Re: FDW handling count(*) through AnalyzeForeignTable or other constant time push-down

Hey all,

 

I’m building a FDW around a column-store backend (similar to CStore but for genomic data!).

 

I have tables in the billions of rows, and have a common query pattern of asking for the table size (i.e. SELECT COUNT(*) FROM big_fdw_table; ).

 

This is a read-optimized system in which I know in constant time the exact dimensions of the table.

 

Is there any way to convince Postgres FDW to leverage the analyze row counts or even the “double* totalRowCount” returned from the AcquireSampleRows callback from my AnalyzeForeignTable function so that it does not do a full-table scan for a COUNT(*) etc?

 

My current fallback is to export a specialized function that returns the table row count for a given FDW table, but that then leaks into the user-application driving these queries.