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.NET Forum / .NET Framework / ADO.NET / April 2006problem with no rows being returned - but rows are there
Hi, It seems that this issue is occurring at several client sites, though never in house. At some point, some (all?) queries run by our software start returning no rows. But the rows are there in the database - and restarting IIS (this is a web product) seems to resolve the issue. Even the following query: SELECT SERVERPROPERTY('productversion') Returns no rows under these conditions. Like I said, restarting IIS, makes things go back to normal, and all the queries being run by the .NET code are returning the expected results. There is no apparent way to reproduce the problem or force it to happen. There are no exceptions from the ADO.NET code - other then obviously our own code, relying on certain pieces of data that isn't being retrieved for some reason. No apparent problems opening connections or closing them, or running the queries. Just Anyone seen anything like this? Some sort of odd networking issue? Any ideas? Have you run a SQL Profiler trace to verify that your queries are making it to SQL Server? -Alan > Hi, > [quoted text clipped - 20 lines] > Anyone seen anything like this? Some sort of odd networking issue? Any > ideas? This is at client sites, so as you can imagine, it is difficult to get these things done. I have asked for it, and still waiting for it. It's hard to imagine that ADO.NET would just return an empty result set instead of throwing an exception complaing of a connection problem or whatever. Especially since as far as the code execution is concerned, the connection gets opened succesfully. I am suspecting some sort of network problem, maybe related to connection pooling (since an IIS reset fixes things for a while). The hard part is, it's impossible to tell what the problem is, or how to resolve it so that the code can at least tell there is a network problem and handle things appropriately. > Have you run a SQL Profiler trace to verify that your queries are > making it to SQL Server? [quoted text clipped - 31 lines] >> Anyone seen anything like this? Some sort of odd networking issue? Any >> ideas? I guess this is kindof hard to phrase, but are you receiving an empty result set (e.g., columns, but no rows) or are you uncertain that any results are being returned? Is it possible that there could be a thread synchronization issue causing concurrency issues in multiple threads accessing stateful objects? -Alan Not certain of anything. I know for sure no rows are returned. The error message is 'invalid attempt to read when no data is present', which is the message when trying to read out of a datareader that is not pointing to a row. And of course we expect a query like "SELECT SERVERPROPERTY('productversion')" to always come back with something. All the code that is running is written synchronously. No threads being created, nothing fancy. This is only happening at 1 or 2 particular client site. Everyone else is fine, running identical software and doing more or less similar things. Also, user load doesn't seem to be a factor, as we were told this happens during times when there is no heavy load or anything on the server. >I guess this is kindof hard to phrase, but are you receiving an empty > result set (e.g., columns, but no rows) or are you uncertain that any [quoted text clipped - 3 lines] > > -Alan Are you sure the error is coming from that part of the code? Put another way, maybe the connection is bad, but error handling prevents an error from being generated when you connect, or execute your SQL against a closed connection. If something goes wrong with your connections or your queries, and the error is suppressed, then you will still get to the code where you try to process the result set. I know you said the connections are fine, but this is what it counts like to me. > Not certain of anything. I know for sure no rows are returned. The error > message is 'invalid attempt to read when no data is present', which is the [quoted text clipped - 18 lines] > > > > -Alan I am positive that the connection is being opened. There is no error code around connection opening. Besides, at that point, there would be a nullreferenceexception on trying to access the datareader object - which is not the case. If there was an exception earlier on, then we would see whatever that is - general network error, etc. The connection is definitely being opened without any exceptions. > Are you sure the error is coming from that part of the code? Put another > way, maybe the connection is bad, but error handling prevents an error [quoted text clipped - 36 lines] >> > >> > -Alan Sounds like you're using a SqlDataReader. Is there any logic that takes place the first time you call Read() on your SqlDataReader that may cause it to fire more than once? I've occasionally seen, under certain conditions, events firing multiple times, or being wired up multiple times in ASP.NET. I'm totally blind to your implementation, but if you're keeping anything open during the execution cycle of whatever you're feeding to your AJAX stuff is it possible that an event could be firing multiple times, thus trying to read something that's already been read? -Alan > Not certain of anything. I know for sure no rows are returned. The error > message is 'invalid attempt to read when no data is present', which is the [quoted text clipped - 18 lines] > > > > -Alan No, there is no such logic. Like I said, this problem is easily remedied by an IIS reset. So identical code - will run perfectly fine once the IIS reset has been done. If it were calling Read twice, then resetting IIS would be meaningless. > Sounds like you're using a SqlDataReader. Is there any logic that takes > place the first time you call Read() on your SqlDataReader that may [quoted text clipped - 32 lines] >> > >> > -Alan Also, please keep in mind, that these are only 1 or 2 clients out of hundreds having this problem. We can't reproduce this elsewhere, or in house, or at all on demand. It happens seemingly randomly, and only to these clients. Everyone else is fine, and everything is functioning perfectly given identical actions in the software. > Sounds like you're using a SqlDataReader. Is there any logic that takes > place the first time you call Read() on your SqlDataReader that may [quoted text clipped - 32 lines] >> > >> > -Alan Okay... take a deep breath. Now, if something works on one system and not on another what does that mean? To me it means that something is different between the systems that work and those that don't. Of course I'm just guessing, but do both systems (the ones that work and the ones that don't) have the same build of everything? Are you sure? I would not be fiddling around with the application to try to "fix" this problem as you'll likely break everyone. I would focus on which version of the framework is installed, what version of Windows, SQL Server (or Lord help you JET) is installed. This could be a bad NIC card, a disk that's full, a bad network cable or other hardware issue as well. I would catalog the two systems and compare their configs to systems that work. I would take one of the working systems and swap it with one that's failing. It might be the operator/user. Perhaps they're pushing the wrong button in the wrong sequence. Perhaps these users have MSN 8.0 beta installed and ... you get the idea.... As in a murder mystery the clues are often staring you in the face. You just have to see them... ;)  Signature____________________________________ William (Bill) Vaughn Author, Mentor, Consultant Microsoft MVP INETA Speaker www.betav.com/blog/billva www.betav.com Please reply only to the newsgroup so that others can benefit. This posting is provided "AS IS" with no warranties, and confers no rights. __________________________________ > Also, please keep in mind, that these are only 1 or 2 clients out of > hundreds having this problem. [quoted text clipped - 44 lines] >>> > >>> > -Alan Marina, Two in addition to Bill, first security settings and than IIS settings Cor > Okay... take a deep breath. Now, if something works on one system and not > on another what does that mean? To me it means that something is different [quoted text clipped - 63 lines] >>>> > >>>> > -Alan Right, that's what we are focusing on. The hardest part is looking at all the hardware potential problems - and which particular one is the problem. Especially since this is at a client site, so it's not like we are able to examine every piece of hardware involved. The client is looking at us because the software isn't working - and we can't tell them it is something in their setup, and to go figure it out. But the problem of course is their own hardware - but we have to prove it. The most baffling part, is that there isn't an exception being thrown. That would make life so much easier. It feels like the framework really should be able to tell that there is a problem and not just behave as if everything is fine and dandy, and throw an exception whenever this problem (whatever it is) appears. > Okay... take a deep breath. Now, if something works on one system and not > on another what does that mean? To me it means that something is different [quoted text clipped - 63 lines] >>>> > >>>> > -Alan Marina, Why I started to tell about Sessions, was that that came as first in my mind what can be affected during the process and is a part of IIS. Probably there is more, that is were I would start. The reseting of the IIS is your trigger for that, but as well that there should have been a process (what I assume). Just my thought, Cor > Right, that's what we are focusing on. The hardest part is looking at all > the hardware potential problems - and which particular one is the problem. [quoted text clipped - 80 lines] >>>>> > >>>>> > -Alan Ah, Cor might be on to something there. Are you using SSPI security? If so, does the specific (problem) clients have the same rights as other clients? Are they group/role-based? Signature____________________________________ William (Bill) Vaughn Author, Mentor, Consultant Microsoft MVP INETA Speaker www.betav.com/blog/billva www.betav.com Please reply only to the newsgroup so that others can benefit. This posting is provided "AS IS" with no warranties, and confers no rights. __________________________________ > Marina, > [quoted text clipped - 97 lines] >>>>>> > >>>>>> > -Alan Marina, Just a first thought, are you sure that the session time out by those clients is not somewhere on infinity (or like that). That a page who is started comes unwanted in a kind of post back situation? Just a guess, because that you said restarting the IIS wil help. Cor > Hi, > [quoted text clipped - 20 lines] > Anyone seen anything like this? Some sort of odd networking issue? Any > ideas? We are not using ASP.NET session. We also don't use the ASP.NET model of server side controls, or server forms, etc. It's basically a home grown version of AJAX (before AJAX existed). So this all happens in server side methods. The code is working just fine with regards to having all the information to connect to the database, etc. No exceptions of any kind. It's just that it seems every query the application tries to run, results in no rows. My suspicion is that an IIS reset helps because it clears out the connection pool, and that somewhere in there is the problem. However, that is just a guess, and it doesn't provide a resolution with regards to graceful recovery when this happens. > Marina, > [quoted text clipped - 30 lines] >> Anyone seen anything like this? Some sort of odd networking issue? Any >> ideas? Marina, The session is a part of IIS not only from ASPNET. It is widely used in ASP, it keeps a user connected. Cor > We are not using ASP.NET session. We also don't use the ASP.NET model of > server side controls, or server forms, etc. It's basically a home grown [quoted text clipped - 47 lines] >>> Anyone seen anything like this? Some sort of odd networking issue? Any >>> ideas? Sorry Cor, I don't really follow how that is related to the problem I was describing... > Marina, > [quoted text clipped - 55 lines] >>>> Anyone seen anything like this? Some sort of odd networking issue? Any >>>> ideas? Is it possible that IIS is caching the pages, but the SQL is working fine? So old pages are being served up? What does the memory look like on these web servers when this happens? > Sorry Cor, I don't really follow how that is related to the problem I was > describing... [quoted text clipped - 58 lines] > >>>> Anyone seen anything like this? Some sort of odd networking issue? Any > >>>> ideas? Nope, not possible. If the pages were being cached, then we wouldn't be getting errors, since no actual code would be running. It would just server up the last version. From what I understand, there are no memory or CPU problems at the time this occurrs. The only signal that there is an issue, is this behavior. > Is it possible that IIS is caching the pages, but the SQL is working fine? > So old pages are being served up? [quoted text clipped - 75 lines] > Any >> >>>> ideas? Marina, Is it possible that somehow the "bad" connection ran a "SET FMTONLY ON" transact SQL statement ? Can you run : SET FMTONLY OFF SELECT SERVERPROPERTY('productversion') to see if that returns a result set ? Stephen. > Hi, > [quoted text clipped - 20 lines] > Anyone seen anything like this? Some sort of odd networking issue? Any > ideas? This query (among others that have the same problem) are part of our software. And due to the stacktrace, I can tell that this is the query where this is happening. it's not that someone is sitting there trying to run queries and getting nowhere. It's that suddenly queries that are part of the product stop returning rows. > Marina, > [quoted text clipped - 32 lines] >> Anyone seen anything like this? Some sort of odd networking issue? Any >> ideas? Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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