For the fastest performance of your ArcGIS Server map services, we recommend
that you use
map caching wherever it’s appropriate. A map cache is a picture of your
map at one point in time. Map caches are obviously appropriate for maps that
don’t change frequently, such as street maps and imagery. But thanks to the
update tools included with ArcGIS Server, you may still be able to use caching
even if your data changes more often.
The Update Map Server Cache geoprocessing tool helps you update an existing map cache. You can
write a script that uses this tool, then schedule the update to run on a
regular basis. Even if you’ve never written a script or scheduled a task
before, it’s worth the effort to learn how because of the performance
improvements you can get from using a cached map. This post walks you through
Deciding if you should cache your changing data
To understand whether your frequently-changing map can still be cached, it helps
to ask these questions:
How up-to-date does my map need to be?
If the data you see on the map needs to be live, with no time delay acceptable,
then caching is not appropriate. However, if a short delay is acceptable and
the cache updates can be performed within that time window, you can still use
How big is my cache?
A larger cache takes more time to update. But if you can isolate the areas of
change, you may be able to shorten the update time.
For example, Jeremy Bartley wrote
a script that updates areas based on feature extents, instead of
updating the entire cache. If you’re editing data in national parks, but you
need a map of the entire country, you use this script to update your cache in
the national parks only. This can save an enormous amount of time and server
When you use this script, remember that if data and symbology are frequently
changing throughout your map, the update will take longer than if the changes
were confined to a few specific areas.
To summarize, if the update can keep up with the changes in an acceptable amount
of time, the map is appropriate for caching.
The following scenarios might give you an idea of what types of maps are
appropriate or inappropriate for caching.
National and regional weather maps
Probably appropriate for caching. A map viewed at a national or regional scale
does not require many tiles and can be updated before the weather drastically
Cadastral maps of a city that change on a daily basis
Probably appropriate for caching because a city is not a large area and the
cache can run overnight. However if no delay is acceptable, the map might not
be appropriate for caching.
Maps that update vehicle or ship positions every 10 minutes
May be appropriate if the cache can be updated in less than 10 minutes. This
depends on the size of the map, the cache scales, and available server
Maps for 911 dispatchers that display incidents and responders in real time
Probably not appropriate for caching because no time delay is
Preparing to write the script
When you initially create the map cache, note how long it takes. This will give
you an idea of how long it would take to update the entire cache.
After the cache generation tool runs, you may want to copy the text from the
geoprocessing message box and paste it into Notepad. This isn’t required; it’s
just for convenience when writing your update script. You can copy and paste
some of the parameters from the message box into your script.
Writing a script to update your cache
To automate cache updates, you can create a Python script that runs the Update
Map Server Cache tool. You can write the Python inside of Notepad, or you can
use a development environment such as IDLE or PythonWin.
The script does not have to be complex. It just needs to define the parameters
for the tool and run it. The following Python script runs the Update Map Server
Cache tool to re-create an entire cache:
# This script updates all tiles in an ArcGIS Server 9.2 map cache
# Access the geoprocessing tools
gp = arcgisscripting.create()
# Set up all of the variables for the update tool
server_name = "myserver1"
object_name = "Precipitation"
data_frame = "Layers"
layers = ""
constraining_extent = ""
scales = "32000000;16000000;8000000;4000000;2000000"
update_mode = "Recreate All Tiles"
thread_count = "2"
antialiasing = "NONE"
# Run the Update Map Server Cache tool
print 'Starting Cache Update'
gp.UpdateMapServerCache(server_name, object_name, data_frame, layers, constraining_extent, scales, update_mode, thread_count, antialiasing)
print 'Finished Cache Update'
# Get the error messages if the tool fails
If you’re just getting started with scripting you can just copy the above into
Notepad, substitute your own variables, and save it with a .py extension. If
you need help understanding the variables, see the
Geoprocessing tool reference for Update Map Server Cache.
Scheduling the update to run automatically
Once you’ve saved your Python script, you can run it on any machine that has ArcGIS Server and Python installed by double-clicking the .py file in Windows Explorer. (Python
is included with ArcGIS Desktop so you may already have it installed. Otherwise
visit www.python.org to get Python.)
Running the script manually in this way can be useful for testing, but in most
cases you’ll want to schedule the script to run on a regular basis.
Your operating system contains utilities that help you schedule tasks such as
running a script. You’ll need to provide the location of the script file, how
often you want it to run, and the name and password that the task will run as.
Scheduled Task Wizard in Windows walks you through the process of
setting up the task. Open the wizard by clicking Start > All Programs >
Accessories > System Tools > Scheduled Tasks > Add Scheduled Task.
If you want a few more options than the wizard provides, you can schedule the
task from the command prompt. Just open Start > All Programs >
Accessories > Command Prompt and enter your command: like the following,
which schedules a Python script to run every 30 minutes:
schtasks /create /sc minute /mo 30 /tn "Update My Cache" /tr C:92CachingScriptsUpdate.py
If you need help creating a command like this, see the
Microsoft documentation for the schtasks command.
Dedicating server resources to the update
At this point you may wonder if your server can handle the cache updates and
fill user requests at the same time. Updating a cache definitely uses server
resources because the server is required to continually draw map tiles during
the update. However, the update doesn’t have to tie up your entire server.
Each service has a maximum number of instances of the service that are allowed
to run, which you can adjust in the Service Properties. You can also use the
caching tools to specify how many of those instances will be dedicated to
caching (this is the “thread_count” variable in the script above). If you’re
short on server resources, you can lower the number of instances dedicated to
caching so that others can continue to use your service while the update
In summary, if you want others to continue using your service while you are
updating, make sure that the number of instances dedicated to caching is less
than the maximum allowable number of instances.
It’s also important to note that running Update Map Server Cache forces two
restarts of the service – once before the update starts and once after the
update finishes. Your services may be momentarily unavailable during the
Scheduling your update to run on nights or weekends can also lessen the chance
of the update interfering with regular server traffic. Many organizations have
nightly backup or update processes, into which you could incorporate your cache