Re: [Sqlrelay-discussion] Update two databases simultaneously / Client protocol

[David M. <dav...@fi...>]

Hagen,

SQL Relay can't currently send the same query to multiple databases, 
though that is on the TODO list.

There are several challenges associated with doing it.  All center 
around what to do if the db's get out of sync.  If the query succeeds in 
one database but fails in the other, then what do you do?  Two phase 
commit could be used with some databases, but others don't support it.  
There's also the possibility of auto-incrementing columns getting out of 
sync which can't be as easily detected as failed queries.  Also, what 
should be done if a select is sent to more than one db?  Should the 
result sets be merged?  Should both be returned in their entirety?  
Should duplicates be removed?  There are a few other, more obscure 
issues as well.

Lets say though, that you just want to non-select statements to both 
databases and don't care if they get out of sync.  I believe that SQL 
Relay could be readily modified to allow that.

As for the .NET API, the protocol was once documented but that was a 
long time ago.  I kept changing the protocol, the documentation got 
behind and I quit updating it.  It's been stable for a long time now but 
there's no current documentation.  Unfortunately, you'd have to dig 
through the client-side code to understand the protocol.

I did recently get Rudiments and the SQL Relay client API to compile 
under Windows using mingw32-gcc and got the client applications to run 
under windows without Cygwin.  The name-mangling conventions are 
all-wrong for use with native, non-mingw32 apps though.  I'm working on 
getting it to compile using the MSVC compiler but I haven't gotten far 
with that yet.  If I can figure that out soon, or figure out how to 
build a COM object using mingw32, then it should be possible to use the 
SQL Relay DLL directly from the various windows languages: VB, C#, 
MSVC++, etc.  That's all unfinished at this point though.

If you're interested, I'd be happy to work on any of these things on a 
contract basis.  Just let me know.

Take care,

David Muse
dav...@fi...

On 09/08/2011 03:35 AM, Hagen Münch wrote:
>
> Hi,
>
> I haven't used SQLrelay yet and I'm wondering whether I could use it 
> for our requirements.
>
> There are different client applications (.Net web application, a unix 
> service written in C and some Script applications, e.g. written in 
> Perl) query and update an oracle database. One of the requirements is 
> that for each client UPDATE, INSERT or DELETE statement I have two 
> update two data bases simultaneously. Is there a way to configure the 
> SQLrelay to do that?
>
> The second question is, whether there is a documentation or definition 
> of the used protocol for SQLrelay clients? Since we would have to 
> connect some .Net client applications and there is no .Net client API 
> in SQLrelay I could write the .Net API myself.
>
> Thanks
>
> --Hagen
>
>
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