What is the best way to convert a very large parquet table to delta ? possibly without downtime!

[User16783853501]

What is the best way to convert a very large parquet table to delta ? possibly without downtime! 

[sajith_appukutt]

You could run in-place convert with

CONVERT TO DELTA parquet.`/data-pipeline/`
CREATE TABLE events USING DELTA LOCATION '/data-pipeline/'

This command lists all objects in the path, infers the data schema by reading the footers of all parquet files and creates the necessary metadata / statistics. This would be the least disruptive approach as you are not copying data over.

If you have multiple external tables share the same underlying parquet directory, you'd need to run convert for all of them

[brickster_2018]

I vouch for Sajith's answer. The main advantage with "CONVERT TO DELTA" is that operations are metadata centric which means we are not reading the full data for the conversion. For any other file format conversion, it's necessary to read the data completely and write it to the target format.