Re: Index only scan

Thanks all for the help and insights. I will continue to read up on
the details of partitioning and pgpool.

best regards,

Lars

On Thu, Oct 11, 2012 at 2:47 AM, Gavin Flower
<GavinFlower(at)archidevsys(dot)co(dot)nz> wrote:
> On 11/10/12 12:41, Tom Lane wrote:
>>
>> Gavin Flower <GavinFlower(at)archidevsys(dot)co(dot)nz> writes:
>>>
>>> On 11/10/12 01:03, Lars Helge Øverland wrote:
>>>>
>>>> My question is: Would it be feasible and/or possible to implement
>>>> index only scans in a way that it could take advantage of several,
>>>> single-column indexes? For example, a query spanning columns a, b, c
>>>> could take advantage of 3 single-column indexes put on columns a, b,
>>>> c.
>>>
>>> Index only scans do use multiple indexes of single fields where
>>> appropriate. Here the planner determined it only needed to scan 2 of
>>> the 3 relevant single field indexes.
>>
>> But your example isn't an index-only scan ... it's a plain old bitmap
>> scan, and so it does touch the heap.
>>
>> The difficulty with what Lars proposes is that there's no way to scan
>> the different indexes "in sync" --- each one will be ordered according
>> to its own column order. In principle I guess we could read out the
>> index data and do a join using the ctid's, but it's far from clear that
>> such a thing would be worth the trouble.
>>
>> regards, tom lane
>
> Thanks for the correction!
>
> Cheers,
> Gavin