ArcGIS Explorer Blog : Cache

Your Cache Portfolio - Part 2

ArcGIS-Explorer-Team — Sat, 08 Nov 2008 00:15:00 GMT

In Part 1 of our mini-series on cache, we covered its implications with the default map and using other maps and layers from the Resource Center. Here in Part 2 we'll take a closer look at managing cache when connecting to individual services and local data.

ArcGIS Explorer either fetches cache (when leveraging cache or cache-on-demand capabilities in ArcGIS Server) or creates it when you first connect to content. This happens whether it's an internet service or local data. This results in optimized performance, and also enables offline use. But there may be times when we don't want to create cache, or when we might want to update it at regular intervals. For example, when we connect to a weather service that is continually updating.

When you add content to ArcGIS Explorer you go through a wizard, and will eventually see the Disk Caching Options dialog (except when you connect to GeoRSS feeds, or add KML or KMZ, which don't use this option).

Let's examine the options more closely.

Save layer's disk cache when saving map file.

This option is the default, and is appropriate for any non-dynamic content source. This will ensure that cache that is fetched or created during your session is saved locally when you save your map. The next time you open the map, you won't have to fetch or create cache again; it will be read directly from your local cache saved to disk.

Create a disk cache for the layer during the session.

Cache will be created as you work with your map during your session, but won't be saved. This is appropriate for content you know will change, but aren't sure how often it may be updated. It can be augmneted by choosing a time interval for refreshing the cache, discussed below.

Don't create a cache for the layer on disk.

Cache won't be saved at all, but this means that it will be continuously fetched or created.

A good option to use is the time interval option which clears all layer cache at the specified interval. This is optimal for most dynamic content like weather. We can set an update, say every 15 minutes, and cache will be cleared and refreshed at the specified interval. When the map is saved and reopened, the layer will automically refresh its cache and then updated at the specified interval.

Using these choices you can ensure you've got both the best performance and are viewing the most up-to-date content.

Another way you can refresh cache is manually by using the Layer Manager (Tools > Manage Layers).

Highlight the layer and click Clear Layer Cache to remove all cache for that layer.

And a final way to remove cache is via Tools > Options > Cache > Disk Cache. Choosing All Caches and clicking Delete Caches will clear all your local ArcGIS Explorer cache. We covered this at the end of our previous post.

Your Cache Portfolio - Part 1

ArcGIS-Explorer-Team — Thu, 06 Nov 2008 01:30:00 GMT

You should see your investment advisor about investing cash, but in this two part post we'll cover how you can best manage your investment in Explorer map cache. Under most circumstances cache and how it is managed are completely internal to the application. But knowing a little more about it will help you make the right decisions about managing your own cache, and in making decisions about how you connect to services.

We'll begin by covering the implications of cache as it pertains to the default map, and other maps and layers you can access from the Content tab on the Explorer Resource Center.

Behind the scenes the default map and other maps are powered by ArcGIS Online, a large repository of online content and services that can be used in ArcGIS Explorer, ArcGIS Desktop, and ArcGIS Server. The ArcGIS Online services are powered by ArcGIS Server, and use ArcGIS Server's caching capabilities to streamline performance, and reduce client/server overhead. The ArcGIS Server 9.3 Help describes caching as follows:

Map caching is a very effective way to make your ArcGIS Server maps run faster. When you create a map cache, the server draws the entire map at several different scales, and stores copies of the map images. The server can then distribute these images whenever someone asks for a map. It's much quicker for ArcGIS Server to hand out a cached image than to draw the map each time someone requests it. Another benefit of caching is that the amount of detail in the image doesn't noticeably affect how quickly the server can distribute the copy.

The bottom line is that caching is a feature of ArcGIS Server that makes things better for you - the ArcGIS Explorer user.

When you first connect to a service you communicate with the ArcGIS Online's ArcGIS Servers. Cache is "handed out" to Explorer, and you'll see the Streaming... progress bar at the bottom of the map.

What's happening is that cache is being transferred from the ArcGIS Online servers to Explorer, where it's stored locally. This is somewhat similar to how bits and pieces of internet sites you visit are stored in browser cache to optimize performance when visiting the site again.

Once local, the next time you visit the same location Explorer doesn't even have to communicate with the server. It knows that it already has the cache it needs and simply uses it from local storage, resulting in best performance and minimizing client/server communications.

In an earlier post we blogged about how Explorer's default startup map and other layers you find on the Resource Center are regularly updated. To see these updates in areas that you've already visited you will have delete your local cache since Explorer knows you've already been there, and doesn't fetch new cache from the server.

But now that we said that, it's not entirely accurate. There were many changes in ArcGIS Online services in recent months that were automatically propagated to all Explorer users. That happened since we changed the ArcGIS Online server URL string to indicate a migration from the 9.2 version of ArcGIS Server to the 9.3 version. As a result of that change, new cache was pushed out automatically. But unless ESRI does something on the back end, some changes may be made to ArcGIS Online services that you'll need to refresh your cache to see.

To refresh your cache, just go to Tools > Options > Cache and choose Disk Cache. Check the option for All Caches and click Delete Caches.

It's a good idea to periodically refresh your cache, and good practice to make it part of your housekeeping activities.

In Part II, we'll cover how to have your cache refresh automatically when connecting to services.

Using Dynamic Content

ArcGIS-Explorer-Team — Thu, 24 Jan 2008 18:22:00 GMT

ArcGIS Explorer 440 includes enhancements which make it easier to use and manage dynamic layer content from services that are continually being updated, like weather or active fire perimeters.

When you connect to one of these services you have full control over the refresh interval, and with Explorer 440 the cache for dynamic layers is automatically refreshed on open, so you'll always have the latest information. This now applies to all content sources, including both 2D and 3D services published via ArcGIS Server, 2D services published via ArcIMS, or local vector and raster data.

In this example we're going to use a weather service provided by Meteorlogix, one of ESRI's business partners. The Meteorlogix weather information service that ESRI taps into provides updated information every 15 minutes, and the data is being manipulated and stored in an Oracle-based enterprise geodatabase. As part of the geodatabase input process the data is generalized somewhat (for performance) and cell-based information is aggregated into polygons. As the data is refreshed in the geodatabase it is also being date-stamped, so that historical weather trends can be analyzed using ArcGIS Desktop's Tracking Analyst.

In ArcGIS Explorer we're interested in adding this service as a dynamic layer which refreshes automatically. To do this, we connect to the service in Explorer by choosing File, then Open, and selecting Server as the content type we wish to open.

Below we've clicked ArcGIS Server from the Create New Connection choices along the top, and have provided the necessary connection information to connect to the ESRI internal server that is publishing the weather (sorry, we don't yet publish weather as a publicly accessible service).

Now that we've established a connection to the server, we can scroll down and see the list of published services that are available. Below we've chosen to connect to the Meteorlogix weather service that we described above.

Now that we've chosen the weather service, we're guided by a wizard to specify certain parameters. Note that there is a user option to remember what we've specified the next time around.

First we're asked to specify the raster cell size, for which we accept the default chosen by Explorer. Next we're asked to choose from among the sublayers published in this service. And now to the important part - we're asked to specify the disk caching options. Since the weather data is updated on the server every 15 minutes, we'll choose the option for "Don't create a cache for the layer on disk." This also enables the choice for refreshing cache based on a time interval, and we'll specify 15 minutes as the refresh rate.

Using these settings Explorer will communicate with the server and refresh cache for this layer every 15 minutes. If the map is saved, when opened again it will automatically refresh the layer, then refresh at the specified 15 minute interval, ensuring that what you see is up to date.

You can experiment with this yourself using any service or local data source. For a detailed discussion on cache and various cache management options, refer to the Cache management in ArcGIS Explorer Help topic.

Updates to ArcGIS Explorer's Services = Cache Cleaning Time

ArcGIS-Explorer-Team — Thu, 20 Dec 2007 19:03:00 GMT

Just prior to this latest release a couple of the ArcGIS Online services which deliver content in several of the maps and layers available through the Contents tab on the Explorer Resource Center were updated. These changes include the following:

World Shaded Relief: added additional levels of detail
Physical World: added additional levels of detail, plus bathymetry at small scales

An ArcGIS Online Forum post also covers these changes, with a few additional details.

To view these updates, you'll have to clear your cache for these layers. To do so, choose Tools, Manage Layers, and then select the layers above (if you are using them in your map) and click the Clear Layer Cache button.

If you don't use these layers regularly, but want to make sure you've cleared their cache to see the updates, you can take your cache housekeeping a little further and delete all of your cache, and start afresh. This isn't required, but you might want to do this from time to time just as a regular housekeeping task.

Remember that if you do clear all your cache, you'll be fetching fresh cache from ESRI's servers, as well as from any other servers that you may connect to, and generating new cache for your local data sources. Your performance will be a little slower while you fetch or generate cache again.

To clear out your cache, choose Tools, then Options, and choose Cache in the options list. Click *** Cache, and under Cache Clean Up choose All Caches before clicking the Delete Caches button.

See the Help topic Cache Management in ArcGIS Explorer for additional details, and more information.

There will be other service updates during Q1 next year, and we'll keep you posted as to when they'll be happening.