From: | "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com> |
---|---|
To: | Josh Berkus <josh(at)agliodbs(dot)com> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: No heap lookups on index |
Date: | 2006-01-19 20:03:17 |
Message-ID: | 20060119200317.GY78403@pervasive.com |
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Lists: | pgsql-general pgsql-hackers |
On Thu, Jan 19, 2006 at 10:19:01AM -0800, Josh Berkus wrote:
> One of the other most valuable targets for index-only access is the
> "many-to-many join table" whose primary key consists of two (or more)
> foreign keys to two (or more) other tables. It's actually not necessary
> to check visibility on this kind of table as the visibility of tuples in
> the join table will be determined by the visibility of tuples in the two
> data tables. Since often join tables consist *only* of the join key,
> being able to do index-only access on them could dramatically speed up
> certian kinds of queries.
How would that handle 'delinking' item A from foobaz 2? (IE: DELETE FROM
join_table WHERE id1=231 and id2=24842)
The only way I can see this working is if it is required that items in
both tables as well as the link in the many-many table are only inserted
and deleted in the same transaction, which seems to be really pushing
this into corner-case territory.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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