgrade state.
You can export the data from MemSQL into CSV files or any similar format, and import them back into MemSQL. This works across versions, including new to old. You can use any tool for exporting/importing data in logical (not physical) format from MySQL - a simple example is mysqldump, and there are many others. Or you can always do it manually with SELECT INTO OUTFILE / LOAD DATA.