| From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
|---|---|
| To: | Tender Wang <tndrwang(at)gmail(dot)com> |
| Cc: | Andrei Lepikhov <lepihov(at)gmail(dot)com>, exclusion(at)gmail(dot)com, pgsql-bugs(at)lists(dot)postgresql(dot)org, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Subject: | Re: BUG #18652: Planner can not find pathkey item to sort for query with expression and expression index |
| Date: | 2024-10-10 10:20:36 |
| Message-ID: | CAMbWs4-tqttBrw5nOtQ0e=PPW5nO-k9gSk6MmNkfbfZfGph-vg@mail.gmail.com |
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| Lists: | pgsql-bugs |
On Thu, Oct 10, 2024 at 5:02 PM Tender Wang <tndrwang(at)gmail(dot)com> wrote:
> Andrei Lepikhov <lepihov(at)gmail(dot)com> 于2024年10月10日周四 14:50写道：
>> Looking into that case, I don't understand only one thing:
>> generate_orderedappend_paths decided to try MergeAppend; the
>> create_append_path routine added the Sort cost, but the Sort node
>> itself wasn't added. Maybe the origin problem is the lack of feasibility
>> examinations?
> Yeah, I'm also curious why only cost Sort but not adding Sort node in create_merge_append_path().
> The comments say that " We'll need to insert a Sort node, so include cost for that". Does another place
> insert the Sort node?
The Sort node will be added in createplan.c. This isn't exclusive to
MergeAppend; we also do so for MergeJoin, for example.
Thanks
Richard
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