Cache Configuration

Caching results can improve the performance of an application and reduce the server load a lot. Please note the difference between server-side and client-side caching, both of which are described below.

Server-side Tile Caching

Map tiles can be cached on the server side, instead of redrawing the tiles for every request. There are multiple proxy and cache technologies and products available. Because of ist simple configuration and its great spread, we describe a tile cache implementation based on the nginx HTTP server.

Prerequisites

Download the latest nginx version and install it.

Configuration

• Change the nginx configuration file nginx.conf to the following content:

  
  events {
      worker_connections  1024;
  }
  
  http {
      
      #configure location and size of the cache
      proxy_cache_path /opt/xserver-tile-cache levels=1:2 keys_zone=one:10m max_size=5g;
      proxy_temp_path /opt/xserver-tile-cache/tmp;
  
      #define a exclusion rule for dynamic map data like PTV_TrafficIncidents
      map $arg_layers $ignore_cache {
          default 0;
          ~(.*)PTV_TrafficIncidents(.*) 1;
      }
      
      server {
          
          #public port of the cache/xserver proxy
          listen 80;
    
          #location definition for all xmap rest requests
          location /services/rest/XMap/ {
              
              #cache configuration
              expires 24h;
              proxy_cache_bypass $ignore_cache;
              proxy_no_cache $ignore_cache;
              proxy_cache one;
              proxy_ignore_headers Cache-Control;
              proxy_cache_valid any 24h;
              
              proxy_pass http://localhost:50000;
          }
          
          #location definition for all other requests
          location / {
              
              #forward the requests to the xserver backend
              proxy_pass http://localhost:50000;
          }
      }
  }
          

• Adjust the paths, ports and URLs according to the local environment
• Start the nginx and xServer

Client-side Caching

Redundant requests can be served from the client's cache, which reduces the workload for the server. For the Map Tile API and Routing REST requests, the PTV xServer 2 can set HTTP response header directives accordingly.

Configuration

The HTTP response header directives set in the RESTREST (Representational State Transfer) represents a World Wide Web paradigm, consisting of constraints to the design of components which results in a better performance and maintainability. responses can be configured in the xserver.conf:

        core {
            [...]

            cacheControl {
                maximumAge = 86400
            }
        }
    

By default, the maximum age for cached responses on client-side is set to 24h.

With the default settings shown above, the cache header of the response to the xMap tile request http://hostname:50000/services/rest/XMap/tile/13/4238/2790 is valid for 24 hours:

            cache-control: public, max-age=86400
            content-length: 7705
            content-type: image/png
            [...]
        

On the other hand, xMap and xRoute REST requests with

• the FeatureLayer "PTV_TrafficIncidents" (e.g. http://hostname:50000/services/rest/XMap/tile/13/4235/2792?layers=PTV_TrafficIncidents) or
• one of the following TimeConsiderationScenarios and no specified ReferenceTime (which defaults to the current UTC time, e.g. http://hostname:50000/services/rest/XRoute/routeA route corresponds to a path of a vehicle through the underlying transport network. The main attributes of a route are the distance and the time that the vehicle travels along the path./6.12/49.58/6.12/49.58?timeConsideration=SNAPSHOT):
  • SNAPSHOT
  • TIME_SPAN
  • EXACT_TIME_AT_START
  • EXACT_TIME_AT_ARRIVAL

may have dynamically changing data and therefore will not be cached:

            cache-control: no-cache, no-store, must-revalidate
            content-length: 1615
            content-type: image/png
            [...]