Tom Lane wrote:
> Heikki Linnakangas <[EMAIL PROTECTED]> writes:
> > For the record, this patch has a small negative impact on scans like 
> > "SELECT * FROM foo LIMIT 1000". If such a scan is run repeatedly, in CVS 
> > HEAD the first 1000 rows will stay in buffer cache, but with the patch 
> > each scan will start from roughly where previous one stopped, requiring 
> > more pages to be read from disk each time. I don't think it's something 
> > to worry about in practice, but I thought I'd mention it.
> Urgh.  The answers change depending on (more or less) the phase of the
> moon?  I've got a serious problem with that.  You might look back to
> 1997 when GEQO very nearly got tossed out entirely because it destroyed
> reproducibility of query results.

What about the simple idea of just disabling the use of a sync scan when
the query has LIMIT and no ORDER BY, and start always at block 0 in that

Alvaro Herrera                      
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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