What's in a Name: When in_memory != In-memory
This is the second in a four-part series on the challenges of naming new features in software applications; particularly, the consequences when naming falls short. The first part in the series looks at a case when the name of a new feature clearly and succinctly describes the behavior of that feature. The second part in the series looks at that same case when newer yet functionality alters the original behavior of that new functionality. The third part in the series looks at how the documentation has changed to addresses this altered functionality. And finally, the fourth part in the series discusses what it all means to end users and developers.
When I first started beta testing ArcGIS 9.4, it didn't take long for me to see this was going to be a big release for Esri. It turns out, it was big enough to get promoted from a minor release to a major one during beta, and we all ended up with ArcGIS 10.0. The What's New in ArcGIS 10 covers lots of ground, there is just about something for everyone in there. No matter how narrow or limited your use of ArcGIS Desktop may be, one change you couldn't miss was the user interface, which had remained quite constant through the ArcGIS 8.x and 9.x days.
I was interested in lots of the changes with ArcGIS 10.0, so many I shouldn't even bother starting to list them here. Although lots of changes got my attention, the changes to geoprocessing really stood out: background processing was introduced, the Python window replaced the Command Line window, ArcPy took Python support to the next level, and more. Combining all of these new features with one of my favorite existing features, the in-memory workspace, I was actually a bit excited to kick the tires and see just how great this next ride might be.
Unlike ArcGIS 9.2 where I had to use the Wayback Data Center, ArcGIS 10.0 is still in production around parts of my agency, which makes it easy to take a step back in time and still generate new screenshots.
For the sake of consistency and simplicity, I will just re-use the examples from the first post in this series (What's in a Name: When in_memory = In-memory) to get acquainted with the Python window in ArcGIS 10.0. Let's take a look at the results of creating a table in the in-memory workspace:
Success, or not? The command appears to have completed successfully, but tmpTable doesn't appear to be in the GPInMemoryWorkspace. I am going to run that command again.
Huh. The command completed successfully; but again, the tmpTable doesn't appear to be in the GPInMemoryWorkspace. In fact, now I have two tmpTables, and each one seems to have its own cryptic geodatabase in my Temp folder. Unlike in ArcGIS 9.2 where the command failed because tmpTable already existed, ArcGIS 10.0 does you a favor, if you can call it that, by just creating another one in another cryptic geodatabase.
I don't know what is going on here. I better just delete these tables and clean up this mess.
Wait, I can't delete the tmpTable using the same syntax that worked in ArcGIS 9.2? I guess if the tables aren't really being created in-memory, then it makes sense the Delete_management function won't find them there. The autocomplete in the Python window wants to delete "tmpTable," without the reference to "in_memory." I will give that a try:
Well, at least that worked, but I don't know which tmpTable the autocomplete was talking about. Fortunately, running the command again did clean up the other tmpTable.
Creating feature classes in-memory behaves the same way. Also, the corresponding tools in Toolbox for creating tables and feature classes demonstrate the same behavior. There is definitely enough consistency here to not just be a bug in a specific tool/function. Who knows, maybe in_memory means on-disk in ArcGIS 10.0.
The first part in this series had an example that actually moved some data into an in-memory workspace. It can't hurt to repeat that here before coming to any conclusions. First, load those U.S. State boundaries again.
Well, there we are again, a copy of features loaded into an in-memory workspace. What? GPInMemoryWorkspace? I can't say whether I expected this result or not. So, does in_memory mean in-memory or on-disk? Obviously something changed between ArcGIS 9.2 and ArcGIS 10.0, but what?
The short answer, Background Processing.
Not only was Background Processing introduced in ArcGIS 10.0, it was turned on by default. I can't recall the reason today, but at some point years ago I had a need to disable Background Processing. At that point, I realized disabling, or not enabling, Background Processing almost reverts in_memory back to how it behaved in ArcGIS 9.2 and 9.3/9.3.1.
Interestingly enough, all of the examples above turn out very similar in ArcGIS 10.2.2. I would argue the situation in ArcGIS 10.2.2 is slightly worse than back in ArcGIS 10.0. For example, running the CreateTable_management function twice and then attempting to delete tmpTable using a fully specified in_memory path gives us:
In ArcGIS 10.0, the Delete_management function failed because tmpTable didn't actually exist in-memory, which seems logical. In ArcGIS 10.2.2, the Delete_management function succeeds, but at deleting nothing! Granted, it did return a warning that tmpTable doesn't exist in-memory, but then it continues on in deleting nothing and returning a successful result. I can't speak for others, but if I call a function to delete an object and that object doesn't exist, I usually expect an error to be returned.
Better yet, see what happens in ArcGIS 10.2.2 when you disable Background Processing, create a table in-memory, and try to use a fully specified in_memory path to delete it:
You can ostensibly successfully delete the table three times and yet it still exists! And, this is after it has warned you it doesn't exist when it clearly does, and in-memory.
It is obvious that things changed at ArcGIS 10.0 with the in-memory workspace, particularly with the use of 'in_memory.' I don't know what all changed, but there is a connection with Background processing. Furthermore, the changes have persisted throughout the ArcGIS 10.x product series. I think it is time for me to RT(?)M and see what the documentation has to say about all of these changes.