Friday, December 15, 2006


1946 is out today!

My apologies for the off-topic, but this flight sim just looks GREAT. I've been trying to fly IL2 FB only to find that no matter what plane I fly, I'm a damned turkey. If you are on to WW2 flight sims like me (addicted since the venerable SWOTL) 1946 has got to be your next toy - just take a look at the trailers (drool).

Thursday, December 14, 2006

How fast can you delete?

There have been a lot of interesting discussions on data insertion performance in SQL CE. The bottom line is actually quite simple - to insert at full speed, you use a base table cursor and drop any indexes. If you must have indexes you will get a lower performance. But if you want to go really slow, you use a SQL insert command.

How about deleting? The same principles apply, actually. Use a base table cursor and (if possible) drop the indexes. But what if you have to selectively delete a large number of rows in a very large table? Well, you will need an index to seek the rows to delete. You pick up the next row to delete (given a unique row ID), seek it and delete it. Simple? No. This apparently simple process can become a real headache as I have just learned.

The scenario is simple: a very large database (around 50 MB) stored on a very fast (80x) CF card. I'm given a text file containing a very large set of GUID values that correspond to rows in a table (around 150K rows) to delete. The table has 6 indexes and a PK. How fast can we go on an iPAQ 2210 (my wartime machine) deleting al the rows? We cannot just do a DELETE FROM because this is a selective algorithm - it just happens to be deleting all of the rows (the same result would apply of you were deleting most of them).

Anywhere from 7 minutes to several hours... Really. Is this an issue with the CF card? No - this is repeatable on other devices with different flash cards. Is this an issue with the indexes? Partly - if you remove all indexes but the GUID you will get better performance, but this is a restriction of the problem: I cannot drop the indexes (after all, the algorithm does not know how many rows it is supposed to delete). Is this an issue with SQL CE? No - after all there is a scenario where you delete all the rows in 7 minutes (roughly the same as the DELETE FROM command takes).

As it turns out, this is an issue with the order with which you feed the GUID values to the algorithm. The 7 minutes run was achieved with an unsorted set of GUID values (randomly fed) where the several hours run (actually this is a projection because I stopped the bastard after 30 minutes and only 25K rows deleted) was ran when the GUID values were sorted. Yes, you read correctly - sorted.

So if you are in a similar scenario, please make sure you are not deleting the rows in the same order of the index you are seeking them on. It will kill your performance.

Why does this happen? B-tree algorithms, anyone?

Thursday, November 30, 2006

Renaming a SQL CE Table From a .NET CF Application

Yes, I have addressed this issue a couple of times in the past. The difference now is that I'm providing a means for .NET CF applications to rename SQL CE table names through a native code DLL. Read about it here.

Wednesday, November 29, 2006


So how do you change a column type in SQL CE? Going back to 2.0, there was no built-in support in the SQL language. The ALTER TABLE / ALTER COLUMN options were restricted to adding or dropping the default value, or changing the IDENTITY column properties.

If you compare the 2.0 BOL with the 3.0 BOL you see no difference. The same syntax is supported with the same limitations. Well, actually not.

With SQL CE 3.0 you can change a column data type using an ALTER TABLE command. The Syntax is very simple:

ALTER TABLE table ALTER COLUMN column type

I just got a confirmation from Microsoft that this is missing from the documentation so you should see it included in future versions.

Implications of this discovery are very important to me, especially for the SQL CE table editor in Data Port Console (now in Draft 11):
  1. Editing tables for SQL CE 3.0 just got easier. Instead of recreating a table every time a user requests a change in column data types, I only need to generate an appropriate SQL command and I'm done with it.
  2. Now, how do I keep backwards compatibility with SQL CE 2.0? Well, I don't. When using the SQL CE 2.0 engine the Console code will have to recreate the table (and hope the user has the missing msdadc.dll on the device - a highly unlikely scenario).

Back to the VS2005 editor...

Thursday, November 23, 2006

Biting the DB_NUMERIC bullet

I tried hard to avoid it. I really did. I always looked at the DB_NUMERIC structure with a mix of shock and horror. How do you handle such a beast? How do you put there a number and how do you handle it?

Well, you avoid biting the bullet until you definitely have to do it. Right now I'm working on a native code text-to-SDF conversion tool for a customer and one of the types I need to handle is the dreaded numeric.

It's interesting that this is a very popular type due to the fact that it represents a fixed-precision number. What's more, you get to define the precision. The downside to this type is its sheer size: 19 bytes! As a matter of fact, a numeric value is represented as a DB_NUMERIC structure. If you look it up either on MSDN or on oledb.h, you will see what I'm talking about. The damned thing is a monster.

Now my problem was to deserialize a text representation of a numeric value and store it in a DB_NUMERIC structure so I could feed it to the SQL CE OLE DB provider. If you are thinking about using the IDataConvert interface then you can forget it because Microsoft does not provide the msdadc.dll file anymore, so you have to convert the beast by yourself.

Firstly I tried a two tier approach: convert the text to a double and then convert the double to a DB_NUMERIC (there's some code out there that does this). You have to be careful with rounding to get the conversion done, but it works... slowly.

My second approach was actually based on the first one, but I removed most of the floating point calculations. It is fast but limited to numbers with a precision of 18 digits. Take a look:

bool CDbNumeric::Parse(LPCTSTR pszText)
__int64 big = 0;
int nScale = -1;
int i;

for(pCur = pszText; *pCur == ' '; ++pCur)

if(*pCur == '-')
sign = 0;
sign = 1;

for(; *pCur && nScale; ++pCur, --nScale)
big = big * 10 + (*pCur - '0');
else if(*pCur == '.')
if(nScale > 0)
return false;

nScale = scale + 1;
return false;

memset(val, 0, sizeof(val));

for(i = 0; i < 16 && big != 0; ++i)
val[i] = (BYTE)(big & 0xFF);

big >>= 8;

return true;

It's faster, believe me.

Tuesday, November 14, 2006

Just another database?

Is SQL Mobile / Everywhere / Compact Edition just another database? Read the DDJ interview with Mark Jewett and Steve Lasker for more insight on this:

SQL Server Everywhere: Just Another Database?

Thursday, November 09, 2006

Thank you Rui!

Thank you to my fellow MVP Rui Silva for all the stuff he sends me that helps me keep my mental health.

Data Port Console Draft 6

This is a bit boring now... I will not make any more posts about the Data Port Console Draft versions unless they are worthy of notice. If you want to get the latest version of the Draft, you can use this link.

Tuesday, November 07, 2006

Data Port Console Draft 5

The Draft 5 of Data Port Console is now online. There are a couple of new features such as the revamped table designer (not fully functional yet), that integrates both column editing and index / primary key editing. Fellow MVPs Jan Yeh and Alberto Silva have been helping a lot with suggestions and bug reports, so here's my Thank You.

Anybody else out there with some bright ideas?

Monday, November 06, 2006

Microsoft SQL Server 2005 Compact Edition RC1

The Microsoft SQL Server 2005 Compact Edition RC1 is now available for download here.

JScript support on Windows Mobile

This has got to be one of the coolest things around - exposing your Windows Mobile application's features via JScript!

Thursday, November 02, 2006

Draft 3 Notes

There is something I forgot to mention about Draft 3: you have to manually deploy the new RemSqlCe.dll file to the device. Please remember that this is far from being a finished product so you will see lots of missing features, and this is one of them.

The new RemSqlCe.dll (marked as 1.50.xxxx) now supports multiple databases per physical connection. I was looking forward to implement this new feature some time ago. It was not quite necessary for products like the Wizard where you actually process one device database per connection. With DesktopSqlCe I started to feel the need to implement this but as the sales took off I simply got too busy supporting my customers cleaning off some very stupid bugs, and this was delayed.

I finally decided to rewrite the console and implementing this feature was on the top of my to-do list. Designing the multi-database support code was quite easy: I extracted most of the code that was on a single monolithic server and implemented it in a separate class. This new server class is instantiated whenever a new database is created or an existing one is opened, and a pointer to it is stored in an internal array of 256 elements (I believe you will never need to open 256 databases on a device at the same time, will you?). When you open a database using the Draft 3 code you can see the server index in the database properties window. If you get a -1 after opening the database then you are using an older version of RemSqlCe.dll - please replace it. Note that the index value will not automatically refresh after opening the database. To do so, please select another node in the tree and select the database node again.

Please send all your comments and suggestions to this forum. The best ideas will get a free license. What do you think should be in this product?
  • Integrated import / export features?
  • If so, what formats should I support?
  • What database editing features are the most important for you?
  • Should I implement some sort of SQL Command batch processing?
  • Do you want to manage other Microsoft databases from this console?
  • Should I integrate the Data Port Sync features?

Let's hear it from you!

Wednesday, November 01, 2006

Data Port Console Draft 3

Draft 3 of the Data Port Console is now online. You can now:
  • Export the table data to an Excel sheet and
  • Specify database open and creation properties

As always, remember that this is not a product yet. Most of the features you will see on the menus will not work. Although my tests have shown that the data handling is now stable (the underlying native code DLLs have been revamped to support multiple connections per Pipe), please refrain to use your production SDF files with this and use copies instead.

Tuesday, October 31, 2006

SQL Server Compact Edition

Another name change? Well... read Steve Lasker's post to find out more.

Looks like I will have to change all my product's documentation...

Tuesday, October 24, 2006

Data Port Console Draft 1

The first draft version of Data Port Console is now ready to download. Before you download this, please uderstand that this is not a product yet. Your SDF files are not safe with this software: use only backed up copies so you don't lose any valuable data. Some of the features are still partially implemented or not implemented at all. Remember: this is not a finished product, not even a Beta.

So why am I posting this? I want your feedback on how the product should evolve and I am ready to give away free licenses for the best feature ideas. Use the special forum to express yourself.

Wednesday, October 18, 2006

Handling multiple databases

I'm preparing what will be the first Data Port Console Draft for public download. It will be an unfinished piece of code: you will see lots of holes in it and I will politely ask you not to use any production database with it. But it will be good enough for you to see what is coming up and the whole "Draft" idea is to get user input while I am developing this new product. The basics are working on SQL CE Console, so let's make this one a much better tool.

One of the biggest improvements you will see is that the code now handles multiple databases per connection (DesktopSqlCe users - this will also apply to you). As a matter of fact, and as you should expect, the whole product is based on DesktopSqlCe and I am using this as an excuse to add more features to the component.

The versions so far used to tie up the Pipe (physical connection) to the SqlCeDatabase in a one-to-one relationship. No more! Now you can have more than one SqlCeDatabase object per Pipe even on a RAPI connection. This enables some interesting scenarios indeed, and the first consumer for this one will be the new Console. Stay tuned for the incoming Draft 1.

Monday, October 16, 2006

SQL CE Console Updated (1.3.700)

This update solves an interesting issue with SQL Mobile / SQL Everywhere: altering the table schema. When you need to add or change columns to a table with all the data in, SQL CE Console makes a full copy of the source table to the target table while converting the necessary data (you may need to add msdadc.dll to your device, although this is not required on the desktop). So how are IDENTITY columns handled?

With SQL CE 2.0 there are no problems because the clever OLE DB provider allows you to overwite the generated value.

SQL Mobile, on the other hand, has a mean OLE DB engine - the only way you can influence the next IDENTITY value is by altering the column's seed through either a SQL command or a low-level OLE DB interface (my solution).

To avoid changing the IDENTITY seed for every copied row I use an optimization algorithm that keeps track of the next value and only alters the column if there is a difference between the value to write and the automatically generated one. This is actually a variation of the same algorithm found in Data Port Wizard.

For all you SQL CE Console users, here's the latest download.

Thursday, October 12, 2006

Accessing SQL Mobile-specific column properties

I wrote a small article on Retrieving IDENTITY properties with the ATL OLE DB Consumer Templates. It illustrates how to create a custom restriction class to retrieve the SQL Mobile-specific column schema properties: AUTOINC_MIN, AUTOINC_MAX, AUTOINC_NEXT, AUTOINC_SEED and AUTOINC_INCREMENT.

Wednesday, September 27, 2006

SQL Syntax Highlighting

I really want the new Data Port Console to go a few steps ahead of the old SQL CE Console when it comes to useability. One of the nice additions to the product is SQL syntax highlighting on the query editor. This allows you to write stuff like:

SELECT * FROM Customers

Fonts and colors are applied as you write and now I want to extend the editor to support auto-completion. Instead of purchasing a costly component, I decided to adapt the code on this article:

Syntax highlighting textbox written in C#

The code has some bugs and gotchas, but it is easy to use and adapt to VS 2005.

Saturday, September 23, 2006

Data Port Console

I am in the early stages of development of Data Port Console, the successor to SQL CE Console. After looking at the very long list of UI design errors I decided to use the DockPanel Suite from Weifen Luo. Most of the database editing code is being reused from the old product, but packaged in a much more compelling user interface with tabbed windows and docking panels.

Combine this with the new .NET Framework 2.0 features such as a better data grid, and I am actually getting very good results and very fast. Looks like .NET is actually delivering its promise: fast time-to-market with a solid framework to support your application.

P.S.: Yes, I know it hogs memory and the CPU with what some native code purists would call needless cycles. But I'm not sure I would be able to do this as fast as I am doing now with either MFC or WTL. Anyway, the core of the code - remote database access - is still native code. The more I think of it, the more I like this combination: native code for the performance bits and managed code for the UI and managing the user environment. A killer!

Wednesday, September 13, 2006

Enumerating devices and services with the Widcomm Bluetooth stack

I've just published an article on enumerating devices and services with the Widcomm Bluetooth stack. You can find it here.

Data Port Wizard crack

Today I noticed some interesting entries in my site's log coming from Google: people searching for a crack for Data Port Wizard. This is quite flattering indeed for a product in its second year. But I believe this is also the side effect of the lack of tool support for SQL Everywhere.

Let's see if I can find a crack for this product myself (hehehe).

Tuesday, September 12, 2006

Unified Bluetooth stack access for Windows Mobile

After considering the apparently big differences between the Microsoft and the Widcomm Bluetooth stacks, I found out that there is a way to make them work under a similar API. This is especially useful for Compact Framework developers although some native developers may also benefit from a simple C type API.

The Widcomm API is oriented to C++ developers and exposes itself as a set of C++ classes that are supposed to be consumed either as-is or derived in your application. Exposing this type of API to a .NET CF developer is nothing short of impossibe unless a C layer is developed to consume the Widcomm stack while exposing a set of simple functions.

While I was writing this piece of code, I found out that the Microsoft stack could also be subject to the same treatment. So my idea was to produce two DLL files with exactly the same function exports, one for the Widcomm stack and the other for the Microsoft stack. The obvious advantage of this is that now a .NET CF application can consume the existing Bluetooth stack without having to consider the differences between the Microsoft and the Widcomm stack.

I have to say that this was a very interesting learning project, thanks to Peter Foot's help. The resulting code will be published under a series of articles and, time permitting, I will try to integrate the code in Peter's own 32feet.NET project.

Thursday, August 31, 2006

MobileServer preview

If you have been reading these posts lately you know that I am working on getting a peer to peer scenario to work with my remote data access tools. This will allow two PDAs to synchronize data just by getting close to one another within the 32 feet required by Bluetooth.

Right now this is working over Wi-Fi and Bluetooth serial COM ports (no support for sockets in the Widcomm stack, alas).

The thing that has been missing from the picture is the server code. I started by providing a standalone native application to serve a TCP / IP sockets connection. Later I split the server feature and put it in a separate DLL. The latest change was to move all that code to the device server DLL (RemSqlCe.dll) and to expose an API for the sockets server. After adding the serial port server I started writing a very simple managed code class library for users to integrate in their own applications.

This class library allows the consuming application to create a server, configure, start, stop, query its status and dispose of it. The above picture shows an instance of the sample MobileServer application running two servers on an HP iPAQ 2210 serving two different desktop PCs, one via Wi-Fi and the other via a Bluetooth COM port.

Now I have to add Bluetooth server abilities to this little beast and this means supporting both the Microsoft stack and the popular Widcomm stack (that's why I'm using the 2210). The server will be able to expose its services (either COM or sockets) via enumeration in order to make ad-hoc device pairing easier.

I expect to release the device client very soon with some P2P samples ready to run.

Monday, August 21, 2006

SQL Mobile over Bluetooth

Well, not yet what you might expect but I just finished the first version of a serial communications Pipe. This allows you to connect to a Bluetooth-enabled device through a virtual COM port as I just did with my laptop (with Targus USB Bluetooth dongle and the standard Microsoft stack) and my iPAQ 2210 (a very reliable beast with the Broadcom stack).

Nothing automatic here - I just configured a serial link between the devices and wrote the serial code to glue them both. I am ashamed to say that this was not a swift experience because my years as a mobile developer led me to overlook some of the finer points of desktop development, namely overlapped IO. Yes, porting the device code to the desktop did not quite work as I expected. Nothing at all, really. After researching into the overlapped IO mechanism, it was quite easy to set up the internal threading and queueing to simulate a RAPI Pipe over a serial port.

Next steps? 1 - Port the client code to the mobile device so you can access another devices SQL CE / Mobile databases over a Bluetooth COM port. 2 - Add support for the Microsoft stack so a device will be able to identify which partners can serve SQL Mobile data and connect via sockets. 3 - Add support for the Broadcom stack. From what I have seen, there is no sockets support in the Broadcom stack. 4 - Why not infrared?

Friday, August 18, 2006

SQL Mobile Peer to Peer

My first P2P experience with SQL Mobile has just happened: using my iPAQ 2210 with a SanDisk SD Wi-Fi card was able to connect via a wireless network to my i-mate K-Jam, open a local SQL Mobile database and enumerate all tables.

This is especially cool because I am not using revolutionary new technology - I just adapted what I had been using in my products a long time ago. Let's see a little history.

When I first shipped Data Port Wizard almost two years ago, the device component DLL (RemSqlCe.dll) was only a RAPI streamed server. Soon I understood that I could adapt the same stream code and build more transports on top of it and the TCP/IP single-threaded server came about in almost no time. In its first incarnation the server resided in a separate device DLL file, but it was not a very pratical solution. The next release of DesktopSqlCe will have a new version of RemSqlCe.dll with the socket server code included as well as a CF (1.0 and 2.0) sample that shows how to use it. And this is what I used on the K-Jam for the server.

The client uses an adapted version of the desktop's dssce.dll and Primeworks.DesktopSqlCe.dll. (In a future version, these DLL files will change their names to better reflect what they do.) This is how I was able to quickly produce pwdclice.dll (dssce.dll device version) and the new Primeworks.Data.Client.dll (Primeworks.DesktopSqlCe.dll device version). I ported the code for both DLL files in about one day (cool, huh?).

Now, besides being able to open a local device connection I can also open a TCP/IP client connection to a server device. Et voilá: P2P! Shipping in September, but I'm open to send the early builds to anyone willing to test the code.

Three final thoughts:

Why should you want to have a local connection on your device? After all, that is why you make a reference to System.Data.SqlServerCe in your application, right? Well, can you connect to either SQL CE 2.0 and SQL Mobile with the same data provider using the same application code? And can you remotely connect to another device just by changing connection properties? Now you can!

And why not add socket server code to the LocSqlCe.dll, the RemSqlCe.dll desktop counterpart? This would be a very easy way to set up a client server scenario over the internet...

On the issue of pluggable data streams, why not a virtual COM port over Bluetooth as well? Can I sync my sdf with yours via Bluetooth?

Stay tuned!

Thursday, August 10, 2006

How do I know the database version of an sdf file?

Have you ever wondered how to detect the SQL engine version of an SDF file? Here is an answer.

Monday, August 07, 2006

DesktopSqlCe redistributables updated

The redistributable files of DesktopSqlCe (LocSqlCe.dll and RemSqlCe.dll) have been updated to version 1.46.1620. This code corrects a SQL command parameter length verification bug.

Monday, July 03, 2006

SQL CE Console Updated

SQL CE Console was just updated to version 1.2.605. Besides supporting SQL Everywhere on the desktop, I corrected a few minor bugs and added timer and row count reporting to both table dumps and SQL command results. Get the updated setup here.

Thursday, June 15, 2006

Supporting SQL Everywhere

I have just updated SQL CE Console so that it supports the Microsoft SQL Server 2005 Everywhere Edition CTP. The news bit can be read in this page, where you will also find the links to the downloads.

Tuesday, June 13, 2006

Adapt your application to exotic screen resolutions

Microsoft has just launched the Adapt Your App site to help all the Mobile developer community to better adapt to the new exotic device screen resolutions. Here you will find all the resources and downloads to help you adapt you app to, say, landscape Smartphone.

Friday, June 09, 2006

SQL Everywhere CTP

In the same day I returned from MEDC Europe, I'm greeted with some great news: Microsoft released the SQL Server 2005 Everywhere Edition CTP! Thanks to Alex Yakhnin for the heads up.

Thursday, June 01, 2006

Migrating Sync to SQL Server

The first phase of the Data Port Sync migration to SQL Server (2000, MSDE, 2005 and Express) is over with the port of the Jet preparation code. It is quite interesting to see how Microsoft implements the "same" features in all of these databases. With Jet, one can do everything with OLE DB whereas with SQL Server one must resort to T-SQL to get some of the schema information. As I found out when I was developing Data Port Wizard, SQL Server does not allow you to mix direct table access (inserts) with IDENTITY_INSERT: you have to use an SQL INSERT command. Also, Jet and SQL vary wildly in how they manage IDENTITY columns: Jet makes it a piece of cake, SQL is a bit harder especially when you have to know the current seed. Finally, I found out that there is no way to create the equivalent of a ROWGUIDCOL column in Access through a SQL CREATE command - you do have to go through OLE DB.

Having said all this, I am not sure that this will be the final preparation code for SQL Server. As a matter of fact, with a more advanced database engine I will ba able to use triggers to flag any changes to the tracked tables (or so I hope...).

Wednesday, May 24, 2006

Data Port Sync Released

Version 1.0.500 of Data Port Sync has been released. I will be adding more samples to the code to better illustrate what is an arguably complex piece of software. If you want to take a look at how the whole process works, I advise you to start by the JetSync sample (only available in C# but I'm porting it to VB). This sample does the whole synchronization process for one database:
  1. Prepares the Access database for synchronization by adding the tracking columns and tables
  2. Exports the database to the device in SDF format (either SQL CE 2.0 or SQL Mobile)
  3. Tracks the changes on both ends and
  4. Merges them according to a very simple rule: the Access database always wins

There is another C# sample (Prepare) that you may use to prepare and "unprepare" Access databases and I have used it together win an end-user sample that I am also shipping (this time it's a VB sample that I will port to C#) that does steps 2 to 4 and is supposed to act as a template for a custom solution.

All thoughts and suggestions are most welcome for this product.

Friday, May 19, 2006

Thursday, May 18, 2006

Synchronization stability

Data Port Sync is now undergoing a testing phase and although things are looking bright, I had overlooked one important detail: what happens when something fails?

There are four phases to the synchronization process: 1) preparation of the Access database; 2) exporting the Access database to the device in SDF format; 3) tracking changes on both ends and 4) merging the changes. When I designed the tracking code I assumed it would be okay to immediately mark the changes in the database, both in the user table and in the tracking table. As a matter of fact, this is a reasonable solution if you just want to track changed data, but it is not very safe if you need to process this information subsequently. If that process fails, you essentially lose the tracking information (at least with the way I was doing it).

To solve this issue, the data tracker now makes no change to the database. It generates a list of changed rows (for both databases) and the generation of this list is only affected by the posterior changes made to the database. The importance of this is that if the merge process fails, I can roll everything back and rerun the data tracker. All changes will be there.

Data Port Sync will become a product by the end of this month, before I go to MEDC Europe in Nice. Stay tuned.

Thursday, May 04, 2006

SQL Mobile DateTime parameters

Looks like I have found another small issue with SQL Mobile. I found out about this after a customer reported not being able to run a parameterized INSERT command with a DataTime parameter through DesktopSqlCe. The OLE DB provider reports the DateTime value as having 8 bytes when it in fact has 16. The ADO .NET provider seems to work correctly.

Thursday, April 27, 2006

Preparing for SQL Everywhere - II

After figuring out how to make SQL Mobile work on my XP PC (I have VS 2005 installed so the license works), I decided to port to the desktop the device component DLL I use in all my products. Most of the code (like 99% of it) was immediately reused, barring the occasional precompiler tweaks. The major challenge was not to change too much on the support code and this implied simulating a RAPI or TCP/IP connection and the corresponding data streams.

The solution I came to was quite simple: two asynchronous data buffers. The first is written to by the client code (dssce.dll) and read by the server (LocSqlCe.dll). The second data buffer is used in the exact reverse way.

When I finally managed to make the whole thing work I was amazed by how slow it was... The data streaming code was the culprit because it was chewing up too much CPU bandwidth in its own thread, especially while waiting. The solution? A criteriously inserted Sleep(0) on the reader thread.

The bottom line is that DesktopSqlCe users may now develop their applications against a local SQL Mobile database. Look Ma: no PDA!

Monday, April 24, 2006

Preparing for SQL Everywhere

Since Microsoft announced that SQL Mobile would run on all desktop platforms under the "SQL Everywhere" name, I have been wondering how easy it would be to set up my development PC in order to start testing the native OLE DB interfaces.

Well, it's easy enough. First, make sure you have Visual Studio 2005 installed (one of the versions that carries the SQL Mobile bits). Second, go to the C:\Program Files\Microsoft Visual Studio 8\Common7\IDE directory and copy all the sqlce*.dll files to your C:\Windows\System32 directory. Third, register the sqlceoledb30.dll file using regsvr32.exe Finally, open the ssceoledb30.h file and copy the SQL Mobile definitions to a header file of their own.

After this very simple routine, I was able to quickly write a desktop C++ application to create an SDF file on my desktop using code borrowed from eVC3/4! You just need to include your new header file after atldbcli.h and you are done... I will give all the details in an upcoming article.

Ah, and don't forget: this only works on development machines with VS 2005 and Windows XP Tablet PC edition. These license limitations should be lifted when we get the Everywhere bits by the end of this calendar year.

Thursday, April 06, 2006

SQL Server Everywhere Edition

Paul Flessner has just announced what many of us have been asking for: SQL Mobile on desktop PCs. Read all about it here.

Tuesday, April 04, 2006

Synchronizing multiple PDAs - success!

I write this post after my first successful synchronization of one Access database and two PDAs with SQL Mobile (an iPAQ 2210 and an i-mate K-Jam). The sync code now recognizes each client through a GUID value that is stored by the client PDA. IDENTITY space partitioning is working and all PDAs are generating non-conflicting negative IDENTITY values where the Access database generates positive ones. All of this can be configured by the user or consuming application.

My final hurdles are to implement conflict rules and constraint-directed updates. Right now, there is only one conflict rule: if both the PC and the PDA have updated the same row (as identified by a GUID), the PC wins. As for constraint-directed updates (this is a pompous term that means "insert, update and delete in foreign key order") I have already devised a means to calculate an "INSERT order", the order by which it should be safe to insert new rows without FK clashes. It so happens that it is the reverse order for DELETE.

Lots of tests ahead...

Friday, March 31, 2006

MEDC Europe 2006

I am going to MEDC Europe 2006 - are you? This is the place to be if you want to stay ahead on Windows Mobile technologies. As the banner says, register now for an early-bird rebate. See you in June!

Wednesday, March 29, 2006

Synchronizing multiple PDAs

So far, the Data Port Sync preview has already some synchronization capabilities. It will only work safely with one PDA and still has no collision handling code. When the same row is updated on both ends the PDA prevails, but this will change soon as collision-handling policies become available.

The day's work was spent on calculating INSERT order for tables (reverse of DELETE) so that database structure and constraints are not violated. Also, work is under way to support multiple PDAs synchronizing against the same database.

Hope that by the end of the week I will have more to write about.

Tuesday, March 21, 2006

DataPortSync pre-released

I finally managed to get the code to synchronize an Access database with a SQL Mobile one. There are still hundreds of little issues to solve like retrieving error information from the custom Access provider and making sure the IDENTITY values are correctly recorded. But it is working!

If you want to take a look at how the code is coming, download the latest version of DesktopSqlCe (1.3.200) and the DataPortSync pre-release 1.0.200. Be prepared for a bit of a rough ride!

Wednesday, March 15, 2006

Second step to Sync

Before synchronizing two databases, one must know what has changed in both of them. Getting to know what changed involves some exercise, especially when using two database engines that will not support any data tracking (at least with exposed APIs). Microsoft Access and SQL CE / Mobile fall in this category and require some work and data in order to track changes.

After figuring out a simple means of doing this, using additional tracking tables and columns on the tracked database, I wrote a new sample using the pre-release code of Data Port Sync and DesktopSqlCe (some minor errors were corrected meanwhile). After selecting an Access database, this sample prepares it (according to the user's selection of tables and columns) and exports it to the device. Preparation involves adding new tables to the database and new columns to the tracked tables.

After all is ready, you can start playing with both databases and the code will report what changed and in what table. Tracked rows are uniquely identified across both databases with a GUID value. I expect to upload the sample to the site very soon. Stay tuned.

Monday, March 13, 2006

First step to Sync

Today, I published the first sample for a new product - Data Port Sync. This is a .NET component that handles most of the chores required to synchronize a Microsoft Access database with either SQL CE 2.0 or SQL Mobile. It's ultimate purpose is to help developers build their own customized synchronization solutions and builds on three fundamental components:
  1. A Microsoft Access data tracker - prepares a database for tracking and tracks changes made to the database. Tracking is achieved by adding some control tables and columns to the tracked tables.
  2. SQL CE / Mobile data tracker - uses the same data tracking algorithms to track changes made to a mobile database.
  3. Data transport - building on DesktopSqlCe, I'm adding some direct access features for Access databases (so that .NET developers don't have to bother with INSERT commands).
The challenge I'm facing now is to build a number of samples that will cover all the bases, from simple database export and import, to complex merging procedures. So, I'm spending most of my time writing a C# object model to wrap my C++ code, but then I'm starting to get used to it.

Here is the first sample: an Access to SQL CE 2.0 / SQL Mobile export tool. You will need to download the latest version of DesktopSqlCe (soon to be renamed).


Thursday, March 09, 2006

Another issue with BLOBs and SQL Mobile

I just received a kbAlertz with this interesting title:

An .sdf database file in SQL Server Mobile is larger than the same .sdf database file in SQL Server CE 2.0 when you use the ntext data type or the image data type

SQL Mobile is a rewrite, not an upgrade of the SQL CE 2.0 code, so one should expect some differences in behavior. I am collecting a list of these, both high and low-level and will publish them soon.

Friday, February 24, 2006

The Bookmarks and BLOBs Bug

I can now officially discuss this bug on SQL Mobile: you should be very careful when running a SQL command that returns a scrollable cursor and has BLOB columns in it.

Read more about this issue here.

Wednesday, February 22, 2006

Thread synchronization errors

This is something that scares the hell out of me. Thread synchronization is perhaps one of the most subtle arts in our trade and I keep learning every day. The bottom line is that nothing is atomic and you should always consider the worst case scenario. Always play on the safe side - assume nothing.

My last bang on the wall was quite simple. At the very heart of all my products, both on the desktop and the device sides, lies a thread that reads all the messages and stores them in a queue. The device side is simpler - the queue is simply polled. But the desktop side is a bit more complex and requires signalling events. When a properly formed message arrives and is stored in the queue, a call to SetEvent is made to signal other threads of the availability of data.

Now, when I rewrote the code for the 2.0 versions of the products, I called SetEvent before adding the message to the queue. Access to the message queue is guarded by a critical section, as it should. It so happens that adding a message to the queue is a bit lengthy (requires memory allocation) and this meant that after firing the event any thread that would test the event before the message got to the queue would be in a strange situation: there's a signal telling me there's something on the queue but the queue is still empty...

The solution is obvious - raise the event after the message is added to the queue. Humpf...

Friday, February 03, 2006


Sue Loh shows us the major differences between CEDB and EDB in this blog entry. She also leaves an interesting challenge - to write an upgrate tool.

Tuesday, January 17, 2006

Installing SQL CE 2.0 and SQL Mobile on a Storage Card

I have just published an article that describes the techniques required to install SQL CE 2.0 and SQL Mobile on a storage card in a Windows Mobile 2003 device. You can read the article here.

Wednesday, January 11, 2006

Supporting Visual Basic 6

It's very interesting to see that old VB6 is still being used by a very large number of developers. When I started to develop my component products, I always thought that the safest bet would be to provide a very low-level C API and use it to build higher-level components in C# for the .NET world.

This experience has been quite easy because the .NET Framework has lots of classes and mechanisms to suport marshalling and binary data conversions, so the supporting API can really be made very basic indeed. Not so with VB6.

Visual Basic 6 is a very old progamming language and (I think) it lacks the skills required to qualify as a systems development language. My case is quite simple. After shipping the first version of DesktopSqlCe (which only supported C and .NET), I started to get a lot of requests to port the higher level code to Visual Basic 6. And that is the unfortunate work I am doing right now.

My major gripe is the apparent lack of functions to convert from the language types to binary streams (C++: why do you need functions for that ???). The .NET Frameworks has a bewildering number of conversion classes, but VB6 lacks almost everything. Bottom line: I am adding a lot more functions to the low-level API so that VB6 can talk to it...

And yes, I am adding VARIANT support to the code...

Wednesday, January 04, 2006

K-Jam and ToolHelp

My good friend Cristiano Severini has just published his first Windows Mobile application: CSB (standing for Call and SMS Blocker). One of the chores CSB must accomplish is to shut down tmail.exe during setup in order to install MAPI filters. The setup process finishes with a soft-reset, restoring all processes.

To shut down a process, you must get a handle to it and this is usually done through the ToolHelp API. This API creates a static snapshot of all running processes and allows the application to enumerate them and kill these processes at will. Interestingly, this technique worked quite well until Cristiano tested it in a K-Jam. Being the fortunate owner of one, I was volunteered to help (forced, actually) and found out that the CreateToolhelp32Snapshot funtion would fail every time when called with the TH32CS_SNAPPROCESS flag.

Thanks to one very clever fellow MVP (Paul Tobey) and Microsoft employee (Ilya Tumanov), I now know that this function was failing because it was generating way too much data in the snapshot. To limit the amount of data it generates, one needs to add another flag: TH32CS_SNAPNOHEAPS. Interestingly, this flag is not defined in tlhelp32.h file, where it was supposed to be. Here it is, with my thanks to Paul and Ilya:

// optimization for text shell to not snapshot heaps
#define TH32CS_SNAPNOHEAPS 0x40000000