On Thu, 14 Mar 2019 at 21:12, Edmund Horner <ejr...@gmail.com> wrote:
> I'm not sure how an unreasonable underestimation would occur here. If > you have a table bloated to say 10x its minimal size, the estimator > still assumes an even distribution of tuples (I don't think we can do > much better than that). So the selectivity of "ctid >= <last ctid > that would exist without bloat>" is still going to be 0.9. Okay, think you're right there. I guess the only risk there is just varying tuple density per page, and that seems no greater risk than we have with the existing stats. Just looking again, I think the block of code starting: + if (density > 0.0) needs a comment to mention what it's doing. Perhaps: + /* + * Using the average tuples per page, calculate how far into + * the page the itemptr is likely to be and adjust block + * accordingly. + */ + if (density > 0.0) Or some better choice of words. With that done, I think 0001 is good to go. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
