[gdal-dev] PgSQL and OLCFastFeatureCount

[Even Rouault]

Selon Paul Ramsey <pramsey at cleverelephant.ca>:

> The PgSQL driver is returning TRUE for OLCFastFeatureCount and then running
> "SELECT Count(*)” to fulfill the request. Since that is actually going to
> apply a full table scan, it’s not *really* a fast feature count in my
> estimation, but perhaps GDAL has a different standard? What’s the standard
> for a fast feature count? Basically instant (the record count resides in
> header metadata or something similar)? Or “fast enough for small things”?

Paul,

The standard for "fast" is not well defined I think. Instant would be ideal, but
a number of drivers advertize FastFeatureCount when they have a specialized
implementation that is faster than the generic one. In that instance the request
is run entirely on server side, so this is much faster than the default
implementation. It is a bit surprising that PostgreSQL cannot maintain the
feature count without going to a full table scan, but I guess there are
technical difficulties related to concurrent updates to do so.

Even

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