On Sat, Aug 28, 2021 at 6:53 AM Tomas Vondra <tomas.von...@enterprisedb.com> wrote:
> Hi, > > The attached patch series is modified to improve estimates for these > special clauses (Var op Var with the same var on both sides) without > extended statistics. This is done in 0001, and it seems fairly simple > and cheap. > > The 0002 part is still the same patch as on 2021/07/20. Part 0003 fixes > handling of those clauses so that we don't treat them as simple, but it > does that by tweaking statext_is_compatible_clause(), as suggested by > Dean. It does work, although it's a bit more invasive than simply > checking the shape of clause in statext_mcv_clauselist_selectivity. > > I do have results for the randomly generated queries, and this does > improve the situation a lot - pretty much all the queries with (a=a) or > (a<a) clauses had terrible estimates, and this fixes that. > > That being said, I'm still not sure if this is an issue in real-world > applications, or whether we're solving something because of synthetic > queries generated by the randomized generator. But the checks seem > fairly cheap, so maybe it doesn't matter too much. > > > regards > > -- > Tomas Vondra > EnterpriseDB: http://www.enterprisedb.com > The Enterprise PostgreSQL Company > Hi, For 0001-Improve-estimates-for-Var-op-Var-with-the-s-20210828.patch : + * form (variable op variable) with the save variable on both sides. typo: save -> same Cheers
