On Mon, 2025-01-27 at 10:13 +0100, Benoit Lobréau wrote: > On 1/25/25 7:07 PM, Laurenz Albe wrote: > > Looks good to me. I have one question left: the explanation for the > > performance > > penalty of a high leaf fragmentation sounds like it would only be relevant > > for > > disks where sequential reads are faster. If that is correct, perhaps it > > would be > > worth mentioning. > > Frederic noticed a performance hit even for on his laptop with a SSD. > > On Fri, 2025-01-24 at 15:41 +0100, Frédéric Yhuel wrote: > > I've noticed that maximum leaf_fragmentation can have a huge impact on > > a range index-only scan, when reading all blocs from disks, even on my > > laptop machine with SSD, but I don't know if this is the right place > > to document this? > > He reported to our team, that he did a test with two indexes on the same > data. They had the same density but one had no fragmentation while the > other had 100%. He got an execution time of ~90ms (0 frag) vs ~340ms > 100% frag). > > I get similar result with my laptor (except my disk is significantly > worse: ~152ms vs ~833ms).
Thanks for checking. I'll set the patch "ready for committer". I personally would still like to know how fragmentation slows down performance. Yours, Laurenz Albe
