Bernd Helmle wrote:
I've created a C-Function a while ago that extracts the TOAST size for a given relation. This gave me the opportunity to do a pg_relation_size(oid) + pg_relation_toast_size(oid) for a given table oid to calculate on disk data size required by a table. Maybe we should include such a function in core?
Writing such a thing is already on my to-do list; it's absolutely a missing piece of the puzzle here. If you've got such a patch, by all means submit that. I just ran into my first heavily TOASTy database recently and the way I'm computing sizes on the relations there is too complicated for my tastes, so it's completely unreasonable to expect regular users to do that.
To answer Rafael's concerns directly: you're right that this is confusing. pg_relation_size is always going to do what it does right now just because of how that fits into the design of the database. However, the documentation should be updated to warn against the issue with TOAST here. And it should be easier to get the total you're like to see here: main relation + toasted parts, since that's what most DBAs want in this area.
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