| From: | Andrei Lepikhov <lepihov(at)gmail(dot)com> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Problems with estimating OR conditions, IS NULL on LEFT JOINs |
| Date: | 2025-04-17 12:47:39 |
| Message-ID: | c15ffae1-0786-4aff-8e93-00675d6d3dc5@gmail.com |
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| Lists: | pgsql-hackers |
On 6/24/23 13:23, Tomas Vondra wrote:
> I really hope what I just wrote makes at least a little bit of sense.
Here is a continuation of your work:
1. non-matched estimation sophisticated to provide meaningful numbers.
2. unmatched_frac is stored in sjinfo that let us to summarise these
generated nulls along the tree of outer joins.
3. unmatched_frac is used not only for nulltest estimation but also for
correction of stanullfrac and stadistinct values (improves GROUP-BY).
4. EXPLAIN prints number of estimated and actually generated NULLs in
outer-join nodes.
This patch no less ugly than your, may be even more. Tambien, not sure
it became more meaningful. But it helps being applied to some reported
cases I have ;).
--
regards, Andrei Lepikhov
| Attachment | Content-Type | Size |
|---|---|---|
| 0001-Consider-number-of-nulls-generated-by-inner-side-of-.patch | text/x-patch | 32.3 KB |
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