Hello,
I am using Postgresql with PostGis and the Minnesota MapServer on a Beowulf cluster for web-mapping applications. It runs fine on one node, producing very fast interactive maps for an Apache/PHP web server. However, the cluster consists of 45 nodes, all using a shared user file system. Is it possible to start up a postmaster on every node, using the same database? The backend processes themselves would be completely autonomous, but they would have to share their data from the same source. To simplify things, only read-access is necessary. Would this be possible, and if so, how can the different postmasters be made to use a different postmaster.pid file (which is located in the shared data directory)?
It would be an interesting way for using the cluster, as the individual map layers can be independently constructed on different nodes, and only finally have to be put together in a complete map. Essentially, MapServer constructs a map from layers, where each layer originates from an individual PostgreSQL connection, even when using only one database. In a cluster solution therefore, no communication between the nodes would be required. Even the data could be distributed over the nodes and put into different databases, but this would inevitably lead to much duplication and a set of databases that would be very difficult to administer. In the archives, I saw some mention of work in progress on distributed databases, but for this I don't need much in the way of distributed facilities, just reading shared data.
Any help would be very much appreciated. It certainly would be a great example of PostgrSQL's advanced geometrical capabilities!
Jan Hartmann
Department of Geography
University of Amsterdam