Ayende @ Rahien

Oren Eini aka Ayende Rahien CEO of Hibernating Rhinos LTD, which develops RavenDB, a NoSQL Open Source Document Database.

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time to read 2 min | 265 words

This is going to be my last LightSwitch post for a while.

I wanted to talk about something that I found which was at once both very surprising and Doh! at the same time.

Take a look here:


What you don’t know is this was generated from a request similar to this one:

wget http://localhost:22940/Services/LSTest-Implementation-ApplicationDataDomainService.svc/binary/AnimalsSet_All?$orderby=it.Id&$take=45&$includeTotalCount=

What made me choke was that the size of the response for this was 2.3 MB.

Can you guess why?

The image took up most of the data, obviously. In fact, I just dropped an image from my camera, so it was a pretty big one.

And that lead to another problem. It is obviously a really bad idea to send that image on the wire all the time, but LightSwitch make is so easy, indeed, even after I noticed the size of the request, it took me a while to understand what exactly is causing the issue.

And there doesn’t seems to be any easy way to tell LightSwitch that we want to put the property here, but only load it in certain circumstances. For that matter, I would generally want to make the image accessible via HTTP, which means that I gain advantages such as parallel downloads, caching, etc.

But there doesn’t seems to be any (obvious) way to do something as simple as binding a property to an Image control’s Url property.

time to read 2 min | 219 words

Something that I found many high level tools are really bad at is source control, so I thought that I would give LightSwitch a chance there.

I created a Git repository and shoved everything into it, then I decided that I would rename a property and see what is going on.

I changed the Animals.Species to Animals.AnimalType, which gives me:


This is precisely what I wanted to see.

Let us see what happen when I add a new table. And that created a new set in the ApplicationDefinition.lsml file.

Overall, this is much better than I feared.

I am still concerned about having everything in a single file (which is a receipt for having a lot of merge conflicts), but at least you can diff & work with it, assuming that you know how the file format works, and is seems like it is at least a semi reasonable one.

Nevertheless, as promised:

True story, I used to have a lot of ravens in my backyard, but they seem to have gone away single my dog killed one of them, about a week after RavenDB’s launch.

time to read 9 min | 1691 words

I thought it would be a good idea to see what sort of data access behavior LightSwitch applications have. So I hook it up with the EntityFramework Profiler and took it for a spin.

It is interesting to note that it seems that every operation that is running is running in the context of a distributed transaction:


There is a time & place to use DTC, but in general, you should avoid them until you really need them. I assume that this is something that is actually being triggered by WCF behavior, not intentional.

Now, let us look at what a simple search looks like:


This search results in:


That sound? Yes, the one that you just heard. That is the sound of a DBA somewhere expiring. The presentation about LightSwitch touted how you can search every field. And you certainly can. You can also swim across the English channel, but I found that taking the train seems to be an easier way to go about doing this.

Doing this sort of searching is going to be:

  • Very expensive once you have any reasonable amount of data.
  • Prevent usage of indexes to optimize performance.

In other words, this is an extremely brute force approach for this, and it is going to be pretty bad from performance perspective.

Interestingly, it seems that LS is using optimistic concurrency by default.


I wonder why they use the slowest method possible for this, instead of using version numbers.

Now, let see how it handles references. I think that I run into something which is a problem, consider:


Which generates:


This make sense only if you can think of the underlying data model. It certainly seems backward to me.

I fixed that, and created four animals, each as the parent of the other:


Which is nice, except that here is the SQL required to generate this screen:

-- statement #1
SELECT [GroupBy1].[A1] AS [C1]
        FROM   [dbo].[AnimalsSet] AS [Extent1]) AS [GroupBy1]

-- statement #2
SELECT   TOP ( 45 ) [Extent1].[Id]              AS [Id],
                    [Extent1].[Name]            AS [Name],
                    [Extent1].[DateOfBirth]     AS [DateOfBirth],
                    [Extent1].[Species]         AS [Species],
                    [Extent1].[Color]           AS [Color],
                    [Extent1].[Pic]             AS [Pic],
                    [Extent1].[Animals_Animals] AS [Animals_Animals]
FROM     (SELECT [Extent1].[Id]                      AS [Id],
                 [Extent1].[Name]                    AS [Name],
                 [Extent1].[DateOfBirth]             AS [DateOfBirth],
                 [Extent1].[Species]                 AS [Species],
                 [Extent1].[Color]                   AS [Color],
                 [Extent1].[Pic]                     AS [Pic],
                 [Extent1].[Animals_Animals]         AS [Animals_Animals],
                   OVER(ORDER BY [Extent1].[Id] ASC) AS [row_number]
          FROM   [dbo].[AnimalsSet] AS [Extent1]) AS [Extent1]
WHERE    [Extent1].[row_number] > 0
ORDER BY [Extent1].[Id] ASC

-- statement #3
SELECT [Extent1].[Id]              AS [Id],
       [Extent1].[Name]            AS [Name],
       [Extent1].[DateOfBirth]     AS [DateOfBirth],
       [Extent1].[Species]         AS [Species],
       [Extent1].[Color]           AS [Color],
       [Extent1].[Pic]             AS [Pic],
       [Extent1].[Animals_Animals] AS [Animals_Animals]
FROM   [dbo].[AnimalsSet] AS [Extent1]
WHERE  1 = [Extent1].[Id]

-- statement #4
SELECT [Extent1].[Id]              AS [Id],
       [Extent1].[Name]            AS [Name],
       [Extent1].[DateOfBirth]     AS [DateOfBirth],
       [Extent1].[Species]         AS [Species],
       [Extent1].[Color]           AS [Color],
       [Extent1].[Pic]             AS [Pic],
       [Extent1].[Animals_Animals] AS [Animals_Animals]
FROM   [dbo].[AnimalsSet] AS [Extent1]
WHERE  2 = [Extent1].[Id]

-- statement #5
SELECT [Extent1].[Id]              AS [Id],
       [Extent1].[Name]            AS [Name],
       [Extent1].[DateOfBirth]     AS [DateOfBirth],
       [Extent1].[Species]         AS [Species],
       [Extent1].[Color]           AS [Color],
       [Extent1].[Pic]             AS [Pic],
       [Extent1].[Animals_Animals] AS [Animals_Animals]
FROM   [dbo].[AnimalsSet] AS [Extent1]
WHERE  3 = [Extent1].[Id]

I told you that there is a select n+1 builtin into the product, now didn’t I?

Now, to make things just that much worse, it isn’t actually a Select N+1 that you’ll easily recognize. because this doesn’t happen on a single request. Instead, we have a multi tier Select N+1.


What is actually happening is that in this case, we make the first request to get the data, then we make an additional web request per returned result to get the data about the parent.

And I think that you’ll have to admit that a Parent->>Children association isn’t something that is out of the ordinary. In typical system, where you may have many associations, this “feature” alone is going to slow the system to a crawl.

time to read 2 min | 293 words

This post is to help everyone who want to understand what LightSwitch is going to do under the covers. It allows you to see exactly what is going on with the database interaction using Entity Framework Profiler.

In your LightSwitch application, switch to file view:


In the server project, add a reference to HibernatingRhinos.Profiler.Appender.v4.0, which you can find in the EF Prof download.


Open the ApplicationDataService file inside the UserCode directory:


Add a static constructor with a call to initialize the entity framework profiler:

public partial class ApplicationDataService
    static ApplicationDataService()

This is it!

You’re now able to work with the Entity Framework Profiler and see what sort of queries are being generated on your behalf.


time to read 4 min | 609 words

As promised, I intend to spend some time today with LightSwitch, and see how it works. Expect a series of post on the topic. In order to make this a read scenario, I decided that that a simple app recording animals and their feed schedule is appropriately simple.

I created the following table:


Note that it has a calculated field, which is computed using:


There are several things to note here:

  • ReSharper doesn’t work with LightSwitch, which is a big minus to me.
  • The decision to use partial methods had resulted in really ugly code.
  • Why is the class called Animals? I would expect to find an inflector at work here.
  • Yes, the actual calculation is crap, I know.

This error kept appearing at random:


It appears to be a known issue, but it is incredibly annoying.

This is actually really interesting:


  • You can’t really work with the app unless you are running in debug mode. That isn’t the way I usually work, so it is a bit annoying.
  • More importantly, it confirms that this is indeed KittyHawk, which was a secret project in 2008 MVP Summit that had some hilarious aspects.

There is something that is really interesting, it takes roughly 5 – 10 seconds to start a LS application. That is a huge amount of time. I am guessing, but I would say that a lot of that is because the entire UI is built dynamically from the data source.

That would be problematic, but acceptable, except that it takes seconds to load data even after the app has been running for a while. For example, take a look here:


This is running on a quad core, 8 GB machine, in 2 tiers mode. It takes about 1 – 2 seconds to load each screen. I was actually able to capture a screen half way loaded. Yes, it is beta, I know. Yes, perf probably isn’t a priority yet, but that is still worrying.

Another issue is that while Visual Studio is very slow, busy about 50% of the time. This is when the LS app is running or not. As an a side issue, it is hard to know if the problem is with LS or VS, because of all the problems that VS has normally.


As an example of that, this is me trying to open the UserCode, it took about 10 seconds to do so.

What I like about LS is that getting to a working CRUD sample is very quick. But the problems there are pretty big, even at a cursory examination. More detailed posts touching each topic are coming shortly.


  1. Dealing with complex hierarchies in RavenDB - 2 hours from now
  2. .NET Conf 2021 talk - Extreme Architecture Performance - about one day from now
  3. Desire features in software architecture - 2 days from now
  4. An optimization story:–27% runtime costs for 8 lines of code - 5 days from now
  5. Cumulative computation with RavenDB queries - 6 days from now

And 10 more posts are pending...

There are posts all the way to Dec 21, 2021


  1. Challenge (63):
    03 Nov 2021 - The code review bug that gives me nightmares–The fix
  2. Talk (6):
    23 Apr 2020 - Advanced indexing with RavenDB
  3. Production postmortem (32):
    17 Sep 2021 - The Guinness record for page faults & high CPU
  4. re (29):
    23 Jun 2021 - The performance regression odyssey
View all series


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