> But then consider the same table. Except rows are typically updated once or > twice when they are new, and *then* go read only. And we also have a > process that at some point deletes *some* old rows (but not all - in fact, > only a small portion). > > In this case, the next INSERT once VACUUM has run is likely to stick a > "new" row somewhere very "far back" in the table, since there is now free > space there. This more or less completely ruins the BRIN index usability, > as the "old" blocks will now contain a single row from a "new" series.
Yeah. When we initially discussed BRIN, there was a mention of allowing a BRIN index to guide new tuple location -- something like auto-clustering, if you will. We haven't discussed the exact details but I think something along those lines is worth considering.
What I'm talking about is something that would be a lot simpler than auto-clustering. I'm not even talking about trying to detect if the row was about to go into the right place -- this might be expensive and certainly more complicated. I'm only talking about a simple case where we *never* put anything anywhere other than at the end of the table, period. That should make the check both cheap and simple.