Strategies for large caching jobs
ArcGIS Server 9.2 introduced map caching for map services. A cached map service is a regular map service that has been enhanced to serve maps very quickly using a cache of static images. The map cache is a directory that contains image tiles of a map extent at specific scales. Map caching greatly improves the performance of a map service, allowing clients to directly retrieve tiles from the cache rather than having the server dynamically generate the map images.
Most caching jobs are relatively straightforward and can be completed in a few hours (e.g., city, county, or other small areas). However, larger caching jobs (e.g., entire countries or the world cached to large scales) can take days to complete. Thus, it’s a good idea to have an overall strategy so you don’t waste your time building a cache only to find that it doesn’t suit your needs. Keep in mind that caching is an investment. The time you spend now building your cache will be time saved by the people who use it.
As with all caching jobs, you need to answer some questions beforehand. Some questions relate specifically to the cache, for example, what scales do you want to use? Do you need to cache all your data at all scales or can you cache specific areas of interest (e.g., only train yards, National Parks, or major metropolitan areas)? Other questions deal with your hardware environment, for example, do you have enough disk space? Do you have enough resources to complete the job in a timely manner? Instead, let’s take a look at a best practice for building large caches.