| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Josh Berkus <josh(at)agliodbs(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Ants Aasma <ants(at)cybertec(dot)at>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Why is indexonlyscan so darned slow? |
| Date: | 2012-05-21 20:37:06 |
| Message-ID: | CA+U5nM+gf5F=nm3ceaiWofXS+rjybUn_vsLRQakOp+0byGDn4A@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 21 May 2012 16:02, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>> Surely the way to solve this is by having a new plan node that does a
>> physical SeqScan of the index relation. It means we wouldn't preserve
>> the sort order of the rows from the index, but that is just a plan
>> cost issue.
>
>> This is exactly what we do for VACUUM and it works faster there.
>
> The reason that's okay for vacuum is that vacuum doesn't care if it
> visits the same index tuple multiple times. It will not work for real
> queries, unless you would like to lock out all concurrent inserts.
I checked a little more and Oracle supports something called a Fast
Index Scan. Maybe there is a way.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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