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* Index containing records instead of pointers to the data?
@ 2011-09-18 20:18 Stefan Keller <sfkeller@gmail.com>
2011-09-18 20:21 ` Re: Index containing records instead of pointers to the data? Thom Brown <thom@linux.com>
2011-09-19 01:15 ` Re: Index containing records instead of pointers to the data? Craig James <craig_james@emolecules.com>
0 siblings, 2 replies; 3+ messages in thread
From: Stefan Keller @ 2011-09-18 20:18 UTC (permalink / raw)
To: pgsql-performance
Hi,
Sorry if this is an odd question:
I assume that Postgres indexes don't store records but only pointers
to the data.
This means, that there is always an additional access needed (real table I/O).
Would an index containing data records make sense?
Stefan
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Index containing records instead of pointers to the data?
2011-09-18 20:18 Index containing records instead of pointers to the data? Stefan Keller <sfkeller@gmail.com>
@ 2011-09-18 20:21 ` Thom Brown <thom@linux.com>
1 sibling, 0 replies; 3+ messages in thread
From: Thom Brown @ 2011-09-18 20:21 UTC (permalink / raw)
To: Stefan Keller <sfkeller@gmail.com>; +Cc: pgsql-performance
On 18 September 2011 21:18, Stefan Keller <sfkeller@gmail.com> wrote:
> Hi,
>
> Sorry if this is an odd question:
> I assume that Postgres indexes don't store records but only pointers
> to the data.
> This means, that there is always an additional access needed (real table I/O).
> Would an index containing data records make sense?
Yes, it's called a covering index, where the data required to produce
results for the query are entirely contained in the index. That
should be hopefully coming in 9.2.
See http://wiki.postgresql.org/wiki/Index-only_scans
--
Thom Brown
Twitter: @darkixion
IRC (freenode): dark_ixion
Registered Linux user: #516935
EnterpriseDB UK: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Index containing records instead of pointers to the data?
2011-09-18 20:18 Index containing records instead of pointers to the data? Stefan Keller <sfkeller@gmail.com>
@ 2011-09-19 01:15 ` Craig James <craig_james@emolecules.com>
1 sibling, 0 replies; 3+ messages in thread
From: Craig James @ 2011-09-19 01:15 UTC (permalink / raw)
To: pgsql-performance
On 9/18/11 1:18 PM, Stefan Keller wrote:
> Hi,
>
> Sorry if this is an odd question:
> I assume that Postgres indexes don't store records but only pointers
> to the data.
> This means, that there is always an additional access needed (real table I/O).
> Would an index containing data records make sense?
See my post entitled, "How to make hash indexes fast" for a solution to the additional-disk-access problem.
Craig
>
> Stefan
>
^ permalink raw reply [nested|flat] 3+ messages in thread
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2011-09-18 20:18 Index containing records instead of pointers to the data? Stefan Keller <sfkeller@gmail.com>
2011-09-18 20:21 ` Thom Brown <thom@linux.com>
2011-09-19 01:15 ` Craig James <craig_james@emolecules.com>
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