How To Calculate Table Size Minus Deleted Rows

I'm in the need of a way to determine the disk size of a table that
excludes dead tuples. Here is my situation. Our company would like to
provide a "rolling storage" solution on a per schema basis. So
basically we set a "quota" of the amount of disk space that a schema can
occupy. Every night a cron job is run that calculates the overage of
each schema's quota and deletes as many rows as necessary from each
table to bring the schema back within quota limits.

I was trying to use pg_total_relation_size to calculate the amount of
space consumed by each table, but I quickly learned that even after
deleting/vacuuming, the reported size of the table does not drop. I
assume this is due to the nature of how a lazy vacuum works. Is there a
way to get the size of the table that excludes the freed (but not
released) space from a delete/vacuum run?

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Brian Helm
Security Confidence Corporation
Brian(dot)Helm(at)SecurityConfidence(dot)com
513.388-4500/866.732.2661 Ext 106
www.SecurityConfidence.com