topic Re: Disk cache for csv file in Databricks in Data Engineering

Disk cache for csv file in Databricks

NhanNguyen — Thu, 23 May 2024 06:57:41 GMT

Dear team,

I'm investigate to improve performance when reading large csv file as input and find this https://learn.microsoft.com/en-us/azure/databricks/optimizations/disk-cache.

I just wonder Do disk-cache also apply for csv file?

Thanks!

Re: Disk cache for csv file in Databricks

-werners- — Thu, 23 May 2024 09:30:30 GMT

The answer is "yes but".
If you read a csv into a dataframe, and apply a cache action, no matter what file format, it will be cached (if spark can read it of course).
That being said: spark applies lazy evaluation. So this means the csv is only actually read when an action is executed (like write, count, ...). Before that Spark will only generate a query plan.
So to speed up your code, it is important to find out what the best location is to apply the cache. Because caching is an expensive operation (it actually writes the data to disk) and it will only come in handy if the cached dataframe is used more than once afterwards.
Not sure if that makes sense?

Re: Disk cache for csv file in Databricks

-werners- — Thu, 23 May 2024 09:33:49 GMT

To add on that: Disk cache (formerly detla cache/dbio cache) automates some things, but the principle remains:
you will only gain if the cached df is used multiple times.

Re: Disk cache for csv file in Databricks

NhanNguyen — Thu, 23 May 2024 16:00:53 GMT

Thanks @-werners-,

That's right, I tried and get some significantly performance.