| From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
|---|---|
| To: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com>, PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Index scan optimization |
| Date: | 2014-09-25 14:31:00 |
| Message-ID: | CA+U5nMJJnLgUS1Vw-sfnJ7=AJJTe5vK_OR+WMow=eUU+1KHW4w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On 22 September 2014 14:46, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> wrote:
> On 09/22/2014 04:45 PM, Tom Lane wrote:
>>
>> Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> writes:
>>>
>>> On 09/22/2014 07:47 AM, Rajeev rastogi wrote:
>>>>
>>>> So my proposal is to skip the condition check on the first scan key
>>>> condition for every tuple.
>>
>>
>>> The same happens in a single-column case. If you have a query like
>>> "SELECT * FROM tbl2 where id2 > 'a'", once you've found the start
>>> position of the scan, you know that all the rows that follow match too.
>>
>>
>> ... unless you're doing a backwards scan.
>
>
> Sure. And you have to still check for NULLs. Have to get the details right..
And also that the tests don't use volatile functions.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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