A client is using our app over a LAN.
A VB6 front end accesses a Jet database via DAO.
The database connection is is kept open for the duration.
They are getting errors like as though the network is down when it isn't.
If I can explain:
Sometimes when there's a dodgy network connection a query will fail giving an error along the lines of "unable to find table A". As soon as the network is up again this instance will resume working properly again.
In this case however what happens is that an instance will go down in the manner described above but if a new instance is started it will behave properly (until after a random period it too hangs) meanwhile the previous instance will keep returning error messages suggestive of a network being down and never resume working properly.
Does anyone have an idea what this could be?
*UPDATE 08 Feb2011 The problem has been resolved *
The cause of this problem was the the computer storing the database had a static IP while the rest had dynamic IPs. The static IP address fell within the range from which the dynaic ones were selected.
Eventually a dynamic address was generated identical with the static one and caused the issues described above.
Thanks to everyone for their comments
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I want to access my cloud database from my computer but the connection tab cannot load to finish so that I can enter my IPv6 address. This is the second time am experiencing this issue and my network is strong enough. It's now been 20 minutes, but still the three dots are just indicating progress that never ends.
The first time it happened I had to leave my computer and go for a walk. This really frustrates me since it's in production and rapid updates should not be delayed.
How can I fix this?
POSSIBLE CAUSE:
It happens after I re-open Mysql-workbench and it fails reason being my IPv6 has been changed possibly by my Internet Service Provider (ISP) (I dont know of other possible reasons). After Mysql-workbench fails, I go to the console to update the new one but this problem occurs.
I think Cloud SQL security (don't know exact name) is treating this a malicious access attempt hence initiating this weird delay for immediate subsequent access. If so, then this is purely impractical for b/s since my computer does not tell me that my IPv6 has changed, besides, that normal regular IPv6 updates can't be treated as malicious lest developers continue to suffer this issue.
EDIT: This time it finished loading after approximately 50 minutes.
Have you considered using the Cloud SQL proxy to connect to your instance instead of white-listing an IP? White-listing an IP can be insecure since it provides anyone on your network access, and inconvenient (as you have discovered) because if your IP changes you lose access.
The proxy uses a service account to provide authenticated access to your instance, so it will work regardless of your IP (as long as your service account has the correct permissions). Check out these instructions for a guide on starting it up.
(As a side note, it's a difficult problem to tell why your connectivity tab is failing to get load. It might be a browser add on or even a networking failure in your local network that is interfering. You can check the browser dev console to see if any errors appear)
We have a asp.net website, hosted by IIS7. The website functions normally without any problem.
But after a while, like 1 or 2 months, the Sybase database which the website connects to will produce this error whenever accessed by any application : Maximum number of connections already opened
At first we didn't realize that it was the web site's application pool that causes this, so we restart the database and everything is back to normal.
But then the 2nd time, the 3rd time ... and we came to aware that we just need to restart the application pool for those unreleased connection to be released.
I checked the source code, there was only one place has database-connect-code and it was a very simple code which connects to the db, get the results then close it :
con.open()
x = con.getdata()
con.close
Btw, after checking the application's log, there wasn't any error or exceptions so I'm pretty sure that the con.close is probably reached and executed.
So if we could rule out the possibility that there were unclosed connections in the source code, is there any other explanation for this ?
The Access database just needs to be open and it will usually crash within the next 20-40mins, resulting in the following error message:
Your network access was interrupted. To continue, close the database, and then open it again.
More details:
The database is split, with the back end and front end on a server. The computers are then connected to the server via LAN (ethernet).
Although there are multiple computers connected to the server, the database only has one user at a time.
The database has been fine for almost a year, until this week where this error has started occurring.
We never have connectivity issues with the server.
I have seen several answers saying it is:
the databases fault, as it is starting to corrupt
the servers fault, as it broken, dropping my connection briefly
microsofts fault, they should patch it
I am hoping this is a problem with the database itself, as I am not responsible for the server.
Does anyone have a definitive solution?
I have recently experienced the same problem, and it all started when I moved my DB in an extrernal disk. The same db was working just fine in the local disk, or in the previous external disk. So, i am guessing is just a bug that has to do with the disk letter changing or something like this.
The problem sounds like an unstable LAN connection OR changes the LAN location (e.g. new hardware or changs to admin settings) causing increased latency.
If you have forms in the FE bound to BE tables the latency can cause the connection to be severed resulting in the error you see.
I'm not a network admin but the main culprits I've seen are:
Users connecting to the network using a VPN using an unstable connection (cell phones, crappy wifi, or just bad ISP service).
Network admins capping persistent connections to a share causing disconnects.
Unstable network hardware or bad hardware configuration.
"Switching" between wired and wireless LAN connections.
I don't think the issue is the database other than having bound forms to a BE database which is more of a fundemental design problem than anything else.
Good luck!
I use Access 2010. I had the same issue but solved it in the following ways.
On the external data ribbon, go to the Import & link group and click on Linked Table Manager.
Click on select all.
Click on Ok to refresh the links.
In cases where the path of the BackEnd database file has been changed, browse to the new location and select the new path. This will also refresh the links. This will solve the problem. It did for me.
You wrote, "The database has been fine for almost a year, until this week where this error has started occurring."
Clearly something has recently changed for this to be happening and without narrowing the field of possibilities it's anyone's guess. However, in my experience Jet DB crashes when two or more users are accessing and editing the same record(s) at the same time. So, if you've recently added new users this is a possibility.
Note: Jet is a file-server DB not a client server, which means the app was probably designed for a specific number of front-end users. Without knowing more I would start there.
I resolved my issue on this when I figured out that I had a offline directory setup and the sync was having an issue I turned off the sync and tested it and the error went away.
This is one of the most bizarre problems I've come across since I started using OData for my mobile apps. The OData server I've developed is backed by SQL Express 2008 and this combination has been installed on 50 different servers and/or PCs over the last 15 months. All 50 servers have been running stable with consistent function for large amounts of data.
A couple of days ago one of my clients contacted me indicating that my client app (running on iOS7) was having an odd error come up when POSTing data to their server. The error had an HTTP code of 400 and the error text is "The operation couldn't be completed. (Timeout error 400.)". My first question is: why is a timeout error coming back with a 400 code? Generally when I get timeouts (due to firewall, etc) they're in the 100x range. There is no indication in the event logs on the server of ANY problems occurring. My own logs (stored in the SQL database) show no error (which is odd because I'm using the generic exception catching method in my OData service to log any problems). I haven't got to the step of adding logging of all requests as yet.
The error is only being raised when posting one particular set of data. All other posts from the device are functioning perfectly. I got the client to re-install the app (deleting all data) and then to download the data set that was causing the error. The download worked fine. We began making changes to the data to replicate what the data looked like when the error occurred in incremental changes, posting the change to the server and observing the result. Most of the incremental changes work fine but certain combinations cause the error to occur. One of the increments involves a large volume of changes and that posts fine, but subsequent alteration of any of the objects (sometimes altering as little as 6 characters in a text field) cause the error to occur. And yet in some circumstances altering objects that have already been posted to the server works without a problem.
I wiped the service components from the server and undertook a fresh install. I shifted TCP ports in case 443 had another listener causing problems. I reset the server. None of these change the behaviour of the error.
My last ditch solution is to completely re-install IIS and .NET Framework but I'd obviously like to avoid this as it's not my server... The server is overseas from my current location so debugging isn't really an option. Hoping someone has an idea as to what I can do diagnostically to try and determine the source of this bizarre 'gremlin'.
Have you tried a more thorough traffic analysis using a tool like Fiddler? The "timeout" error does indeed seem odd and what stood from you post was that your server was "overseas". Could there be something with the "times" that are being used/generated, e.g. server time, local time, etc?
Just to confirm, the "same" exact set of data always fails? Can you replicate this via a remote debugger or via localhost? If so, can you turn on "verbose errors"?
We are using ASP.NET MVC with LINQ to SQL. We added some features and tested them all to perfection on our QA box. We are using Windows Server 2003 and SQL Server 2005. So when we pushed out changes to the Live web server we also used Red Gate SQL Compare to push new database changes to the LIVE database. We tested again between the few of us, no problems. Time for bed.
The morning comes and users are starting to hit the app, and BOOM. We have no idea why this would happen as we have not been doing any new types of code things that we were not doing before. However we did notice that during the SQL Compare sync the names of all the foreign keys were different between the two databases, not the IDs in the tables, FK_AssetAsset_A0EB67 to FK_AssetAsset_B67EF8 (for example, don't remember the exact number of trailing mixed characters during the SQL Compare), we are not sure why but that is another variable in this problem.
Strangely once this was all pushed out we could then replicate the errors on QA, but not before everything was pushed to LIVE.
QA and LIVE databases are on the same SQL Server, but the apps are on different instances of Windows Server 2003.
Errors generated:
Index was outside the bounds of the array.
Invalid attempt to call FieldCount when reader is closed.
Server failed to resume the transaction.
There is already an open DataReader associated with this Command which must be closed first.
A transport-level error has occurred when sending the request to the server.
A transport-level error has occurred when receiving results from the server.
Invalid attempt to call Read when reader is closed.
Invalid attempt to call MetaData when reader is closed.
Count must be positive and count must refer to a location within the string/array/collection. Parameter name: count
ExecuteReader requires an open and available Connection. The connection's current state is connecting.
Any one have any idea what the heck could have happened?
EDIT: Since we were able to replicate the errors all of a sudden on QA, it might not be a user load issue... Needless to say we all feel really screwed here.
Concurrency always brings bugs out of the woodwork. I'd recommend you check for objects that could be shared among requests (such as static members and singletons) and refactor your code so that as little as possible is shared.
As far as specifics go, for the error "There is already an open DataReader associated with this Command which must be closed first," you may want to try adding MultipleActiveResultSets=True to your connection strings.
It sounds like you're crossing the streams a bit and trying to share DataContexts across requests. My suggestion would be to wire in a dependancy injection framework that creates a new instance of the dependancy for each request.
I use Castle's IoC and wire it into the controller factory so that when it sees a dependancy on a repository it creates a new instance of that repository for each request. If you go this route let me know and I can shoot you a few more resources.