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Re: MSSQL strange problem and ugly workaround patch... [message #20220 is a reply to message #19310]

Fri, 27 February 2009 13:26

mirek
Messages: 14291
Registered: November 2005

Ultimate Member

I have interesting followup to this bug - I believe I now know WHY and it is indeed unbelievable:

While working on ODBC, I have noticed strange problem - MSSQL server is in effect able to sustain only single SQL command with result-set (at least in default mode, there is something new called "MARS" to avoid this problem...)

This is debilitating condition make SQL apps development next to impossible (think exactly about the loop here - this is what MSSQL cannot do easily). That is why OLDDB introduces concept of "hidden connections".

To put it straight, when it detects there is some result set pending, it opens another connection to database. That means a new session that knows nothing about previous identity insert.

Now if result set is small, it is (in our testcase) fetched in one go and no more connections need to be created. However, if it is large, OLEDB creates another connection with new session.

What implication this unbelievable thing has to transaction safety or prepared statments I do not dare to predict... Sad

In any case, I am now going to fix my ODBC U++ connector so that it will work with single ODBC statement only and fetch if required. I guess it is the only safe option...

Mirek

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[Message index]

		MSSQL strange problem and ugly workaround patch... By: mirek on Mon, 24 November 2008 18:47
		Re: MSSQL strange problem and ugly workaround patch... By: unodgs on Mon, 24 November 2008 19:08
		Re: MSSQL strange problem and ugly workaround patch... By: mirek on Tue, 25 November 2008 11:25
		Re: MSSQL strange problem and ugly workaround patch... By: unodgs on Tue, 25 November 2008 16:04
		Re: MSSQL strange problem and ugly workaround patch... By: mirek on Fri, 27 February 2009 13:26

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