Re: Select performance vs. mssql

От: Jim C. Nasby
Тема: Re: Select performance vs. mssql
Дата: ,
Msg-id: 20050529163312.GK44623@decibel.org
(см: обсуждение, исходный текст)
Ответ на: Re: Select performance vs. mssql  (Christopher Kings-Lynne)
Список: pgsql-performance

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Select performance vs. mssql  (mark durrant, )
 Re: Select performance vs. mssql  (Christopher Kings-Lynne, )
 Re: Select performance vs. mssql  (mark durrant, )
  Re: Select performance vs. mssql  (Neil Conway, )
  Re: Select performance vs. mssql  ("Harald Lau (Sector-X)", )
 Re: Select performance vs. mssql  (mark durrant, )
  Re: Select performance vs. mssql  (Bruno Wolff III, )
   Re: Select performance vs. mssql  (Alex Turner, )
   Re: Select performance vs. mssql  (Enrico Weigelt, )
    Re: Select performance vs. mssql  (Jochem van Dieten, )
  Re: Select performance vs. mssql  (Christopher Kings-Lynne, )
   Re: Select performance vs. mssql  ("Jim C. Nasby", )
 Re: Select performance vs. mssql  (mark durrant, )
  Re: Select performance vs. mssql  (Josh Berkus, )
   Re: Select performance vs. mssql  (PFC, )
   Re: Select performance vs. mssql  (Michael Stone, )
    Re: Select performance vs. mssql  (John A Meinel, )

On Wed, May 25, 2005 at 09:29:36AM +0800, Christopher Kings-Lynne wrote:
> >--MSSQL's ability to hit the index only and not having
> >to go to the table itself results in a _big_
> >performance/efficiency gain. If someone who's in
> >development wants to pass this along, it would be a
> >nice addition to PostgreSQL sometime in the future.
> >I'd suspect that as well as making one query faster,
> >it would make everything else faster/more scalable as
> >the server load is so much less.
>
> This is well-known and many databases do it.  However, due to MVCC
> considerations in PostgreSQL, it's not feasible for us to implement it...

Wasn't there a plan to store some visibility info in indexes? IIRC the
idea was that a bit would be set in the index tuple indicating that all
transactions that wouldn't be able to see that index value were
complete, meaning that there was no reason to hit the heap for that
tuple.

I looked on the TODO but didn't see this, maybe it fell through the
cracks?
--
Jim C. Nasby, Database Consultant               
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