[postgis-users] Re: [PERFORM] Bad query optimizer misestimation because of TOAST

[Markus Schaber]

Hi, Strk,

strk at refractions.net schrieb:

> PostGIS always recheck, only to handle SRID consistency.
> This is one of the problems Paul was ranting about in a previous
> post ;). If no RECHECK is performed, queries using index
> will not notice SRID mismatch, while those using a sequencial
> scan will.

Was this the case for 0.X PostGIS, too?

> I wonder if dropping the RECHECK is another workaround for your
> problem. Can you check it out ?

No. The problem was that the query planner was not using the index at
all, thus forcing the load of all geometries during the sequential scan.

The lossiness of the index usually only causes very few false positives
that have to be loaded for recheck, so I would regard this as a minor
problem.

Markus


--
markus schaber | dipl. informatiker
logi-track ag | rennweg 14-16 | ch 8001 zürich
phone +41-43-888 62 52 | fax +41-43-888 62 53
mailto:schabios at logi-track.com | www.logi-track.com

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