I've been having lots of problems getting my application to work using an sqlite database. Everything works just fine in ripple (I presume this is because it's just using chrome's sqlite implementation). However, once I run my app on a simulator (Curve 9300, OS 6) the problems begin. I've gotten to where the app can run, create a database, and insert rows, so I know that my actual queries are fine.
My application has a javascript file that has wrappers for working with the database. This javascript file is sourced in both the listener, and the page that is the core of the application. The problem is as follows:
Install the application. The listener starts running.
Send a text message from one simulator to another. The message is saved successfully (I can verify this because my banner indicator count increases, and the number is based of off a query)
Continue sending texts, and the banner indicator will increase.
Open the application, and read all of the messages. At this point, the javascript file is loaded twice, so I have two db objects pointing to the same database.
Close the application (listener is still running)
The next text message received causes a Runtime Exception, with no further details provided.
I looked at the stack trace, and it just says that the exception took place in the callback of the sms listener. This is obvious, as that's where the queries happen. Does anyone have any idea why opening a second connection to the db causes the exception? As far I understand, the db is only locked during a transaction. There are definitely no transactions running, other than the one trying to insert the new row. Although I'm new to javascript, I'm quite sure that no variables are being shared as the javascript file is loaded in two different pages. Any ideas would be greatly appreciated.
Well, I couldn't find a solution. I don't think the blackberry sqlite implementation can handle two concurrent connections. Instead, my listener now saves incoming data to a file. The file is read in when the main application opens, and all necessary data is saved to the db then. Afterwards, the file is deleted and the application performs queries without problem. I hope this helps anyone dealing with a similar issue.
Related
I am working on a set of Classic ASP (VBScript) websites under different domains with 64bit Access (2013) database connection. Server is a shared Windows Server 2012 with IIS 8.5. The sites were not coded by me.
Everything seems to work fine for a time, but after several page calls (sometimes also at the first or only call to the site) the server does not respond for more than 20 to 30 seconds. This means: I can't call ANY page hosted on this server, even all other websites under different domains stop working for that time.
I am not sure, if plain HTML pages will respond, but it seems not. After such an issue everything is running fine again for various periods (up to 1 or 2 minutes), pages show up with normal response time, then this system hang repeats. And so on…
Finding the problem is extremely difficult, because all the sites on this shared hosting server could possibly cause this behaviour, it not necessarily seems to be triggered by my specific page call or subsequent calls, though it could be.
I am not sure, where to even look for the problem. I searched this forum and noticed some interesting answers, but not exactly to our problem. I tried Sysinternal's Process Monitor on a virtual server, where only one specific site is hosted and the same issues exists, but was not able to interpret most of the messages. I looked into event viewer log at this machine and noticed entries saying:
A trappable error (C0000005) occurred in an external object. The script cannot continue running.
But even if that sounds to be a possible reason, I am not sure where to look in the script or a log file, where I could find the trigger of all that. And on the shared host I don't even have the possibility to do that. On our local 'internal webserver' under Windows 10, where local copies of all the sites reside, I can. But I'm not sure, where to start my search.
Any help would be appreciated (and please don't needle me with proposals for switching to ASP.net or SQL - this is not possible at the moment).
I work with huge classic ASP application this error normally happens in a call for a Server.CreateObject('foo'). We have this kind of error here normally at the excel object when someone try to upload a very large .xls file. I would start mapping all the Server.CreateObject.
I'm struggling to find a solution to what I thought would be a common requirement so I'm hoping someone can help me with some pointers on what to search for/areas to explore.
Background
I'm building an iOS mobile app. I'm storing data locally using realm.io. The app is preinstalled with a snapshot of the content of a Wordpress mySQL database (it uses custom types). The content of the WP database is only written via the Wordpress install, the mobile app cannot write data.
Objective
So, I want to be able to check for changes since a given date (whenever the local database was last updated) and send the changed records to the mobile app (via the wp JSON api?).
I think I can fetch "posts since a date" but I need a full list of all create, update and delete operations since a given date.
Since the app is read-only I thought this type of one-way sync would be pretty straight forward but I can't find a common solution.
Any ideas to point me in the right direction would be great. Obviously, if anyone has any experience of doing this sort if thing with realm.io then that would be amazing :-)
Realm doesn't support yet any sort of synchronization mechanism across different files. We have an issue about that though, but you're likely searching rather for a solution in the immediate future.
Update: Realm launched the Realm Mobile Platform. This offers synchronization functionalities and would greatly simplify the solution for this use case.
You could use e.g. the server-side Node.js binding to pull new data from your MySQL Wordpress installation and push them to a global Realm served by the Realm Object Server. This can be read-only synchronized from the mobile apps, which would automatically receive the deltas and provide updated data to your users.
Whatever mechanism you come up yourself though in the meantime, it would require that you have read-write access from your iOS application to the realm database, so that you can update it with new data.
Pushing changed records as you describe is likely not going to work.
Apple's Push Notification service (APNS), which is the only back communication channel that works when your app is in the background or suspended, allows you to send very small payloads. You would use that to signalize your iOS app, that something changed on the server-side and there is new data to load. You would then initiate a request to a JSON-based API, wait for the response, map the returned JSON to Realm objects and store them in your database.
You want probably read more in the "Downloading Content in the Background" section of background execution chapter in the official App Programming Guides for iOS.
While pre-seeding the database from the app bundle seems like a nice idea, because the user wouldn't need to wait initially after downloading the app, that will enlarge the app itself with data, which might become in the future completely irrelevant.
I'm having a strange problem with ASP.NET MVC4 and Entity Framework 5: The web application I'm building retrieves data from a database and sends it as Json into a viewmodel on the page, from which it then gets presented in a table on the page. The data represents the state of some datapoints that change every now and then.
Now I observed the following behaviour:
when I run the web application from my development server, everything works fine and the shown data is up to date.
when I deploy the web app to a production server (which talks to the very same DB), the page does not represent the current state of the data
I can't breakpoint the controller method that retrieves the data, as it only occurs on the production server, but when I look into the Json data I can see that it actually is old data. So it seems like EF is caching the retrieved data. This is a serious problem as we use this web application for industrial monitoring purposes and therefore need to rely on up-to-date data.
Has anyone encountered the same issue? Any help on this is greatly appreciated!
I don't know entity framework that well but I think this has something to do with change tracking. I'd try disabling it to force EF to re-query the DB, I think (and others please can correct me if I'm wrong) but unless SaveChanges has been called on an ObjectContext if you re-query the same data the database won't be queried again.
I've used MergeOption = MergeOption.NoTracking (on the ObjectSet) to turn it off in my project.
I don't know what causes it, but I have a Node app that keeps crashing. The console says Segmentation Fault, and it looks like it happens when two Mysql objects are instantiated (using db-mysql module), which becomes very common when 10+ users are using my site (I don't post the link to the app because I'm afraid the load would crash it ;) if it can be useful I'll post it).
Do you guys have any clue? My packages are up to date. Do you have a better package to use with Mysql (assuming it's where the problem lies)? Do you also encounter Segfault issues using Nodejs (I guess not, bcs stability is one of the main advantges of Node)?
I [think] I was definitely doing something wrong: cerating a new MySQL object and connecting to the DB every time I had a reaquest. Instead, I stored the MySQL object and run a single query for each... query. Working fine so far.
My app is highly data driven, and needs to be frequently updated. Currently the MySQL database is dumped to an xml file via PHP, and when the app loads it downloads this file. Then it loads all the values in to NSMutableArray's inside of a data manager class which can be accessed anywhere in the app.
Here is the issue, the XML file produced is about 400kb, and this apparently takes several minutes to download on the EDGE network, and even for some people on 3G. So basically I'm looking for options on how to correctly cache or optimize my app's download process.
My current thought is something along the lines of caching the entire XML file on to the iPhone's hard disk, and then just serving that data up as the user navigates the app, and loading the new XML file in the background. The problem with this is that the user is now always going to see the data from the previous run, also it seems wasteful to download the entire XML file every time if only one field was changed.
TLDR: My iPhone app's download of data is slow, how would one properly minimize this effect?
I've had to deal with something like this in an app I developed over the summer.
I what did to solve it was to do an initial download of all the data from the server and place that in a database on the client along with a revision number.
Then each time the user connects again it sends the revision number to the server, if the revision number is smaller than the server revision number it sends across the new data (and only the new data) from the server, if its the same then it does nothing.
It's fairly simple and it seems to work pretty well for me.
This method does have the drawback that your server has to do a little more processing than normal but it's practically nothing and is much better than wasted bandwidth.
My suggestion would be to cache the data to a SQLite database on the iPhone. When the application starts, you sync the SQLite database with your remote database...while letting the user know that you are loading incremental data in the background.
By doing that, you get the following:
Users can use the app immediately with stale data.
You're letting the user know new data is coming.
You're storing the data in a more appropriate format.
And once the most recent data is loaded...the user gets to see it.