[Qgis-developer] QGIS Server does not release files after each request - OGROpenShared instead of OGROpen ?

[kimaidou]

Hi all

We are trying to use QGIS Server with nginx / supervisor instead of
classical Apache / mod_fcgid.

We have seen that for each server request, such as a GetMap responding an
image rendered from a single Shapefile (or Tiff, of whatever), QGIS Server
opens a new access to the file.

Exemple number found via the lsof command, after some requests

lsof /tmp/someShapefile.shp | wc -l
126

which means here 126 requests has been processed by QGIS Server, but the
access to Shapfile has never been released. Each requests leads to a new
file handler.

Imagine a project with several layers, and a web map with many users /
requests --> this lead rapidly to many opening of the same files open for
nothing, and can cause issues.

In Apache configuration, this was not sensible, as mod_fcgid and Apache
kill QGIS Server worker after N completed requests, and it seems the ulimit
used is the system limit.

In our configuration, supervisor has by default a ulimit of 1024 files
opened. This limit is vers fast reached ( 1024 requests only ). We could
tune this configuration, but it seems to walk aournd the issue without
solving its origin.


We have 2 ways of dealing with it :

* Make sure QGIS Server does not open a data file each time a request needs
it --> we will investigate if the cache is well used

* We could also use GDALOpenShared instead of GDALOpen , and OGROpenShared
instead of OGROpen in QGIS provider code:

GDALOpenShared :
http://www.gdal.org/gdal_8h.html#a46a02c21047d78f88f8abb1ff6b14ae2
OGROpen in QGIS :
https://github.com/qgis/QGIS/search?utf8=%E2%9C%93&q=ogropen&type=Code


Any idea, comment appreciated !

Regards,
Michaël
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-developer/attachments/20150911/d01cd8e0/attachment.html>