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Re: pgsql: Support RIGHT and FULL OUTER JOIN in hash joins.

From: Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-committers(at)postgresql(dot)org
Subject: Re: pgsql: Support RIGHT and FULL OUTER JOIN in hash joins.
Date: 2011-05-25 02:01:46
Message-ID: BANLkTi=vAGgYAS21zu0kv1SsfmvTkDbRMg@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-committers
2011/5/24 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> Hitoshi Harada <umi(dot)tanuki(at)gmail(dot)com> writes:
>> It looks to me like mergejoin_allowed should be initialized to false.
>> If enable_mergejoin is off and jointype != JOIN_FULL then mergejoin is
>> not allowed, isn't it? Sorry for noise if it's only my confusing.
>
> No, the code is correct as-is: we need the flag to be set true by
> default, because the way that the function is using it, we'll also skip
> some nestloop possibilities when it's false.  Note the comment for step
> 2.
>
> It could be that a different name for that flag variable would be a
> better idea, but neither Robert nor I could come up with a better one.

Ah, ok. I think I now understand it. "mergejoin_doable" flag. Thanks.

Regards,


-- 
Hitoshi Harada

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