I just had a generic question related to IBM Maximo Anywhere apps, as per my understanding, data gets locally stored on a device at the time you log in to the app. I was curious to know that if something changes on the Maximo side, or if there is a refresh of data on device, will the entire set of data be replaced with a fresh pull from Maximo or is it just going to be the parts that were modified and the rest remains the same? If its just a delta refresh, how does Anywhere decide what has changed?
For "transactional" data like workorders, we download the whole list but have code that merges in the records from the server with your local copies and preserves any local changes you might have pending that haven't been sent to the server yet.
For lookup data (like assets and locations), on refresh, we remove all the local lookup data and replace it from the server.
Related
I am working on an ASP.NET webforms application with Entity Framework. Also for some reports it uses a dll and in that we have explicit query to get the records from SQL Server (such as ADO).
The problem is that when I change a column such as ParentID in SQL Server, I must to reset the website in IIS to see it and this solves the problem. This dependency is not logical and I want to know why this happens? Is there any relation to caching because of calling method in the dll?
How can I solve this problem?
When you run a query against SQL server (or any database, really), the result that you see is not the data "in the database", so to speak. The query returns a copy of that data that belongs only to you. The copy of the data gets sent over the network, to the client - in your case, an ASP.NET web application - and the application does whatever it needs to do, such as show it to a user.
Once the query which retrieved the data is complete, there is no longer any link between the data in the client, and the data in the database. There is no continuous, "live" connection between the two, even if your actual database connection is still open. The database connection is merely a way to send queries to the server, and for it to send copies of the data back.
It's like taking a copy of a file from a different machine. If you copy a file from my machine, and then I update my copy, your copy doesn't instantly get updated.
If you want data in some user interface to stay perfectly up to date with the data that actually exists in the database, you have a difficult problem to solve. There is no "easy" way to do this. Or perhaps more accurately, there is no simple or efficient way to do this.
This might seem odd to you. You're thinking "well, why not? Why doesn't it just show me the values as they actually exist?". The reason is that these systems need to be able to support many users - often thousands at once - who are all both reading the database and writing to it. Imagine someone was in the middle of updating data in the database, but then they rollback their transaction. Should you see the data as it was being modified, but not committed? What if two users are trying to update "the same" data at once? All sorts of concurrency questions come into play, which basically boils down to questions about locking.
What you are encountering here is a basic principle of multi-threaded environments, which translates to systems with multiple clients: Data can't be accessed directly by multiple people at the same time. Instead, you give each person their own immutable copy.
In a web application things are even more disconnected. When the browser requests the web page, the server side of the web application gets a copy of the data from the database, and then transmits that to the browser. Once the page is loaded there is no longer any link between the web server and the database server, or any link between the web server and the web browser at the client, and certainly no link between the web browser and the database.
Ultimately, this is one of the "hard problems" in computer science. You want to know how to tell the client to invalidate their "cache", and refresh their local data. There are a few mechanisms provided by .NET to do this with SQL Server, but they are quite technical. One of them is query notifications
I have a Xamarin Forms application I would like to develop. It will have a SQLite database and I wish to make this available on iOS and Android. The database will be populated with data from a SQL Server database on the cloud with initial seed data. I'm thinking this will be about 500 rows of data with each row about 1Kb.
What I don't understand is when and how to populate this. Should I try to put the data into a CSV file and have this populate the database when the application is installed, or when it first starts? What's the normal way to populate seed data other than lines inside of the code with a huge number of insert statements.
Any help or advice on how this is normally done (I'm thinking most people do it the same way) would be much appreciated.
Thanks
Lets break the problem down.
Is the initial data that you wish to use in your app going to change over time?
If you include any pre-populated data (a SQLite, Realm, or CSV-based file, ...) and the data that you are including goes stale and you have to update it on a routine basis, you will need to publish an application update (.apk/.ipa) so your new user installs receive the updated data (more on this below).
Note: This assumes that your current users get the updated data via actually running your app and it is handling the local data updates on routine basis (background service, push notifications, data polling, etc..)
Is this a Line of Business (LoB) application published via Ad-Hoc, private Store, and/or iOS Enterprise publishing?
If you control the user base, than having to force an update install so your users get your new/updated pre-populated data might be an acceptable approach, but not a great user experience if they forced to update the application all the time... but it works...
Is this application going to be distributed via the public Apple and Google App Stores?
This is where you need to be very careful on what pre-populated data you include within your application.
If the data goes stale and you need to push an updated app version to the Stores for your new install installs, beware that it could be days (or weeks or even month+) to get that new app into the store.
The Play Store usually is less then 24 hours on publishing app updates, and while the Apple Store can be the same, do not bet on it.
We routinely see 48-72 hour delays and randomly get rejected and thus it can take a week or more to get an update app into the Apple Store. We have had rejections delaying an app update for over a month and have gone into the appeal process and even removed already existing features to get re-published
Note: Every app update to the Apple store resets your user reviews... :-(
Bottom line: You want to want to publish to the Stores when you are bug fixing and/or adding features, not to update some "static" data that is stored within your app bundle...
What does this data cost your end-user and you?
Negative costs to you as an app developer are bad reviews and uninstalls. Look at how this "data" effects the end-users access to your application and how they react. Longer download time, usually acceptable. Longer initial app startup times, less acceptable... etc....
What markets will your app be used in? Network speeds and the cost of data transfer in many markets across the world are slow and costly...
What really is the true size of the data?
I "pre-populate" a Realm data instance with thousand of rows with 5MB of JSON data in under a second. SQLite takes longer, but it is still not bad. The data itself is stored in a zip and accessed as a static file (https-based get) and at a 80% compression factor, the 1MB of compressed data is pulled from a server (AWS S3) in under one second using LTE cellular data speeds and uncompressing it as stream while deserializing the JSON on-fly to update the Realm instance adds another second...
So, the user impact is very small and I "hide" this initial pre-populate update via a first-time welcome screen and some text that the user hopefully reads before getting to the first "real" app screen...
Note: This does assume that the user will have network data access the first time they open the app... In many markets around the world, this is not true, so factor this into your app design.
I also architect the app so its data can be update on background threads during its launch (the initial one or not) and thus the user does not stand there watching a spinning busy indictor, they can at least interact with the data that they do have.
So should you include any pre-populated data in your app bundle?
Sure, when that data is absolutely required to get the user up and running as fast as possible to enhance the user experience. Games are a great example of this in bundling 100s of megabytes or even gigabytes via .obb... with the various levels, media files, etc... into the app so the user does not experience a 10+ min. wait time upon opening the app the first time.
Now this does mean that their initial download time for the install was longer as that data was bundled within the app, the overall user experience was better as users accept the download/install times and view that as a carrier/phone/service plan issue vs. the time to open your app the first time to actually get to a functional screen.
So what do?
Personally I look at this issue on a case by case basis. I look at the data and if it is not going to change and only get added to and possibly pruned over time, include it as a pre-populated SQLite or Realm store or... Why cause the user to wait for the web requests, database updates and the additional network data usage and associated costs. If the data is going to go stale, do not bundle it in your app.
As for the mechanics of installing pre-populated data:
See my answer on this SO Question about "Bundle prebuilt Realm files"
You don't have to create your sqlite database every time the app is updated.
Actually SQLiteOpenHelper provides the following two methods:
OnCreate() : you should implement this method and create your sqlite database with populated data from the server. It is called when you the app is started for the first time.
OnUpgrade(): you should implement this method if you want to modify the database (add a new table or column in a table) or populate additional data.
The database is preserved between app updates and you don't need to create it each time.
Check the following examples which explain how to use sqlite database with Xamarin:
Using Sqlite in a Xamarin.Android Application Developed using Visual Studio
and
An Introduction to Xamarin.Forms and SQLite
I have developed an application that needs to keep data sync'd locally (within the browser) and the server.
The server data is mySQL and the local data is in form of any available persistent storage (localStorage, SQLite, IndexDB etc.). But all these locally stored data have limitation of space (sometimes 5MB and sometime a bit more).
I am looking for something that may not have any limitation - or a custom design system that can create multiple instances of local storage for 1 application. Is this possible ?
The other way, I thought it could work (but I have not knowledge of a system / library that can do this) is something that will sync only the most recent amount of data with the local storage - and keep the older data on the server and only when called it can update itself. Is there a library in PHP/JS that can do this (something like facebook - the most recent data shows up fast, but as we scroll to older data it will download chuncks of data locally ?
I hope this is clear ... Thanks for your suggestions in advance.
I have a asp.net 4.0 web application that uses linqtosql to insert/update/delete data from a sql server 2005 database.
The application is elastic and therefore fits on any device... phone, ipad or desktop.
On phones and ipads users will normally have a data plan.
What I want to know is when a user is connected to my application, but not inserting/updating/deleting data, is it affecting data usage?
Also is there data usage if a user is just looking at pages or does data usage only occur when data is being inserted/updated/deleted?
Thanks
I can't tell if you're trolling or not...
But if you aren't, then you don't understand how web applications work. If it appears in the browser window then it means the user agent (the browser in the device) downloaded it from the web server, that download eats into the device's data allowance. The fact that data was possibly moved around on the server side is irrelevant.
When a web user agent (i.e. a browser) submit data back to the server (usually via a POST request) then that too will eat into the data allowance, but HTML forms typically consume less than a kilobyte of data when being sent from the client (unless you're uploading binary files or large textareas). Data allowances are usually bi-directional, so you might have 1GB to use for both upstream and downstream - the few kilobytes you use uploading a form's data are massively outweighed by the fact that most webpages thesedays weigh a few hundred kilobytes, if not more.
Of course, the right answer in this case is "profile!" - run your application yourself and see how much data you go through when performing common tasks, record your findings, and act accordingly.
In an Adobe flex applicaiton using BlazeDS AMF remoting, what is the best stategy for keeping the local data fresh and in synch with the backend database?
In a typical web application, web pages refresh the view each time they are loaded, so the data in the view is never too old.
In a Flex application, there is the tempation to load more data up-front to be shared across tabs, panels, etc. This data is typically refreshed from the backend less often, so there is a greater chance of it being stale - leading to problems when saving, etc.
So, what's the best way to overcome this problem?
a. build the Flex application as if it was a web app - reload the backend data on every possible view change
b. ignore the problem and just deal with stale data issues when they occur (at the risk of annoying users who are more likely to be working with stale data)
c. something else
In my case, keeping the data channel open via LiveCycle RTMP is not an option.
a. Consider optimizing back-end changes through a proxy that does its own notification or poling: it knows if any of the data is dirty, and will quick-return (a la a 304) if not.
b. Often, users look more than they touch. Consider one level of refresh for looking and another when they start and continue to edit.
Look at BuzzWord: it locks on edit, but also automatically saves and unlocks frequently.
Cheers
If you can't use the messaging protocol in BlazeDS, then I would have to agree that you should do RTMP polling over HTTP. The data is compressed when using RTMP in AMF which helps speed things up so the client is waiting long between updates. This would also allow you to later scale up to the push methods if the product's customer decides to pay up for the extra hardware and licenses.
You don't need Livecycle and RTMP in order to have a notification mechanism, you can do it with the channels from BlazeDS and use a streaming/long polling strategy
In the past I have gone with choice "a". If you were using Remote Objects you could setup some cache-style logic to keep them in sync on the remote end.
Sam
Can't you use RTMP over HTTP (HTTP Polling)?
That way you can still use RTMP, and although it is much slower than real RTMP you can still braodcast updates this way.
We have an app that uses RTMP to signal inserts, updates and deletes by simply broadcasting RTMP messages containing the Table/PrimaryKey pair, leaving the app to automatically update it's data. We do this over Http using RTMP.
I found this article about synchronization:
http://www.databasejournal.com/features/sybase/article.php/3769756/The-Missing-Sync.htm
It doesn't go into technical details but you can guess what kind of coding will implement this strategies.
I also don't have fancy notifications from my server so I need synchronization strategies.
For instance I have a list of companies in my modelLocator. It doesn't change really often, it's not big enough to consider pagination, I don't want to reload it all (removeAll()) on each user action but yet I don't want my application to crash or UPDATE corrupt data in case it has been UPDATED or DELETED from another instance of the application.
What I do now is saving in a SESSION the SELECT datetime. When I come back for refreshing the data I SELECT WHERE last_modified>$SESSION['lastLoad']
This way I get only rows modified after I loaded the data (most of the time 0 rows).
Obviously you need to UPDATE last_modified on each INSERT and UPDATE.
For DELETE it's more tricky. As the guy point out in his article:
"How can we send up a record that no longer exists"
You need to tell flex which item it should delete (say by ID) so you cannot really DELETE on DELETE :)
When a user delete a company you do an UPDATE instead: deleted=1
Then on refresh companies, for row where deleted=1 you just send back the ID to flex so that it makes sure this company isn't in the model anymore.
Last but not the least, you need to write a function that clean rows where deleted=1 and last_modified is older than ... 3days or whatever you think suits your needs.
The good thing is that if a user delete a row by mistake it's still in the database and you can save it from real delete within 3days.
Rather than caching on flex client, why not do caching on server side? Some reasons,
1) When you cache data on server side, its centralized and you can make sure all clients have the same state of data
2) There are much better options available on server side for caching rather than on flex. Also you can have a cron job which refreshes data based on some frequency say every 24 hours.
3) As data is cached on server and it doesn't need to fetch it from db every time, communication with flex will be much faster
Regards,
Tejas