From: | Richard Guo <guofenglinux(at)gmail(dot)com> |
---|---|
To: | PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Support "Right Semi Join" plan shapes |
Date: | 2023-08-10 07:24:28 |
Message-ID: | CAMbWs4_ccjTJSksy5Z_WxmhoxO5n2PZ49qSQHaXb2JxzKZ=x8g@mail.gmail.com |
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Lists: | pgsql-hackers |
On Tue, Apr 18, 2023 at 5:07 PM Richard Guo <guofenglinux(at)gmail(dot)com> wrote:
> In thread [1] which discussed 'Right Anti Join', Tom once mentioned
> 'Right Semi Join'. After a preliminary investigation I think it is
> beneficial and can be implemented with very short change. With 'Right
> Semi Join', what we want to do is to just have the first match for each
> inner tuple. For HashJoin, after scanning the hash bucket for matches
> to current outer, we just need to check whether the inner tuple has been
> set match and skip it if so. For MergeJoin, we can do it by avoiding
> restoring inner scan to the marked tuple in EXEC_MJ_TESTOUTER, in the
> case when new outer tuple == marked tuple.
>
> As that thread is already too long, fork a new thread and attach a patch
> used for discussion. The patch implements 'Right Semi Join' for
> HashJoin.
>
The cfbot reminds that this patch does not apply any more, so rebase it
to v2.
Thanks
Richard
Attachment | Content-Type | Size |
---|---|---|
v2-0001-Support-Right-Semi-Join-plan-shapes.patch | application/octet-stream | 24.6 KB |
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