[Qgis-developer] Benchmarking QgsExpression against V8

[Martin Dobias]

On Tue, Jan 10, 2012 at 5:02 PM, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> wrote:
> Hi Martin
>
>
>>- it may be interesting to measure the proportion of time necessary
>>for field calculation / searching. I believe the the evaluation takes
>>just a small amount of time compared to time required for fetching of
>>features, therefore a fast engine might not necessarily speed things
>>up significantly
>
> That would be very interesting (probably it can be tested much better now
> thanks to qgis_bench).
>
> My only experience here was the WMS benchmark 2011 with many layers and a
> lot of expressions (osm data, a lot of classification rules, many layers).
> For requests with a lot of features in view, expression evaluation showed up
> considerably in the profiler, both in QGIS server and UMN mapserver. Yes,
> feature fetching wasn't considered (still cachegrind) and I don't have the
> cachegrind dumps at hand. However, it still shows that there are use-cases
> where evaluation is not neglectable.

Hi Marco

which implementation of expressions has been used in the benchmark -
the old one (search strings) or the new one? If you have some saved
callgrind dumps, I could have a look whether there are any issues that
could be optimized easily. If there are serious speed problems, then
we could start considering a better performing engine. Anyway as I
written in my earlier mail, there may be issues with with supporting
3-value logic.

Regards
Martin