[Qgis-developer] Re: PostGIS provider estimated extent

[Jeremy Palmer]

Hi Jürgen,

> Yes.  That was the problem.  Trying to use estimates without actually having
> any caused the query to fail.  That also invalidates all open cursors.  The
> idea was that either all or no tables have estimates.   In the latter case the
> very first query would fail and subsequent queries wouldn't try to use
> estimates.

Sorry for the late reply!

The use of the estimated_extent function is very important for me as I'm dealing with large PostGIS datasets. The way the postgis provider is implemented at the moment prevents the use of estimated_extent once it has failed once. This means that after I have looked at a table that hasn't been analysed or is a view, then every other table on the same connection that I use after that is hopelessly slow, because it no longer uses the estimated extents function. The only way I can reset this is to restart Qgis.

I can understand that we need to rollback the transaction when the estimated extents function has failed, but I can't see a reason not to try to use it for other tables on the same connection.

Could I suggest we keep the rollback on the cursor if we get an error, but to still allow subsequent calls of the estimated_extent functions on the connection even after a failure?

I have attached a patch that implements my suggestion, and if you agree I will create a ticket :)

Kind regards,
Jeremy

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Thank you.
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