What does the buffered parameter do in Dapper dot net?

Question

Dapper dot net has a buffer parameter (a bool), but as far as I can tell the only thing it does is cast the result to a list before returning it.

A

Answer 1

In practice it is better to never use buffered: false.

I've found reading even many millions of rows that it is both faster and more memory efficient to use buffered results than unbuffered. Perhaps there is a cross over point if your tables have 500 columns and you're reading 10s of millions or 100s of millions of rows.

If your result sets are smaller than many billions of values it is not worth using buffered: false for any reason.

I was shocked during actual analysis that reading gigabytes of data from Sql Server was both faster (2-6x faster) and more memory efficient in standard buffered mode. The performance increase even accounts for the most minute operation possible, adding an object to a sparse array by index to an array that does not resize. Using a multi-gigabyte sparse array switching from unbuffered to buffered saw the 2x improvement in load time. Writing to a dictionary using buffered saw the 6x improvement in load time when inserting millions of records (dictionary used the table's int PK as key so as basic of a hashcode calculation as possible).

As with everything regarding performance you always must analyze. However I can tell you with a very high level of certainty always start with the default buffered behavior of Dapper.