I am a new QGIS user and I am curious about how slowly it is performing; it is possible that I'm asking more of it than I think I am. Here's what I think is the relevant information for assessing whether it's performance is unusually slow.
QGIS version 1.74 GDAL/OGR version 1.9.0 PostgreSQL client version 9.1.2 QWT version 4.8.0
Project info: 1 vector layer of polygons queried from a remote PostGIS database (query is simple and very fast) returning 160 total rows all in the project's defined coordinate space (WGS 84) and spanning the globe. The PostgreSQL table containing those rows occupies less than 130 kb of disk space, and the queried rows comprise pretty much the entire table.
System: MacBook OS X 10.7.3, 2.4GHz Intel Core Duo, 4GB RAM.
Performance: Rendering takes 5-10 minutes. In fact, any change takes nearly that long, including renaming the single layer; that really surprised me. No other memory-hungry applications are running concurrently.
This is frustrating because any modification of the project, however slight, requires a lengthy wait before the results can be assessed, and sometimes the application simply crashes without completing whatever I asked. Is this unusual?
I have Shapefiles of the same data. They are 45 files totaling about 100 MB. That figure is clearly discrepant with the size of the data set I described in my original post and it makes the slowness more understandable.
I just discovered the "Render" button at the bottom left of the QGIS map viewer. I feel like a bit of an idiot for not having noticed it before, but turning off rendering greatly increases the speed with which I can accomplish tasks for which immediate re-rendering isn't critical. I mention this here for the benefit of other new users.